The official registration of the radiographer satisfies the educational requirements in the General Administrative Order (AMvB) ex. art. 34 BIG and the quality requirements of the professional group. On the basis of which is carried out radiographer is mentioned in the Diplomaregister Paramedici and / or the Quality Register Paramedics. By registration, the radiographer continues to be traced by, for example, the Health Care Inspectorate (IGZ) and the professional associations. Other organizations also intend the Quality Register Paramedics.


To be in the Paramedics Quality Register the radiographer need to request re-registration every five years. The first period of five years is determined on the basis of the diploma date. In case of re-registration, the radiographer must meet the requirements for that period. The start date of the period station local quality criteria. The quality criteria are set every five years by the Paramedics Quality Register, paramedical professional associations. To ensure that the requirements for the patient and the client-oriented exercises and expertise-enhancing activities are safeguarded for the quality of the professional practice. The quality criteria are set up in such a way that paramedics can meet the quality requirements with the set range of expertise-enhancing activities.


In  Nigeria , these professionals are generally referred to as  Radiographers  or  Medical Radiographers  to differentiate them from Industrial Radiographers. Radiographers must complete a 5-year undergraduate BSc and a compulsory one year paid internship program in a hospital after graduation before attaining a full licensing by the  Radiographers Registration Board of Nigeria . The board also registers  Radiotherapists  who have undergone the initial 5-year Radiography program before proceeding to the Radiotherapy training.  [ citation needed ]


Radiographers in Nigeria have been striving to extend their practice to include radiographic interpretation and Ultrasound services. They are also on the verge of adopting an official professional title of "Radr" or "Rr" As of 2015 [update] .
Radiographers in Nigeria normally proceed for a Masters programme and a PhD programme in the profession.
There is a recent rise in the number of radiographers available in the country unlike the situation of shortage between 2000 – 2010. [ citation needed ]


In a typical Nigerian Teaching Hospital, radiographers do not undertake sonography examinations, this is left for the radiologists, who, in some areas, have gradually improved their relationship with the radiographers in providing services in other radiographic units. The radiologist is also in charge of specific Fluoroscopic cases where the radiographer assists only with positioning and image acquisition. [ citation needed ]


Allied Health Unions (such as 'JOHESU' and 'NUAHP') that Radiographers are members of (with Nurses, Pharmacists, Physiotherapists, Laboratory Scientists, etc.), have over the years gone on strike actions to force the Nigerian government to improve their allowances/salaries in the government owned hospitals. These strikes (when it is not a response on its own) often trigger a response from the Nigerian Medical Association who will also table some requests for the medical doctors. [ citation needed ]


Apart from monetary issues, these professional bodies are also in loggerheads over non-doctors requesting to be given top administrative roles in government owned hospitals. Many radiographers, however, do not particularly involve themselves in these movements as working in a private establishment is more lucrative. [ citation needed ]


Some Radiographers in Nigeria are also keen on setting up a "Department of Radiography" in the government owned hospitals which will not be under the Head of the Radiology Department. Some hospitals however have an understanding between the Radiology head (a Radiologist) and the Chief Radiographer where all radiographers are directly answerable to their Chief, and not the HOD. [ citation needed ]


X-Ray Technicians  (فني اشعة) in  Saudi Arabia  must successfully undertake a degree level program at a recognised higher-level education institution in Nursing before undertaking further study in radiographic imaging at university for typically 2 to 3 years; this must include a year's experience in a hospital. Upon completion, graduates are qualified X-Ray Technicians and can commence clinical practice. [ 56 ]


The  SCoR  is the professional body and union for UK radiographers. In the United Kingdom, there is ambiguity in the use of the term  Radiographer  as this does not differentiate between Therapeutic Radiographers (also known as Radiotherapists) and  Diagnostic Radiographers . As a result, all of these titles are protected titles within the United Kingdom and can not be used by any persons who has not undertaken formal study and registered with the  Health and Care Professions Council  (HCPC). In order to practise Radiography in the United Kingdom candidates must now successfully obtain a pass in a degree level programme from an accredited institution. Degrees are offered by universities across the UK and last for at least 3 years in England, Wales and Northern Ireland; and 4 years in Scotland. [ 57 ] [ 58 ]  Student Diagnostic Radiographers spend a significant amount of time working at various hospitals affiliated with their university during their studies to meet the requirement for registration with the HCPC.


They specialise in the acquisition of radiographs of General Practitioner referred (GP) patients, Outpatients, Emergency Department (ED) referred patients and Inpatients. They conduct mobile X-rays on wards and in other departments where patients are too critical to be moved and work as part of the operating team in mainly Orthopaedic and Urology cases, offering surgeons live radiographic imaging. Once qualified, Diagnostic Radiographers are able to acquire X-rays without supervision and work as part of the imaging team. They will have basic head examination qualifications in CT and even basic experience of MRI, Ultrasound and Nuclear Medicine.


Diagnostic Radiographers can specialise in-house or through a university course as a postgraduate in CT, MRI, Ultrasound or Nuclear Medicine with opportunities to gain an MSc or PhD in their field. Diagnostic Radiographers in the UK are also taking on roles that were typically only undertaken by the Radiologist (a medical doctor who specialised in interpreting X-rays), Urologist or Cardiologist in the past. [ 59 ]  This extended practice includes various interventional procedures not excluding barium enemas, barium meals/swallows, peripheral angioplasties, nerve root injections, central line insertions and many other procedures.


The professional body and workers union for Radiographers in the United Kingdom is the  Society and College of Radiographers (SCoR) . The union has been heavily involved in extending practice of Radiographers in the United Kingdom and has helped expand the role of the Radiographer greatly.


Radiographers are now able to write reports and diagnose pathologies and/or conditions seen on differing diagnostic media after completing a HCPC and SCoR accredited university course; [ 60 ] [ 61 ]  completing a course in this modality allows the Radiographer to become a reporting Radiographer in their chosen specialty. [ 62 ]


Diagnostic Radiographers are able to become supplementary prescribers which allows them the capacity to prescribe medications in partnership with an independent prescriber (a doctor or a dentist); the supplementary prescriber is to implement an agreed Clinical Management Plan for an individual patient with that patient's agreement. [ 63 ]  An accredited university course must be undertaken before this role extension is annotated onto a HCPC registrant's record. [ 64 ]  It is thought that in the future Diagnostic Radiographers in will gain independent prescribing rights, however this is currently limited by their restricted and varied scope of practice. In 2016, the introduction of independent prescribing right was agreed for Therapeutic Radiographers after a consultation by the  Medicines and Healthcare products Regulatory Agency (MHRA) [ 65 ]


In the United States, these professionals are known as  Radiologic Technologists . Formal training programs in radiography range in length that leads to a certificate, an associate or a bachelor's degree. The American Registry of Radiologic Technologists (ARRT), the primary credentialing organisation for Radiologic Technologists in the United States, requires that candidates for ARRT Certification Exams must have an associate degree at minimum as of January, 2015, effectively ending non-degree granting diploma programs. [ 66 ]  Accreditation is primarily through The Joint Review Committee on Education in Radiologic Technology (JRCERT), the only agency recognised by the United States Department of Education and the Council for Higher Education Accreditation to grant accreditation to both traditional and online programs in Radiography, Radiation Therapy, Magnetic Resonance Imaging, and Medical Dosimetry. An online page where prospective students can check the accreditation of programs is maintained by JRCERT. [ 67 ]


Radiologic Technology students study  anatomy ,  physiology ,  physics ,  radiopharmacology ,  pathology ,  biology , research,  nursing ,  medical imaging ,  diagnosis ,  radiologic instrumentation ,  emergency medical procedures ,  medical imaging techniques ,  patient care ,  medical ethics  and  general chemistry . Schooling also includes significant amounts of documented practicum supervised by Registered Technologists in various clinical settings where the classroom theory is translated to practical knowledge and real world experience. The change from Film to Digital imaging has changed training as film quality assurance and quality control is largely obsolete. The role of computer workstations to produce synthetic images for Radiologists has steadily increased the need for computer skills as has electronic medical record software.


After primary training and licensure, continuing education is required to maintain licensure and certification with the ARRT, who sets the accepted national guidelines. The ARRT requires 24 Units of accredited continuing education every two years and the laws and the regulations of most states accept this standard. Continuing formal education or the passing of an advanced practice speciality exam may also be accepted for continuing education credit. The  American Society of Radiologic Technologists  (ASRT), [ 68 ]  a professional association for people in Medical Imaging and Therapy, offers members and others continuing education materials in various media that meet the requirements of the ARRT for continuing education. [ 69 ]  Additional requirements are set forth for technologists who specialise in mammography by the US FDA. [ 70 ]


A new and evolving career for Radiologic Technologists is that of the Registered Radiologist Assistant (RRA) [ 71 ]  who is an experienced technologist (a type of Physician Assistant) who has completed additional education, training, and has passed exams to function as radiologist extenders. [ 72 ] [ 73 ]  A list of the 9 currently accredited RRA programs is maintained by the ARRT and can be accessed online. [ 74 ]  Candidates for the RRA certification must possess a bachelor's degree at minimum. [ 75 ]   [ citation needed ]


Registered Radiologist Assistant (RRA), a new advanced practice radiographer career path in the United States for experienced technologists. RRAs do not interpret studies in the manner of the reporting radiographer. [ 76 ]  The role has been accepted by the  American College of Radiology  (ACR). [ 77 ]


A  radiological information system  ( RIS ) [ 1 ]  is the core system for the electronic management of  medical imaging  departments. The major functions of the RIS can include patient scheduling,  resource management , examination performance tracking, reporting, results distribution, and procedure billing. [ 2 ]  RIS complements  HIS (hospital information systems)  and  PACS (picture archiving and communication system) , and is critical to efficient workflow to  radiology  practices. [ 3 ]


Radiological information systems commonly support the following features: [ 1 ]


In addition, a RIS often supports the following: [ 2 ]


The electronic production of a visual  image  by  ionising radiation  on a  radiation detector  and displayed on a display  monitor  or similar screen. [ 1 ] [ 2 ]


This  physics -related article is a  stub . You can help Wikipedia by  expanding it .


A  rectilinear scanner  is an  imaging  device, used to capture emission from  radiopharmaceuticals  in  nuclear medicine . The image is created by physically moving a  radiation detector  over the surface of a radioactive patient. It has become obsolete in medical imaging, largely replaced by the  gamma camera  since the late 1960s. [ 1 ] [ 2 ] [ 3 ]


One of the first rectilinear scanners was developed by Benedict Cassen in 1950. Before then hand-held detectors had been used to locate radioactive materials in patients, but the Cassen system (designed for  Iodine-131 ) combined a motor driven  photomultiplier tube  and printing mechanism. [ 2 ] [ 4 ]  Subsequent developments improved the detection systems, movement, display and printing of images. [ 5 ] [ 6 ]


Cassen's original rectilinear scanner used  calcium tungstate  (CaWo 4 ) crystal as the radiation detector. Later systems used a  Sodium iodide  (NaI)  scintillator , as in a gamma camera. [ 7 ]  The detector must be connected by mechanical or electronic means to an output system. This could be a simple light source over  photographic film ,  dot matrix printer ,  oscilloscope  or  television screen . [ 8 ] [ 9 ] [ 10 ]


The patient is administered with a radioactive pharmaceutical agent, such as radio- iodine  which will naturally collect in the  thyroid . The detector moves in a  raster pattern  over studied area of the patient, making a constant count rate. A  collimator  restricts detection to a small area directly below its position so that by the end of the scan emission from the whole study area has been detected. The output method is designed such that positional and detection information is maintained. For example, when using a light source and film the light is moved in tandem with the detector, and the intensity of light produced increases with an increase in activity, producing dark areas on the film. [ 11 ] [ 12 ]


Disadvantages include the very long imaging time (several minutes) due to the need to separately cover each target area, unlike a gamma camera which has a much larger  field of view , and the motion artefacts this can result in. [ 13 ] [ 14 ]


Reed's rules  are a set of guidelines developed by  Joseph O. Reed  in interpretation of  pediatric   radiology . [ 1 ]


Reed's rules are as follows:


Reid's base line  is used for an unambiguous definition of the orientation of the  human skull  in  conventional radiography ,  computer tomography  (CT), and  magnetic resonance imaging  (MRI) studies. [ 1 ]  It is defined as a line drawn from the inferior margin of the orbit ( Orbitale  point) to the auricular point (center of the orifice of the external acoustic meatus,  Auriculare  point) and extending backward to the center of the occipital bone. [ 2 ]  Reid's base line is used as the zero plane in computed tomography. Paediatric base line is an anatomic line that maintains a fixed relation to facial bones throughout the period of growth.


In 1962, the World Federation of  Radiology  defined it as the line between the  infraorbital margin  and the upper margin of the  external auditory meatus .


With the head upright, it is typically tilted about 7 degrees nose up with respect to the horizontal plane.


Schuller's view  is a lateral  radiographic  view of  skull  principally used for viewing  mastoid cells . [ 1 ]  The central beam of  X-rays  passes from one side of the head and is at an angle of 25°  caudad  to the radiographic plate. This angulation prevents overlap of images of the two  mastoid bones . The radiograph for each mastoid is taken separately. Schuller's view serves as an alternate view to the  Law  projection which uses a 15° angle of patient's face toward the image receptor and a 15° caudal angulation of the computed radiography (CR) to achieve the same result, a lateral mastoid air cells view without overlap of the opposite side. Under examination the outer ear ( auricle ) can be taped forward to avoid a  cartilage  shadow around mastoid. Older editions of  Merrill's Atlas of  Radiographic Positioning and Procedures  books have detailed explanation of these and other mastoid positions. [ 2 ]  Newer version of texts often omits this because of the rarity of this exam in lieu of  computed tomography  ( CT  scan scans) studies.


Simultaneous algebraic reconstruction technique  ( SART ) is a  computerized tomography  (CT)  imaging  algorithm useful in cases when the projection data is limited; it was proposed by  Anders Andersen  and  Avinash Kak  in 1984. [ 1 ]
It generates a good reconstruction in just one iteration and it is superior to standard  algebraic reconstruction technique  (ART).


As a measure of its popularity, researchers have proposed various extensions to
SART: OS-SART, FA-SART, VW-OS-SART, [ 2 ]  SARTF, etc. Researchers have also studied how SART can best be implemented on different  parallel processing  architectures. SART and its proposed extensions are used in emission CT in  nuclear medicine , dynamic CT, [ 3 ]  and holographic  tomography , and other reconstruction applications. [ 4 ]   Convergence
of the SART algorithm was theoretically established in 2004 by Jiang and Wang. [ 5 ]  Further convergence analysis was done by Yan. [ 6 ]


An application of SART to ionosphere was presented by Hobiger et al. [ 7 ]  Their  method does not use matrix algebra and therefore it can be implemented in a low-level programming language. Its convergence speed is significantly higher than that of classical SART. A discrete version of SART called DART was developed by Batenburg and Sijbers. [ 8 ]


Within the  medical  field of  otology , the  Stenvers projection  is a radiological technique that provides an oblique view of the skull and establishes a better perspective on the  petrous bone ,  bony labyrinth , and  internal auditory canal . [ 1 ]  It focuses on the posteroanterior and lateral planes.


The Stenvers projection was named after the physician Hendrik Willem Stenvers (1889–1973) of Utrecht, who developed it in 1917. [ 2 ]  It was described in 1938 by Schütz along with the lateral projection, and later recommended by Muntean and Fink in 1941. [ 3 ]


For the Stenvers projection, a patient is placed facing the film, with the head flexed slightly and rotated 45 degrees away from the side being examined. [ 1 ]  The X-ray beam will be angled 10 to 15 degrees caudal. [ 4 ]


Surgical planning  is the preoperative method of pre-visualising a surgical intervention, in order to predefine the surgical steps and furthermore the  bone segment navigation  in the context of  computer-assisted surgery . [ 1 ]
The surgical planning is most important in  neurosurgery  and  oral and maxillofacial surgery . The transfer of the surgical planning to the patient is generally made using a  medical navigation system .


The imagistic  dataset  used for surgical planning is mainly based on a  CT  or  MRI . In  oral and maxillofacial surgery , a different, more "traditional" surgical planning can be used for  orthognatic surgery , based on cast models fixed into an  articulator . [ citation needed ]


In order to make a surgical planning, one would need a  3D  image of the patient. The starting point was made by  G. Hounsfield  in the 1970s, by using  CT  in order to record data about the anatomical situation of the patients. [ 2 ]  In the 1980s, advances were made by the radiologist  M. Vannier  and his team, by creating the first computed three-dimensional reconstruction from a  CT  dataset. [ 3 ]  In the early 1990s, the surgical planning was performed by using  stereolithographic models . [ 4 ]  During the late 1990s, the first  full computer-based  virtual surgical planning was made for  osteotomies , and then transferred to the operating theatre by a  navigation system . [ 5 ]  Currently 3D Printed models are also used to plan a procedure and improve patient outcomes. [ 6 ]


The first commercially available neurosurgical planning systems appeared in the 1990s (the StealthStation by  Medtronic , [ 7 ]  the VectorVision by  Brainlab [ 8 ] ). As newer imaging modalities emerged providing increasing anatomical and functional detail for the patient in the 2000s, these surgical planning systems started to incorporate  virtual reality  technology to facilitate the visualisation and manipulation of the 3D data. One example of such systems is the  Dextroscope , manufactured by  Volume Interactions Pte Ltd . The Dextroscope is mostly used in the planning of complex neurosurgical procedures. [ 9 ] [ 10 ] [ 11 ] [ 12 ]


Teleradiology  is the transmission of radiological patient images from procedures such as  x-rays  photographs,  Computed tomography  (CT), and  MRI  imaging, from one location to another for the purposes of sharing studies with other radiologists and physicians. Teleradiology allows radiologists to provide services without actually having to be at the location of the patient.  This is particularly important when a sub-specialist such as an MRI radiologist, neuroradiologist, pediatric radiologist, or musculoskeletal radiologist is needed, since these professionals are generally only located in large metropolitan areas working during daytime hours. Teleradiology allows for specialists to be available at all times.


Teleradiology utilizes standard network technologies such as the  Internet ,  telephone  lines,  wide area networks ,  local area networks  (LAN) and the latest advanced technologies such as  medical cloud computing . Specialized software is used to transmit the images and enable the radiologist to effectively analyze potentially hundreds of images of a given study. Technologies such as advanced graphics processing, voice recognition, artificial intelligence, and image compression are often used in teleradiology. Through teleradiology and mobile  DICOM  viewers, images can be sent to another part of the hospital or to other locations around the world with equal effort. [ 1 ]


Teleradiology is a growth technology given that imaging procedures are growing approximately 15% annually against an increase of only 2% in the radiologist population. [ 2 ]


Teleradiologists can provide a preliminary read for emergency room cases and other emergency cases or a final read for the official patient record and for use in billing.


Preliminary reports include all pertinent findings and a telephone call for any critical findings. For some teleradiology services, the turnaround time is rapid with a 30-minute standard turnaround and expedited for critical and stroke studies.


Teleradiology final reports can be provided for emergency and non-emergency studies. Final reports include all findings and require access to prior studies and all relevant patient information for a complete diagnosis. Telephone calls with any critical findings are signs of quality services.


Teleradiology preliminary or final reports can be provided for all doctors and hospitals overflow studies. Teleradiology can be available for intermittent coverage as an extension of practices and will provide patients with the highest quality care.


Some teleradiologists are fellowship trained and have a wide variety of subspecialty expertise including such difficult-to-find areas as neuroradiology, pediatric neuroradiology, thoracic imaging, musculoskeletal radiology, mammography, and nuclear cardiology. [ 3 ]
There are also various medical practitioners who are not radiologists that take on studies in radiology to become sub specialists in their respected fields, an example of this is dentistry where  oral and maxillofacial radiology  allows those in dentistry to specialize in the acquisition and interpretation of radiographic imaging studies performed for diagnosis of treatment guidance for conditions affecting the maxillofacial region. [ 4 ]


In the United States,  Medicare  and  Medicaid  laws require the teleradiologist to be on U.S. soil in order to qualify for reimbursement of the Final Read.


In addition, advanced teleradiology systems must also be HIPAA compliant, which helps to ensure patients' privacy. HIPAA (Health Insurance Portability and Accountability Act of 1996) is a uniform, federal floor of privacy protections for consumers. It limits the ways that entities can use patients' personal information and protects the privacy of all medical information no matter what form it is in. Quality teleradiology must abide by important HIPAA rules to ensure patients' privacy is protected.


Also State laws governing the licensing requirements and medical malpractice insurance coverage required for physicians vary from state to state. Ensuring compliance with these laws is a significant overhead expense for larger multi-state teleradiology groups.


Medicare (Australia)  has identical requirements to that of the United States, where the guidelines are provided by the Department of Health and Ageing, and government based payments fall under the Health Insurance Act. [ 5 ]


The regulations in Australia are also conducted at both federal and state levels, ensuring that strict guidelines are adhered to at all times, with regular yearly updates and amendments are introduced (usually around March and November of every year), ensuring that the legislation is kept up to date with changes in the industry.


One of the most recent changes to Medicare and radiology / teleradiology in Australia was the introduction of the Diagnostic Imaging Accreditation Scheme (DIAS) on 1 July 2008. DIAS was introduced to further improve the quality of Diagnostic Imaging and to amend the Health Insurance Act. [ 6 ]


Until the late 1990s teleradiology was primarily used by individual radiologists to interpret occasional emergency studies from offsite locations, often in the radiologists home. The connections were made through standard analog phone lines.


Teleradiology expanded rapidly as the growth of the internet and broad band combined with new CT scanner technology to become an essential tool in trauma cases in emergency rooms throughout the country. The occasional 2–3 x-ray studies a week soon became 3–10 CT scans, or more, a night. Because ER physicians are not trained to read CT scans or MRIs, radiologists went from working 8–10 hours a day, five and half days a week to a schedule of 24 hours a day, 7 days a week coverage. This became a particularly acute challenge in smaller rural facilities that only had one solo radiologist with no other to share call.


These circumstances spawned a post-dot.com boom of firms and groups that provided  medical outsourcing , off-site teleradiology on-call services to hospitals and Radiology Groups around the country. As an example, a teleradiology firm might cover trauma at a hospital in Indiana with doctors based in Texas. Some firms even used overseas doctors in locations like Australia and India. Nighthawk, founded by Paul Berger, was the first to station U.S. licensed radiologists overseas (initially Australia and later Switzerland) to maximize the time zone difference to provide nightcall in U.S. hospitals.


Currently, teleradiology firms are facing pricing pressures. Industry consolidation is likely as there are more than 500 of these firms, large and small, throughout the United States.


Although teleradiology is flourishing in the developed world, few teleradiological links have been made to the developing world. Generally, barriers to the implementation of radiology services have also complicated setting up reliable links. [ 7 ]


Several examples of simple, low-cost nonprofit teleradiology solutions have been employed by Satellife and the Swinfen Charitable Trust. Established in 1987 by Nobel Peace Prize laureate,  Bernard Lown , Satellife (Boston) was the first non-profit organization to own and use a low Earth orbit satellite as well as mobile computing devices such as handheld computers and mobile phones for medical data communication. [ 8 ]  Starting in 1998, Swinfen Charitable Trust, a U.K. based nonprofit organization founded by Lord and Lady  Swinfen , gave healthcare personnel in remote places internet access and a digital camera, and also facilitated a low-cost telemedicine service linking doctors at hospitals in the developing world with medical and surgical consultants who gave advice at no cost. [ 9 ]


More complex solutions emerged in 2007. Operated by volunteer radiologists, Téléradiologie sans Frontières (Teleradiology without Borders), a Luxembourg-based nonprofit organization founded  by  Dr Jean-Baptiste Niedercorn and Dr Gérald Wajnapel, started to provide teleradiology imaging services to developing  countries using a professional cloud  picture archiving and communications system  (PACS). [ 10 ]


Today, many established private teleradiology practices such as Virtual Radiologic (vRad) are also involved in pilot programs with NGOs, reporting radiographs from rural health centres, free of charge. [ 11 ]


Thrombus perviousness  is an imaging biomarker which is used to estimate clot permeability from CT imaging. It reflects the ability of artery-occluding thrombi to let fluid seep into and through them. The more pervious a thrombus, the more fluid it lets through. Thrombus perviousness can be measured using radiological imaging routinely performed in the clinical management of acute ischemic stroke:  CT scans  without intravenous contrast (also called non-contrast CT, in short NCCT) combined with CT scans after intravenously administered contrast fluid ( CT-angiography , in short CTA). Pervious thrombi may let more blood pass through to the ischemic brain tissue, and/or have a larger contact surface and histopathology more sensitive for  thrombolytic medication . Thus, patients with pervious thrombi may have less brain tissue damage by stroke. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]  The value of thrombus perviousness in acute ischemic stroke treatment is currently being researched.


Emilie Santos et al. introduced the term thrombus perviousness in 2016 to estimate thrombus permeability in ischemic stroke patients. [ 1 ]  Before, Mishra et al. used ‘residual flow within the clot’, and Frölich et al. used ‘antegrade flow across incomplete vessel occlusions’ to describe an estimate of thrombus permeability. [ 2 ] [ 3 ]   Permeability  is the physical measure of the ability of a material to transmit fluids over time. To measure thrombus permeability, one needs to measure contrast flow through a clot over time and the pressure drop caused by the occlusion, which is commonly not possible in the acute management of a patient with acute ischemic stroke. Current standard diagnostic protocol for acute ischemic stroke only requires single-phase imaging, visualizing the thrombus at a snapshot in time. Therefore, thrombus perviousness was introduced as a derivative measure of  permeability.


The amount of  contrast  that seeps into a thrombus can be quantified by the density difference of thrombi between non-contrast computed tomography (NCCT) and CT angiography (CTA) images. Two measures for thrombus perviousness have been introduced: (1) the void fraction and (2) thrombus attenuation increase (TAI). [ 1 ]


The void fraction represents the ratio of the void volume within a thrombus, filled with a volume of blood (V blood ) and the volume of thrombus material (V thrombus ):

 ε

 =

 V

 blood

 V

 thrombus

 {\displaystyle {\text{ε}}={\frac {{\text{V}}_{\text{blood}}}{{\text{V}}_{\text{thrombus}}}}}

 Void fraction can be estimated by measuring the attenuation increase (Δ) between NCCT and CTA in the thrombus (Δ thrombus ) and in the contralateral artery, filling with contrast on CTA (Δ blood ), and subsequently compute the ratio of these Δs:

 ε

 =

 ρ

 CTA

 thrombus

 −

 ρ

 NCCT

 thrombus

 ρ

 CTA

 blood

 −

 ρ

 NCCT

 blood

 =

 Δ

 thrombus

 Δ

 blood

 {\displaystyle {\text{ε}}={\frac {{\text{ρ}}_{\text{CTA}}\,^{\text{thrombus}}-{\text{ρ}}_{\text{NCCT}}\,^{\text{thrombus}}}{{\text{ρ}}_{\text{CTA}}\,^{\text{blood}}-{\text{ρ}}_{\text{NCCT}}\,^{\text{blood}}}}={\frac {{\text{Δ}}_{\text{thrombus}}}{{\text{Δ}}_{\text{blood}}}}}


To measure TAI, the mean  attenuation  ( density , in  Hounsfield Units ) of a clot is measured on NCCT (ρ thrombus NCCT ) and subtracted from the thrombus density measured on CTA (ρ thrombus CTA ). [ 1 ]  CTA thrombus density increases after administration of the high-density contrast fluid used in CTA:


Δ thrombus  = ρ thrombus CTA  – ρ thrombus NCCT


A manual (volume of interest [ROI]-based) and semi-automated (full thrombus segmentation) method have been described to measure thrombus density.


In the manual thrombus perviousness assessment, spherical ROIs with a diameter of 2 mm are manually placed in the thrombus, both on NCCT and CTA. To improve reflection of possible thrombus heterogeneity, three ROIs are placed per imaging modality rather than one. [ 7 ]  The average of every three ROIs is calculated and used as ρ thrombus NCCT  and ρ thrombus CTA .


In automated measurements, the thrombus on CTA images is semi-automatically segmented in three steps. [ 8 ]


It has been shown that manual measurement tends to overestimate actual entire thrombus density, especially in low-density thrombi. [ 7 ]  Measurements based on the full thrombus show a wider variety of thrombus densities and better discrimination of high- and low-density thrombi and shows a stronger correlation with outcome measures than measurements based on 3 ROIs. [ 7 ] [ 9 ]


TAI measurements performed on CT scans with thicker slices will be less accurate, because volume averaging results in a reduction of thrombus density on NCCT. [ 10 ]  Therefore, it has been suggested to only use thin-slice CT images (≤2.5 mm) to measure thrombus perviousness. [ 8 ]


Alternative measures of similar thrombus permeability characteristics have been introduced and are still being introduced. Mishra et al. introduced the residual flow grade, which distinguishes no contrast penetration (grade 0); contrast permeating diffusely through thrombus (grade 1); and tiny hairline lumen or streak of well-defined contrast within the thrombus extending either through its entire length or part of the thrombus (grade 2).


Currently, treatment for  acute ischemic stroke  due to an occlusion of one of the arteries of the proximal anterior intracranial circulation consists of  intravenous thrombolysis  followed by  endovascular thrombectomy  for patients that arrive at the hospital within 4.5 hours of stroke onset. Patients that arrive later than 4.5 hours after onset, or have contra-indications for intravenous thrombolysis can still be eligible for endovascular thrombectomy only. Even with treatment, not all patients recover after their stroke; many are left with permanent brain damage. Increased thrombus perviousness may decrease brain damage during stroke by allowing more blood to reach the ischemic tissue. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]  Furthermore, level of perviousness may reflect histopathological composition of clots or size of contact surface for thrombolytic medication, thereby influencing effectiveness of thrombolysis. [ 1 ] [ 5 ] [ 11 ]


A number of studies has been conducted on the effects of thrombus perviousness on NCCT and CTA. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 12 ]  In addition, dynamic imaging modalities have been used to investigate thrombus perviousness/permeability in animal and laboratory studies  [ 13 ] [ 14 ] [ 15 ]  and in humans using digital subtraction angiography (DSA) and CT Perfusion/4D-CTA.  [ 3 ] [ 16 ]  4D-CTA may enable more accurate measurement of TAI, since it overcomes the influence of varying scan timing and contrast arrival in single phase CTA.  [ 16 ]


Tomographic reconstruction  is a type of multidimensional  inverse problem  where the challenge is to yield an estimate of a specific system from a finite number of  projections . The mathematical basis for tomographic imaging was laid down by  Johann Radon . A notable example of applications is the  reconstruction  of  computed tomography  (CT) where cross-sectional images of patients are obtained in non-invasive manner. Recent developments have seen the  Radon transform  and its inverse used for tasks related to realistic object insertion required for testing and evaluating computed tomography use in  airport security . [ 1 ]


This article applies in general to reconstruction methods for all kinds of  tomography , but some of the terms and physical descriptions refer directly to the reconstruction of X-ray computed tomography.


The projection of an object, resulting from the tomographic measurement process at a given angle

 θ

 {\displaystyle \theta }

 , is made up of a set of  line integrals  (see Fig. 1). A set of many such projections under different angles organized in 2D is called a sinogram (see Fig. 3). In X-ray CT, the line integral represents the total attenuation of the beam of  X-rays  as it travels in a straight line through the object. As mentioned above, the resulting image is a 2D (or 3D) model of the  attenuation coefficient . That is, we wish to find the image

 μ
 (
 x
 ,
 y
 )

 {\displaystyle \mu (x,y)}

 . The simplest and easiest way to visualise the method of scanning is the system of  parallel projection , as used in the first scanners. For this discussion we consider the data to be collected as a series of parallel rays, at position

 r

 {\displaystyle r}

 , across a projection at angle

 θ

 {\displaystyle \theta }

 . This is repeated for various angles.  Attenuation  occurs  exponentially  in tissue:


where

 μ
 (
 x
 ,
 y
 )

 {\displaystyle \mu (x,y)}

  is the attenuation coefficient as a function of position. Therefore, generally the total attenuation

 p

 {\displaystyle p}

  of a ray at position

 r

 {\displaystyle r}

 , on the projection at angle

 θ

 {\displaystyle \theta }

 , is given by the line integral:


Using the coordinate system of Figure 1, the value of

 r

 {\displaystyle r}

  onto which the point

 (
 x
 ,
 y
 )

 {\displaystyle (x,y)}

  will be projected at angle

 θ

 {\displaystyle \theta }

  is given by:


So the equation above can be rewritten as


where

 f
 (
 x
 ,
 y
 )

 {\displaystyle f(x,y)}

  represents

 μ
 (
 x
 ,
 y
 )

 {\displaystyle \mu (x,y)}

  and

 δ
 (
 )

 {\displaystyle \delta ()}

  is the  Dirac delta function . This function is known as the  Radon transform  (or  sinogram ) of the 2D object.


The  Fourier Transform  of the projection can be written as


where

 g

 θ

 (
 x
 cos

 θ
 +
 y
 sin

 θ
 )

 {\displaystyle g_{\theta }(x\cos \theta +y\sin \theta )}

  is the derivative of the  Hilbert transform  of

 p

 θ

 (
 r
 )

 {\displaystyle p_{\theta }(r)}


In theory, the inverse Radon transformation would yield the original image. The  projection-slice theorem  tells us that if we had an infinite number of one-dimensional projections of an object taken at an infinite number of angles, we could perfectly reconstruct the original object,

 f
 (
 x
 ,
 y
 )

 {\displaystyle f(x,y)}

 . However, there will only be a finite number of projections available in practice.


Assuming

 f
 (
 x
 ,
 y
 )

 {\displaystyle f(x,y)}

  has effective diameter

 d

 {\displaystyle d}

  and desired resolution is

 R

 s

 {\displaystyle R_{s}}

 , a rule of thumb for the number of projections needed for reconstruction is

 N
 >
 π
 d

 /

 R

 s

 {\displaystyle N>\pi d/R_{s}}

 [ 2 ]


Practical reconstruction algorithms have been developed to implement the process of reconstruction of a three-dimensional object from its projections. [ 3 ] [ 2 ]  These  algorithms  are designed largely based on the mathematics of the  X-ray transform , statistical knowledge of the data acquisition process and geometry of the data imaging system.


Reconstruction can be made using interpolation. Assume

 N

 {\displaystyle N}

  projections of

 f
 (
 x
 ,
 y
 )

 {\displaystyle f(x,y)}

  are generated at equally spaced angles, each sampled at the same rate. The  discrete Fourier transform  (DFT) on each projection yields sampling in the frequency domain. Combining all the frequency-sampled projections generates a polar raster in the frequency domain. The polar raster is sparse, so interpolation is used to fill the unknown DFT points, and reconstruction can be done through the  inverse discrete Fourier transform . [ 4 ]  Reconstruction performance may improve by designing methods to change the sparsity of the polar raster, facilitating the effectiveness of interpolation.


For instance, a concentric square raster in the frequency domain can be obtained by changing the angle between each projection as follow:


where

 R

 0

 {\displaystyle R_{0}}

  is highest frequency to be evaluated.


The concentric square raster improves computational efficiency by allowing all the interpolation positions to be on rectangular DFT lattice. Furthermore, it reduces the interpolation error. [ 4 ]  Yet, the Fourier-Transform algorithm has a disadvantage of producing inherently noisy output.


In practice of tomographic image reconstruction, often a stabilized and  discretized  version of the inverse Radon transform is used, known as the  filtered back projection  algorithm. [ 2 ]


With a sampled discrete system, the inverse Radon transform is


where

 Δ
 θ

 {\displaystyle \Delta \theta }

  is the angular spacing between the projections and

 k
 (
 t
 )

 {\displaystyle k(t)}

  is a Radon kernel with frequency response

 |

 ω

 |

 {\displaystyle |\omega |}

 .


The name  back-projection  comes from the fact that a one-dimensional projection needs to be filtered by a one-dimensional Radon kernel (back-projected) in order to obtain a two-dimensional signal. The filter used does not contain DC gain, so adding  DC bias  may be desirable. Reconstruction using back-projection allows better resolution than interpolation method described above. However, it induces greater noise because the filter is prone to amplify high-frequency content.


The iterative algorithm is computationally intensive but it allows the inclusion of  a priori  information about the system

 f
 (
 x
 ,
 y
 )

 {\displaystyle f(x,y)}

 . [ 2 ]


Let

 N

 {\displaystyle N}

  be the number of projections and

 D

 i

 {\displaystyle D_{i}}

  be the distortion operator for the

 i

 {\displaystyle i}

 th projection taken at an angle

 θ

 i

 {\displaystyle \theta _{i}}

 .

 {

 λ

 i

 }

 {\displaystyle \{\lambda _{i}\}}

  are a set of parameters to optimize the conversion of iterations.


An alternative family of recursive tomographic reconstruction algorithms are the  algebraic reconstruction techniques  and  iterative sparse asymptotic minimum variance .


Use of a noncollimated fan beam is common since a  collimated  beam of radiation is difficult to obtain. Fan beams will generate series of line integrals, not parallel to each other, as projections. The fan-beam system requires a 360-degree range of angles, which imposes mechanical constraints, but it allows faster signal acquisition time, which may be advantageous in certain settings such as in the field of medicine. Back projection follows a similar two-step procedure that yields reconstruction by computing weighted sum back-projections obtained from filtered projections.


Deep learning methods are widely applied to image reconstruction nowadays and have achieved impressive results in various image reconstruction tasks, including low-dose denoising, sparse-view reconstruction, limited angle tomography and metal artifact reduction. An excellent overview can be found in the special issue  [ 5 ]  of IEEE Transaction on Medical Imaging. One group of deep learning reconstruction algorithms apply post-processing neural networks to achieve image-to-image reconstruction, where input images are reconstructed by conventional reconstruction methods. Artifact reduction using the U-Net in limited angle tomography is such an example application. [ 6 ]  However, incorrect structures may occur in an image reconstructed by such a completely data-driven method, [ 7 ]  as displayed in the figure. Therefore, integration of known operators into the architecture design of neural networks appears beneficial, as described in the concept of precision learning. [ 8 ]  For example, direct image reconstruction from projection data can be learnt from the framework of filtered back-projection. [ 9 ]  Another example is to build neural networks by unrolling iterative reconstruction algorithms. [ 10 ]  Except for precision learning, using conventional reconstruction methods with deep learning reconstruction prior  [ 11 ]  is also an alternative approach to improve the image quality of deep learning reconstruction.


Tomographic systems have significant variability in their applications and geometries (locations of sources and detectors). This variability creates the need for very specific, tailored implementations of the processing and reconstruction algorithms. Thus, most CT manufacturers provide their own custom proprietary software. This is done not only to protect intellectual property, but may also be enforced by a government regulatory agency. Regardless, there are a number of general purpose tomographic reconstruction software packages that have been developed over the last couple decades, both commercial and open-source.


Most of the commercial software packages that are available for purchase focus on processing data for benchtop cone-beam CT systems. A few of these software packages include  Volume Graphics ,  InstaRecon ,  iTomography ,  Livermore Tomography Tools (LTT) , and  Cone Beam Software Tools (CST) .


Some noteworthy examples of open-source reconstruction software include: Reconstruction Toolkit (RTK),  [ 12 ]  CONRAD, [ 13 ]  TomoPy, [ 14 ]  the ASTRA toolbox, [ 15 ] [ 16 ]  PYRO-NN, [ 17 ]  ODL, [ 18 ]  TIGRE, [ 19 ]  and LEAP. [ 20 ]


Shown in the gallery is the complete process for a simple object tomography and the following tomographic reconstruction based on ART.


Transient hepatic attenuation differences  ( THAD ) are areas of  enhancement  during the arterial phase of  contrast CT  of the liver. THAD is thought to be a physiological phenomenon resulting from regional variation in the blood supply by the  portal vein  and/or the  hepatic artery . THAD may in some cases be associated with  liver tumors  such as a  hepatocellular carcinoma . [ 2 ]


A  vaginogram  is a  medical imaging  method in which a  radiocontrast agent  is injected while  X-ray pictures  are taken, to visualize structures of the  vagina . [ 1 ]  It has been used to visualize  ureterovaginal fistulas . [ 2 ] [ 3 ]


This  gynaecology  article is a  stub . You can help Wikipedia by  expanding it .


Waters' view  (also known as the  occipitomental view  or  parietoacanthial projection ) is a radiographic view of the skull. It is commonly used to get a better view of the  maxillary sinuses . An x-ray beam is angled at 45° to the  orbitomeatal line . The rays pass from behind the head and are perpendicular to the radiographic plate. Another variation of the waters places the orbitomeatal line at a 37° angle to the image receptor. It is named after the American radiologist Charles Alexander Waters.


Waters' view can be used to best visualise a number of structures in the skull.


The frontal sinus may not show the  frontal sinus  in detail. [ 1 ]


Typically, the x-ray beam is angled at 45° to the  orbitomeatal line . [ 3 ]  Another variation of the waters places the orbitomeatal line at a 37° angle to the image receptor, [ 4 ]  or 30°. [ 5 ]


Waters' view is named after the American radiologist Charles Alexander Waters. [ 6 ]  It is also known as the occipitomental view. [ 5 ]


An  X-ray tube  is a  vacuum tube  that converts electrical input power into  X-rays . [ 1 ]  The availability of this controllable source of X-rays created the field of  radiography , the imaging of partly opaque objects with penetrating  radiation . In contrast to other sources of  ionizing radiation , X-rays are only produced as long as the X-ray tube is energized. X-ray tubes are also used in  CT scanners , airport luggage scanners,  X-ray crystallography , material and structure analysis, and for industrial inspection.


Increasing demand for high-performance  computed tomography  (CT) scanning and  angiography  systems has driven development of very high-performance medical X-ray tubes.


X-ray tubes evolved from experimental  Crookes tubes  with which X-rays were first discovered on November 8, 1895, by the German physicist  Wilhelm Conrad Röntgen . The first-generation  cold cathode  or  Crookes  X-ray tubes were used until the 1920s. These tubes work by ionisation of residual gas within the tube. The positive ions bombard the cathode of the tube to release electrons, which are accelerated toward the anode and produce X-rays when they strike it. [ 2 ]  The Crookes tube was improved by  William Coolidge  in 1913. [ 3 ]  The  Coolidge  tube, also called a  hot cathode  tube, uses  thermionic emission , where a tungsten cathode is heated to a sufficiently high temperature to emit electrons, which are then accelerated toward the anode in a near perfect vacuum. [ 2 ]


Until the late 1980s, X-ray generators were merely high-voltage, AC to DC variable power supplies. In the late 1980s a different method of control was emerging, called high-speed switching. This followed the electronics technology of switching power supplies (aka  switch mode power supply ), and allowed for more accurate control of the X-ray unit, higher quality results and reduced X-ray exposures. [ citation needed ]


As with any  vacuum tube , there is a  cathode , which emits electrons into the vacuum and an  anode  to collect the electrons, thus establishing a flow of electrical current, known as the  beam , through the tube. A high  voltage  power source, for example 30 to 150  kilovolts  (kV), called the  tube voltage , is connected across cathode and anode to accelerate the electrons. The  X-ray  spectrum depends on the anode material and the accelerating voltage. [ 4 ]


Electrons from the cathode collide with the anode material, usually  tungsten ,  molybdenum  or  copper , and accelerate other electrons, ions and nuclei within the anode material. About 1% of the energy generated is emitted/radiated, usually perpendicular to the path of the electron beam, as X-rays. The rest of the energy is released as heat. Over time, tungsten will be deposited from the target onto the interior surface of the tube, including the glass surface. This will slowly darken the tube and was thought to degrade the quality of the X-ray beam. Vaporized tungsten condenses on the inside of the envelope over the "window" and thus acts as an additional filter and decreases the tube's ability to radiate heat. [ 5 ]  Eventually, the tungsten deposit may become sufficiently conductive that at high enough voltages, arcing occurs. The arc will jump from the cathode to the tungsten deposit, and then to the anode. This arcing causes an effect called " crazing " on the interior glass of the X-ray window. With time, the tube becomes unstable even at lower voltages and must be replaced. At this point, the tube assembly (also called the "tube head") is removed from the X-ray system, and replaced with a new tube assembly. The old tube assembly is shipped to a company that reloads it with a new X-ray tube. [ citation needed ]


The two X-ray photon-generating effects are generally called the ' Characteristic effect ' and the  bremsstrahlung  effect, a compound of the German  bremsen  meaning to brake, and  Strahlung  meaning  radiation . [ 6 ]


The range of  photonic energies  emitted by the system can be adjusted by changing the applied voltage, and installing aluminum filters of varying thicknesses. Aluminum filters are installed in the path of the X-ray beam to remove "soft" (non-penetrating) radiation. The number of emitted X-ray photons, or dose, are adjusted by controlling the current flow and exposure time. [ citation needed ]


Heat is produced in the focal spot of the anode. Since a small fraction (less than or equal to 1%) of electron energy is converted to X-rays, it can be ignored in heat calculations. [ 7 ]
The quantity of heat produced (in Joule) in the focal spot is given by :


Heat Unit (HU) was used in the past as an alternative to Joule. It is a convenient unit when a single-phase power source is connected to the X-ray tube. [ 7 ]  With a full-wave rectification of a  sine wave ,

 w

 {\displaystyle w}

 =

 1

 2

 ≈
 0.707

 {\displaystyle {\frac {1}{\sqrt {2}}}\approx 0.707}

 , thus the heat unit:


Crookes tubes generated the electrons needed to create X-rays by  ionization  of the residual air in the tube, instead of a heated  filament , so they were partially but not completely  evacuated . They consisted of a  glass  bulb with around 10 −6  to 5×10 −8   atmospheric pressure  of  air  (0.1 to 0.005  Pa ). They had an  aluminum   cathode  plate at one end of the tube, and a  platinum   anode  target at the other end. The anode surface was angled so that the X-rays would radiate through the side of the tube. The cathode was concave so that the electrons were focused on a small (~1 mm) spot on the anode, approximating a  point source  of X-rays, which resulted in sharper images. The tube had a third electrode, an anticathode connected to the anode. It improved the X-ray output, but the method by which it achieved this is not understood. A more common arrangement used a copper plate anticathode (similar in construction to the cathode) in line with the anode such that the anode was between the cathode and the anticathode. [ citation needed ]


To operate, a  DC  voltage of a few  kilovolts  to as much as 100 kV was applied between the anodes and the cathode, usually generated by an  induction coil , or for larger tubes, an  electrostatic machine . [ citation needed ]


Crookes tubes were unreliable. As time passed, the residual air would be absorbed by the walls of the tube, reducing the pressure. This increased the voltage across the tube, generating 'harder' X-rays, until eventually the tube stopped working. To prevent this, 'softener' devices were used (see picture). A small tube attached to the side of the main tube contained a mica sleeve or chemical that released a small amount of gas when heated, restoring the correct pressure. [ citation needed ]


The glass envelope of the tube would blacken with usage due to the X-rays affecting its structure. [ citation needed ]


In the Coolidge tube, the electrons are produced by  thermionic effect  from a  tungsten   filament  heated by an electric current. The filament is the cathode of the tube. The high voltage potential is between the cathode and the anode, the electrons are thus  accelerated , then hit the anode. [ citation needed ]


There are two designs: end-window tubes and side-window tubes. End window tubes usually have "transmission target" which is thin enough to allow X-rays to pass through the target (X-rays are emitted in the same direction as the electrons are moving.) In one common type of end-window tube, the filament is around the anode ("annular" or ring-shaped), the electrons have a curved path (half of a toroid). [ citation needed ]


What is special about side-window tubes is an  electrostatic lens  is used to focus the beam onto a very small spot on the anode. The anode is specially designed to dissipate the heat and wear resulting from this intense focused barrage of electrons. The anode is precisely angled at 1-20 degrees off perpendicular to the electron current to allow the escape of some of the X-ray photons which are emitted perpendicular to the direction of the electron current. The anode is usually made of tungsten or molybdenum. The tube has a window designed for escape of the generated X-ray photons. [ citation needed ]


The power of a Coolidge tube usually ranges from 0.1 to 18  kW . [ citation needed ]


A considerable amount of heat is generated in the focal spot (the area where the beam of electrons coming from the cathode strike to) of a stationary anode. Rather, a rotating anode lets the electron beam sweep a larger area of the anode, thus redeeming the advantage of a higher intensity of emitted radiation, along with reduced damage to the anode compared to its stationary state. [ 9 ]


The focal spot temperature can reach 2,500 °C (4,530 °F) during an exposure, and the anode assembly can reach 1,000 °C (1,830 °F) following a series of large exposures. Typical anodes are a tungsten-rhenium target on a molybdenum core, backed with graphite. The  rhenium  makes the  tungsten  more ductile and resistant to wear from the impact of the electron beams. The  molybdenum  conducts heat from the target. The  graphite  provides thermal storage for the anode, and minimizes the rotating mass of the anode.


Some X-ray examinations (such as, e.g.,  non-destructive testing  and  3-D microtomography ) need very high-resolution images and therefore require X-ray tubes that can generate very small focal spot sizes, typically below 50 μm in diameter. These tubes are called microfocus X-ray tubes. [ citation needed ]


There are two basic types of microfocus X-ray tubes: solid-anode tubes and metal-jet-anode tubes. [ citation needed ]


Solid-anode microfocus X-ray tubes  are in principle very similar to the Coolidge tube, but with the important distinction that care has been taken to be able to focus the electron beam into a very small spot on the anode. Many microfocus X-ray sources operate with focus spots in the range 5-20 μm, but in the extreme cases spots smaller than 1 μm may be produced. [ citation needed ]


The major drawback of solid-anode microfocus X-ray tubes is their very low operating power. To avoid melting the anode, the electron-beam power density must be below a maximum value. This value is somewhere in the range 0.4-0.8 W/μm depending on the anode material. [ 10 ]  This means that a solid-anode microfocus source with a 10 μm electron-beam focus can operate at a power in the range 4-8 W.


In  metal-jet-anode microfocus X-ray tubes  the solid metal anode is replaced with a jet of liquid metal, which acts as the electron-beam target. The advantage of the metal-jet anode is that the maximum electron-beam power density is significantly increased. Values in the range 3-6 W/μm have been reported for different anode materials (gallium and tin). [ 11 ] [ 12 ]  In the case with a 10 μm electron-beam focus a metal-jet-anode microfocus X-ray source may operate at 30-60 W.


The major benefit of the increased power density level for the metal-jet X-ray tube is the possibility to operate with a smaller focal spot, say 5 μm, to increase image resolution and at the same time acquire the image faster, since the power is higher (15-30 W) than for solid-anode tubes with 10 μm focal spots.


Any  vacuum tube  operating at several thousand volts or more can produce X-rays as an unwanted byproduct, raising safety issues. [ 13 ] [ 14 ]  The higher the voltage, the more penetrating the resulting radiation and the more the hazard.  CRT displays , once common in color televisions and computer displays, operate at  3-40  kilovolts  depending on size, [ 15 ]  making them the main concern among household appliances. Historically, concern has focused less on the CRT, since its thick glass envelope is impregnated with several pounds of lead for shielding, than on high voltage (HV)  rectifier  and  voltage regulator  tubes inside earlier TVs. In the late 1960s it was found that a failure in the HV supply circuit of some  General Electric  TVs could leave excessive voltages on the regulator tube, causing it to emit X-rays. The same failure mode was also observed in early revisions of Soviet-made  Rubin  TVs equipped with  GP-5   voltage-regulator tube . The models were recalled and the ensuing scandal caused the US agency responsible for regulating this hazard, the  Center for Devices and Radiological Health  of the  Food and Drug Administration  (FDA), to require that all TVs include circuits to prevent excessive voltages in the event of failure. [ 16 ]  The hazard associated with excessive voltages was eliminated with the advent of all- solid-state  TVs, which have no tubes other than the CRT. Since 1969, the FDA has limited TV X-ray emission to 0.5 mR ( milliroentgen ) per hour. As  other screen technologies  advanced, starting in the 1990s, the production of CRTs was slowly phased out. These other technologies, such as  LED ,  LCD  and  OLED , are incapable of producing x-rays due to the lack of a high voltage transformer. [ 17 ]


Interventional neuroradiology (INR)   also known as  neurointerventional surgery (NIS) ,  endovascular therapy (EVT) ,  endovascular neurosurgery , and  interventional neurology  is a medical subspecialty of   neurosurgery ,  neuroradiology ,  intervention radiology  and  neurology  specializing in minimally invasive image-based technologies and procedures used in diagnosis and treatment of diseases of the head, neck, and spine. [ 1 ]


Diagnostic angiography


Cerebral angiography  was developed by Portuguese  neurologist   Egas Moniz  at the  University of Lisbon , in order to identify central nervous system diseases such as tumors or  arteriovenous malformations . He performed the first brain angiography in  Lisbon  in 1927 [ 3 ]  by injecting an  iodinated contrast  medium into the  internal carotid artery  and using the  X-rays  discovered 30 years earlier by  Roentgen  in order to visualize the cerebral vessels. In pre-CT and pre-MRI, it was the only tool to observe the structures within the skull and was also used to diagnose extravascular pathologies.


Subsequently, European radiologists further developed the angiographic technique by replacing the traumatic direct puncture with catheterization: in 1953, Swedish physician  Sven Seldinger  introduced the technique of  arterial  and  venous catheterization  still in practice, [ 4 ]  dubbed the  Seldinger Technique.  In 1964, the Norwegian radiologist Per Amudsen was the first to perform a complete brain angiography with a transfemoral approach, as it is performed today; he then moved to San Francisco to teach the technique to American neuroradiologists. [ 5 ]  These two stages, at the basis of modern invasive vascular diagnostics, prepared the way for later therapeutic developments.


The first treatments: balloon occlusion


The first to carry out a true endovascular procedure was  Charles Dotter , the father of  angioplasty  and considered by many as the father of all  interventional radiology , as well as the first doctor to have performed endovascular treatment. On January 16, 1964, he performed a therapeutic angioplasty of a superficial  femoral artery  in an 82-year-old woman with an  ischemic  leg refusing  amputation . [ 6 ]  The artery remained open for the next two and a half years, after which the woman died of  pneumonia .


The concept of using balloons to treat  cerebrovascular   lesions  was inspired by a 1959 May Day celebration in Moscow’s Red Square. While watching children use tether lines to manipulate helium balloons, Fedor Serbinenko, a Russian neurosurgeon, began to envision small balloons moving through  tortuous arteries . [ 7 ]  In the 1970s Fedor Serbinenko developed a technique for closing  intracranial aneurysms  with balloons that were released into the internal carotid artery by  occluding  the  lumen . The first treatment was performed in 1970 in Moscow, with the occlusion of an internal carotid to treat a  carotid-cavernous fistula . He can be considered, therefore, the first interventional neuroradiologist. This technique was subsequently refined by neuroradiologists all over the world and mainly in France, where interventional neuroradiology developed and flourished.


Parallel to the development of catheters, in the radiology and neuroradiology units, image technology dramatically improved: Charles Mistretta in 1979 invented  digital subtraction angiography  (DSA), the technique currently in use. It consists of performing skull radiography under basic conditions which are then "subtracted" to the image after contrast media injection, to provide an image where only brain vessels are displayed, with great improvement in the diagnostic potential.


Coils replace balloon occlusion


Between the end of the 1980s and the beginning of the '90s, INR was suddenly revolutionized after the work of two Italian physicians:  Cesare Gianturco  and Guido Guglielmi. The first combined a deep knowledge of diagnostic radiology with a great ability to solve technical and manual problems. He invented Gianturco's coils, which he used to make the first attempts to  embolize  arteries and aneurysms. [ 8 ]  Gianturco also patented the first  endovascular stent  approved by the American FDA; [ 8 ]  a device with a great legacy. In the second half of the 1980s,  Sadek Hilal  was the first in Columbia University to use coils to treat brain aneurysms; but this technique was inaccurate and dangerous because the coils were released with little control with great risk of occluding the vessel from which the aneurysm originated (parent vessel). [ 9 ]  The coil embolization was revolutionized by the work of Guido Guglielmi in UCLA, who realized that electricity could function as a controlled release mechanism for coils; in 1991 he published two works dealing with the embolization of brain aneurysms by means of detachable platinum coils [ 10 ]  ( Guglielmi's coils ). The treatment of aneurysms was thus made more accessible and safe.


New techniques: Sole stenting and flow diversion stents


From the early 2000s, intracranial stents were used to prevent the coils inside the aneurysmal sac from protruding into the parent artery. [ 11 ] [ 12 ]  Flow diversion devices were later developed, with the function of reconstructing the vessel's normal anatomy without directly closing the aneurysm neck and therefore preserving side branches and preventing ischemia. [ 13 ]  The  sole stenting [ 14 ]  procedure involves the insertion of a stent only (without any coils) into the vessel that has an aneurysm. [ 15 ]


Not just hemorrhages: the treatment of ischemic stroke


The Souers Stroke Institute was founded in 1991 at  Saint Louis University , and its first director,  Camilo R. Gomez , M.D., is often credited with founding interventional neurology as a subspecialty in the United States. [ 16 ]


Between January and June 2015, five major randomized trials were published in the  New England Journal of Medicine  ( NEJM ) with the collaboration of interventional neuroradiologists and  stroke  neurologists (in the Netherlands, [ 17 ]  Canada, [ 18 ]  Australia, [ 19 ]  US [ 20 ]  and Spain [ 21 ] ) regarding the role of mechanical  thrombectomy  in the treatment of ischemic stroke, demonstrating that if it is performed in centers with proven experience, intra-arterial mechanical thrombectomy is more effective than traditional treatment (intravenous thrombolytic injection). The promising results of these mechanical thrombectomy trials were highlighted by the  NEJM  in an editorial, which concluded with the statement: "Endovascular equipoise no longer exists. It's about time." [ 22 ]


Thrombectomy is currently recommended by the guidelines written by the main American (AHA/ASA) [ 23 ]  and European (ESO-ESNR-ESMINT) [ 24 ]  societies of stroke neurologists and interventional neuroradiologists.


The following is a list of diseases and conditions typically treated by neurointerventionalists.


Interventional oncology  (abbreviated  IO ) is a subspecialty field of  interventional radiology  that deals with the diagnosis and treatment of  cancer  and cancer-related problems using targeted minimally invasive procedures performed under image guidance. [ 1 ] [ 2 ]  Interventional oncology has developed to a separate pillar of modern oncology and it employs  X-ray ,  ultrasound ,  computed tomography (CT)  or  magnetic resonance imaging (MRI)  to help guide miniaturized instruments (e.g. biopsy needles, ablation electrodes, intravascular catheters) to allow targeted and precise treatment of solid tumours (also known as  neoplasms ) located in various organs of the  human body , including but not limited to the  liver ,  kidneys ,  lungs , and  bones . [ 3 ] [ 4 ]  Interventional oncology treatments are routinely carried out by interventional radiologists in appropriate settings and facilities. [ 5 ]


Interventional oncology procedures are generally divided between  diagnostic  procedures that help obtain tissue diagnosis of suspicious neoplasms and therapeutic ones that aim to cure or palliate the tumour. Therapeutic interventional oncology procedures may be classified further into  ablation  techniques that destroy neoplastic tissues by delivery of some form of heat, cryo or electromagnetic energy and embolization techniques that aim to occlude the blood vessels feeding the tumour and thereby destroy it by means of  ischemia . Both ablation and embolization techniques are minimally invasive treatment, i.e. they may be delivered through the skin (in a  percutaneous  way) without the need for any skin incisions or other form of  open surgery . Hence, most treatments are nowadays offered as day case or  outpatient  appointments and patients may enjoy rapid recovery and minimal pain and discomfort with low rates of complications. [ 6 ]


Uses different types of energy to burn ( radiofrequency ablation (RFA)  and  microwave ablation (MWA) ), deliver electrical fields/electroporate ( irreversible electroporation(IRE) ) or freeze ( cryoablation ) solid tumors resulting in tumor cell death. Ablation techniques can be performed throughout the body such as in the lung, [ 7 ]  liver, [ 8 ] [ 9 ]  kidney, [ 10 ]   prostate, [ 11 ]  breast, [ 12 ]  bone, [ 13 ]  and other organs using image guidance to place a needle/probe through the skin into the target tissue.


Uses a machine that emits high frequency sound waves to kill cancer cells and provide relief for tumor-related pain, such as in the bone.


Interventional oncology has long been used to provide palliative care for patients. IO procedures can help reduce cancer-related pain and improve patients’ quality of life. Tumours can intrude into various ducts and blood vessels of the body, obstructing the vital passage of food, blood or waste. The interventional radiological treatment known as stenting can be used to re-open blockages, for example of the esophagus or bile ducts in cases of esophageal cancer or cholangiocarcinoma, respectively, considerably relieving the patient's adverse symptoms. [ 22 ]


Interventional oncology (IO) procedures are commonly applied to treat primary or  metastatic  cancer. IO treatments may be also offered in combination with any of the above oncological therapies in order to augment the therapeutic outcome in more complex or widespread (metastatic) cancer cases. There is a variety of applications of interventional oncological treatments for tumors that arise in the:


While the  surgical resection  of tumours is generally accepted to offer the best long-term solution, it is often not possible due to the size, number or location of the tumour. IR therapies may be applied to shrink the tumour, making a surgical or interventional treatment possible. Some patient groups may also be too weak to undergo open surgery. IR treatments can be applied in these complex cases to provide effective and milder forms of treatment.
Interventional oncological techniques can also be used in combination with other treatments to help increase their  efficacy . For example, IO techniques can be used to shrink large tumours making them easier to excise. Chemotherapeutic drugs can also be administered intra-arterially, increasing their potency and removing the harsh effects of system-wide application.


Patients can greatly benefit from IO treatments. The minimally invasive nature of the treatments means they cause less pain, fewer side effects and shorter recovery times. Many IO procedures can be performed on an  outpatient  basis, freeing up hospital beds and reducing costs. [ 33 ]


Cancer is a multifaceted disease group that requires a multidisciplinary approach to treatment. Numerous studies have shown that cancer patients treated in multidisciplinary environments benefit greatly from the combined expertise. Interventional Radiologists are seen as playing a major role in multidisciplinary cancer teams where they provide innovative solutions to improve combined therapies and to treat complications. [ 34 ]


Proper patient selection is the key element for the success of any medical procedure and improper conduct can have fatal consequences. Patient selection protocols must be strictly followed before treating patients with IO procedures.


IO treatments are carried out under image guidance. For this reason practitioners must have attained solid training in  radiation protection .


Interventional pulmonology  ( IP , also called  interventional pulmonary medicine ) is a maturing  medical sub-specialty  from its parent specialty of  pulmonary medicine . It deals specifically with minimally invasive  endoscopic  and percutaneous procedures for diagnosis and treatment of  neoplastic  as well as  non-neoplastic diseases  of the airways, lungs, and pleura. Many IP procedures constitute efficacious yet less invasive alternatives to  thoracic surgery .


Before the advent of  optical fibers  and advances in  anesthesiology , interventional pulmonary procedures were mostly limited to foreign body retrieval via rigid bronchoscopy.  Gustav Killian  (June 2, 1860 – February 24, 1921), a German laryngologist, performed foreign body retrievals from bronchial passages using a rigid  laryngoscope /bronchoscope whereas in the United States,  Chevalier Jackson  (1865 – 1958) was the first to use the rigid  bronchoscope . [ 1 ]  Later, Swedish internist  Hans-Christian Jacobaeus  first introduced  thoracoscopy  in a 1910 paper published in the journal  Münch med Wochenschr , before Japanese thoracic surgeon  Shiketo Ikeda  (1925 – 2001) introduced the fiberoptic bronchoscope in the late 20th century. [ 2 ] [ 3 ]  Jean-Francois Dumon from France is credited with modernizing rigid bronchoscopy in the late 20th century by introducing a novel non-metallic airway stent made of silicone, appropriately named the Dumon stent. [ 4 ]  Together, these developments laid the foundation for most of today’s interventional pulmonary techniques.


In 1978, Kopen Wang and colleagues at  Johns Hopkins Hospital  described the use of transbronchial needle aspiration (TBNA) through a rigid bronchoscope to diagnose a paratracheal  mediastinal mass . [ 5 ]  Following the advent of  endobronchial ultrasound  (EBUS), which first became available in the early 21st century, EBUS-TBNA swiftly replaced  mediastinoscopy  as the first-line in mediastinal  staging  for lung cancer. [ 6 ]  With these developments, interventional pulmonology became much more firmly established on the map of distinct subspecialties.


In 1992, the Association for Bronchology and Interventional Pulmonology (AABIP) was formed as a representative society of interventional pulmonologists based in North America. [ 7 ]  This organization also publishes a journal, namely the  Journal of Bronchology and Interventional Pulmonology . [ 8 ]  The World Association for Bronchology was founded by Dr. Ikeda in 1978 and renamed as the World Association for Bronchology and Interventional Pulmonology (WABIP) in 2010. [ 9 ]  It holds a biennial scientific meeting known as the World Congress for Bronchology and Interventional Pulmonology. The Association for Interventional Pulmonology Program Directors (AIPPD), dedicated to the advancement of IP education in the United States, was created in 2012. [ 10 ]


In addition to basic bronchoscopic and pleural procedures that are performed by a general pulmonologist, an interventional pulmonologist may perform the following advanced procedures:


For purposes of formal training in interventional pulmonology, dedicated training programs only became available in the early 21st century. The first dedicated program was a 12-month advanced fellowship offered by Dr. Beamis at  Lahey Clinic  in  Boston . [ 11 ]  Currently, there are over 30 IP  fellowship  programs across the country. [ 10 ]  However, training programs have varied considerably in terms of the breadth and depth of procedural training that they offer. [ 12 ]


To address the issue of inconsistent IP training across fellowship programs, representative members from five professional organizations (AABIP, AIPPD, ACCP, ATS, and APCCMPD) jointly published a list of minimum standards required by July 2019 in order for IP fellowship programs to receive formal accreditation from the AABIP and AIPPD. [ 13 ]


To be eligible for this fellowship, applicants must first complete a three-year fellowship in pulmonary &  critical care medicine . Most of these programs select one to two fellow(s) per year, applying though the Interventional Pulmonary Fellow Application Service (IPFAS©). As with most other medical specialties and subspecialties across the United States, applicants are matched to programs through the  National Resident Matching Program  (NRMP, or the “Match”). [ 10 ]


Interventional radiology  ( IR ) is a medical specialty that performs various  minimally-invasive procedures  using medical imaging guidance, such as  x-ray fluoroscopy ,  computed tomography ,  magnetic resonance imaging , or  ultrasound . IR performs both diagnostic and therapeutic procedures  through very small incisions  or  body orifices . Diagnostic IR procedures are those intended to help make a  diagnosis  or guide further medical treatment, and include image-guided biopsy of a tumor or injection of an  imaging contrast agent  into a hollow structure, such as a  blood vessel  or a  duct . By contrast,  therapeutic  IR procedures provide direct treatment—they include catheter-based medicine delivery, medical device placement (e.g., stents), and angioplasty of narrowed structures.


The main benefits of IR techniques are that they can reach the deep structures of the body through a  body orifice  or tiny incision using  small needles and wires . This decreases risks, pain, and recovery compared to  open procedures .  Real-time  visualization also allows precision guidance to the abnormality, making the procedure or diagnosis more accurate.  These benefits are weighed against the additional risks of lack of immediate access to internal structures (should bleeding or a perforation occur), and the risks of  radiation exposure  such as cataracts and cancer.


Interventional radiology is a set of techniques that allows access to the internal structures of the body through  body orifices  or very small incisions and guidance with  medical imaging .  Regardless of the reason for the intervention, the procedure will likely use common elements such as a  puncture needle  (to pass through the skin),  guidewires  (to guide through structures such as blood vessels or the biliary or urinary systems), a sheath (which slides over the guidewire and holds the path open without injuring it), and  catheters  (that allow fluids to be pushed through them). [ 1 ]


Also common to all intervention radiology procedures are the medical imaging machines that allow the healthcare provider to see what is occurring within the body.  Some use X-rays (such as  CT  and  fluoroscopy ) and some do not (such as  ultrasound  and  MRI ). [ 1 ]   In each case, the images created may be modified by computer to better visualize the structures as is in the case with  digital subtraction angiography , CT and MRI, or the display of the images improved with  virtual reality  or  augmented reality  presentation. [ 2 ]


Vascular


Biliary intervention [ 11 ]


Catheter placement


Ablative [ 13 ] [ 14 ]


Genitourinary [ 16 ]


The treatment of  gastrointestinal hemorrhage  can range anywhere from monitoring an asymptomatic bleed to supporting and maintaining the hemodynamic function of the patient. The role for the interventional radiologist is to offer patients an image-guided, minimally invasive procedure to alleviate a condition that could be otherwise be potentially life-threatening. [ 17 ]


The avenue for the interventional radiologist to dictate the clinical course of a GI bleed is largely influenced by location of bleed, overall patient health and other conditions the patient may have, most notably heart and liver functions. For most cases, collaboration between the gastroenterologist and interventional radiologist optimizes patient outcome but again, is largely dictated by anatomical location of the GI bleed. If a patient is evaluated and determined to be a candidate for an interventional procedure, then the bleed is often treated by embolization. Embolization is a process in which the interventional radiologist accesses the culprit bleeding vessel via a small catheter and interrupts blood flow to the site of bleeding via various mechanisms. Side effects of this procedure are minimal but there is a risk of bleeding and infection—though much less than the equivalent surgical procedure. When successful, the procedure often eliminates the bleed and patients can walk after a few hours of rest. [ 18 ]


A transjugular intrahepatic portosystemic shunt (TIPS) is a procedure an interventional radiologist performs to create a shunt (essentially, a new conduit allowing for blood flow) between the hepatic inferior vena cava and the portal vein, a vessel that returns blood from the intestines to the liver. The portal vein is the site where hypertension (high blood pressure) can produce a myriad of deleterious effects throughout the liver and small or large intestine. [ 19 ]


Primarily, a TIPS functions to alleviate two different conditions: an emergent/life-threatening GI bleed or ascites (excessive abdominal fluid) caused by too high of blood pressure in the portal vein that is otherwise uncontrolled by diet and medications. [ citation needed ]


The workup for the procedure is straightforward and the interventional radiologist performing the procedure often orders several tests to assess how well the patient will tolerate the procedure. These are often simple blood tests, and an ultrasound of the heart and liver. The procedure is often well tolerated and can result in a permanent reduction or elimination of symptoms. The procedure can take anywhere between 15 minutes to an hour and has lower risks of bleeding or infection compared to an equivalent surgical procedure. [ 19 ]


A TIPS may cause temporary confusion or worsening of liver/heart function. The degree of these two side effects largely depends on the health of the patient's heart and liver prior to the procedure and the risk-benefits of the procedure must be thoroughly discussed with their interventional radiologist before beginning. If the post-procedural consequences are more troublesome to the patient than their initial symptoms the artificial conduit created by the procedure can be reversed if the post-procedural side effects outweigh those caused by the prior conditions. [ 19 ]


In addition to normal liver tissue, the liver has three main vessels traversing it: arteries, veins and bile ducts. While bile is made in the liver and stored in the gallbladder, the bile eventually passes into the GI tract through the hepatic, cystic and common bile ducts.  Any condition that prevents the normal flow of bile from the liver, through these bile vessels and into the GI tract can cause a condition called  jaundice . [ citation needed ]


While jaundice can be caused by a few viruses that the human body can naturally clear, jaundice in the setting of an obstruction is usually caused by a cancer and can result in intolerable itching and a worsening of liver function that can be life-threatening. Depending on a patient's condition, this type of obstructive jaundice can be alleviated with surgery or chemotherapy but if these measures fail to restore proper flow of bile, an interventional radiologist can perform a procedure called a percutaneous transhepatic cholangiography (PTC). [ 20 ]


A PTC is an outpatient procedure lasting anywhere from 15 minutes to an hour where an interventional radiologist accesses the patient's bile duct system with a needle through the skin and liver under imaging guidance. Using fluoroscopy (essentially an X-ray camera) to guide a wire (followed by a catheter over the wire) through the bile duct system and into the GI tract, essentially restoring the normal flow of bile. If the patient's GI tract cannot be accessed due to the obstruction, the catheter can be placed to drain the bile duct system into a bag that the patient can wear during daily activities. Risks of this procedure include bleeding and infection but these are much lower than an equivalent surgical procedure. [ 20 ]


Benign prostatic hyperplasia , or BPH, is a noncancerous condition that commonly affects men over the age of 50. The prostate gland enlarges and compresses the adjacent urethra, making it difficult for men to control frequency and/or urgency of urination. [ 21 ]  First-line therapy involves medication, though long-term treatment for symptoms that are persistent despite medical optimization typically involves transurethral resection of the prostate (TURP) as the "gold standard" of care. However, TURP can lead to urinary incontinence or permanent male infertility and may not be the ideal procedure for a certain subset of patients. [ 22 ]  For those reasons, a physician may recommend undergoing a treatment known as prostate artery embolization (PAE). [ citation needed ]


Patients typically go home the same day as the procedure and can expect to feel some symptom relief in a matter of days. Though rare, risks of PAE include unintentional embolization of nearby blood vessels, which can result in loss of blood flow to surrounding areas of the bladder or rectum. [ 22 ]


Data suggests that TURP may have higher rates of symptom resolution at one and six months, but PAE appears to provide lower risks of complications more commonly associated with surgery, such as infection. [ 22 ]


Kidney stones  can be present along any part of the course of the urinary tract from the kidneys to the urethra. The most common symptoms, whether in men or women, are sudden onset, intense flank pain accompanied by blood in the urine. Most kidney stones pass spontaneously, but larger ones (greater than 5 mm) are less likely to, and can cause severe pain or infection. [ 23 ]


The interventional radiologist plays a large clinical role in the treatment of kidney stones that are unlikely to pass on their own. The gold standard of treatment for these types of stones is surgical removal. However, some patients have an infected stone and are simply too ill for an operative surgical removal. In these instances, the mainstay of IR treatment is a percutaneous nephrostomy tube. [ 24 ]  This is a procedure where a small caliber catheter is placed through the skin and into the urinary collecting system upstream of the stone. This procedure not only drains any infection, often bringing about a precipitous improvement in the patient's symptoms but also diverts urine—thus giving the patient more time to recover before definitive surgical treatment. [ 25 ]


A  varicocele  is defined as an enlargement of the veins within the scrotum, most commonly occurring on the left side due to anatomical reasons. When this happens, blood can stagnate within these dilated veins and cause temperature fluctuations within the testicle itself. The exact cause to this condition remains unknown and an ill-favored sequela can be male  infertility . [ 26 ]


The mainstay of treatment for this condition within the field of interventional radiology is varicocele embolization. An embolization, within the context of this procedure, results in the interruption of venous blood flow. The interruption of blood flow abates venous dilation of blood that can lead to impaired testicular temperature regulation and theoretically improve infertility. [ 27 ]  The physician accesses the dilated scrotal veins with a small catheter via a vein in the groin and embolizes the varicocele. Patients often tolerate this procedure well and are able to return home the same day. [ citation needed ]


About 87% of all strokes are  ischemic strokes , in which blood flow to the brain is blocked. [ 28 ]  A clot-busting medication such as  tissue plasminogen activator  (t-PA) can be used in a controlled hospital setting to dissolve the clot and help restore blood flow to the damaged area of the brain. Certain patients with an acute ischemic stroke may be candidates for endovascular therapy. [ 29 ]  Endovascular therapy is a procedure performed by neurointerventionalists to remove or dissolve the  thrombus  (clot) and restore blood flow to parts of the brain. Using a catheter that is directed through the blood vessels in the arm or leg up to the brain, the interventionalist can remove the thrombus or deliver drugs to dissolve the thrombus. [ 29 ]  These procedures are referred to as  mechanical thrombectomy  or  thrombolysis , and several factors are considered before the procedure is completed. [ citation needed ]


People who may be eligible for endovascular treatment have a large vessel occlusion, which means the thrombus is in an artery that is large enough to reach and there are no contraindications such as a hemorrhagic stroke (bleeding in the brain), elapsed time of greater than six hours since onset of symptoms, or greater than 24 hours in special cases. Hospitals with comprehensive stroke centers are equipped to treat patients with endovascular care. [ 30 ]


Long-term care after an ischemic stroke is focused on rehabilitation and preventing future blood clots using  anticoagulant  therapy. Patients work with specialists from fields such as  physical therapy ,  occupational therapy , and  speech therapy  to complete recovery. [ 31 ]


Although there are no clearly defined recommendations on treatment of asymptomatic aneurysms, all symptomatic unruptured brain aneurysms should be treated. Endovascular therapy is an effective treatment for select cases. [ 32 ]  During this treatment, an interventional radiologist inserts a catheter into the patient's leg and uses it to guide a coil through blood vessels to the site of the aneurysm. The coil induces clotting within the aneurysm, which reduces the risk of rupture. Multiple coils may be used depending on the size. [ 33 ]  Imaging studies ( DSA ,  CTA , or  MRA ) help characterize the aneurysm to decide the best course of treatment, whether endovascular coiling or surgical clipping. Endovascular coiling is associated with a reduction in procedural morbidity and mortality over surgical. For cases of ruptured aneurysms, emergent treatment is based on the type of aneurysm, and may use a combination of techniques. Conservative therapy focuses on minimizing modifiable risk factors with blood pressure control and smoking cessation. [ 34 ]


Arteriovenous malformations (AVMs) are abnormal blood vessel structures in which an artery connects to a vein via an abnormal channel. This creates a high flow system that puts the vessel at risk of rupture. Ruptured AVMs require emergency management of the patient; unruptured AVMs require expert consultation to discuss the risks and benefits of treatment. [ 35 ]  Current treatment options include conservative management, surgical resection,  stereotactic radiosurgery , endovascular embolization, or combinations of these treatments. [ 36 ]   Endovascular embolization  is a technique used by neurointerventionalists in which particles, glue, or coils are lodged inside the AVM to prevent blood flow through the abnormal channel. During this treatment, an interventional radiologist guides a catheter through a blood vessel accessed from the patient's leg to the site of the AVM. The particles, glue, or coils induce clotting within the malformation, which reduces the risk of rupture. [ 37 ]


Utilizing image guidance,  local anesthetics  and/or long-acting steroid medications can be directly delivered to localized sites of pain.  The use of image guidance helps to confirm appropriate needle placement. [ 38 ]  This includes common imaging modalities used in joint injections:  ultrasound ,  fluoroscopy  and  computerized tomography  (CT).


Vertebral augmentation , which includes vertebroplasty and kyphoplasty, are similar spinal procedures in which  bone cement  is injected through a small hole in the skin into a fractured  vertebra  to try to relieve  back pain  caused by a vertebral  compression fractures . It was found ineffective in treating  osteoporosis -related compression fractures of the spine. [ 53 ] [ 54 ]  The people in both the experimental and placebo groups reported improvement in their pain, suggesting that the benefit is related to the  placebo effect . As of 2019 [update] , routine use is thus not recommended. [ 55 ]


Interventional oncology (IO) procedures are commonly applied to treat primary or  metastatic  cancer. IO treatments may be also offered in combination with surgery, systemic chemotherapy/immunotherapy, and radiation therapy to augment the therapeutic outcome. A variety of interventional oncological treatments for tumors arise:


Vascular disease  refers to disorders of the vasculature or  circulatory system , most commonly involving the  arteries ,  veins  and  lymphatics . The symptoms related to vascular disease can range from asymptomatic, bothersome symptoms or limb- and/or life-threatening conditions.


Vascular and interventional radiologists are at the forefront of treating a wide variety of vascular diseases.


Since its development by  Charles Dotter  when he did a percutaneous peripheral vascular revascularization procedure for the first time on January 16, 1964, on Laura Shaw, vascular and interventional radiology (commonly interventional radiology or IR) distinguished itself from earlier approaches to vascular disease by the use of medical imaging to guide endovascular therapies (fixing this from inside the vessel). [ 75 ] [ 76 ]  The  Seldinger technique  is the basic principle that underlies endovascular procedures. Briefly, this involves using a needle to puncture a target vessel, then using a series of small medical guidewires and catheters to pass various tools inside for treatment. [ 77 ] [ 78 ]  When these minimally-invasive techniques can be used, patients avoid the need for larger surgical exposure to treat diseased vessels. Though numerous factors can affect patient's post-operative course, in general an endovascular approach is associated with a more rapid recovery time compared to a traditional open vascular surgery. [ citation needed ]


Many endovascular procedures have since been developed and refined. Numerous tools are at the disposal of modern vascular and interventional radiologists to perform these procedures, and developing new tools is a burgeoning focus of international research.


While some interventional radiology endovascular procedures are highly specialized, a few standard techniques apply to most:


The goal of endovascular therapy is to  revascularize  an affected or diseased vessel.


Arteries  are the component of the  circulatory system  that carry oxygenated blood away from the  heart  to the vital  organs  and  extremities . Arteries have relatively thick, muscular walls, composed of multiple layers, because they transport freshly oxygenated blood through the body at relatively high pressures. Arterial diseases can affect one or multiple layers of the artery wall.


The  aorta  is the largest artery in the body, and the major aortic branches continue to divide multiple times, giving way to smaller arteries, muscular  arterioles  and thin-walled  capillaries . In contrast to arteries, capillaries have thin single-layered walls, so oxygen and nutrients can be exchanged with tissues in capillary beds before the de-oxygenated blood is carried away by the venous system.


Perfusion  refers to the flow of oxygen and nutrient rich blood into the capillary beds of the muscles and organs, this is critical for their function. The lack of adequate perfusion is referred to as  ischemia  and is typically the cause of symptoms related to vascular disease. The goal of revascularization therapies, whether endovascular or surgical, is to re-establish or optimize perfusion and stop ischemia.


Atherosclerosis  refers to a progressive narrowing of the arteries due to  atheroma , derived from the Greek word for 'gruel, porridge'. Atheromatous plaque is a mixture of fat and inflammatory debris that sticks to the inner walls of an artery. Plaque can be soft or become firm as it accrues layers of calcium, a byproduct of chronic inflammation. Atherosclerosis has no single cause but many recognized risk factors. Some risk factors are modifiable, and others are not. Age and genetic predispositions are examples of non-modifiable risk factors. Medical management of atherosclerosis aims to address the many other known modifiable risk factors, such as smoking, diet, and exercise, as well as blood sugar levels in patients with diabetes. Using medications to control blood pressure and cholesterol have also been shown beneficial.


Atherosclerosis is described, evaluated, and treated differently depending on the affected artery, as described below. However, multiple studies have shown strong correlations between the different types of atherosclerosis. [ 85 ] [ 86 ] [ 87 ]  In particular, patients with peripheral arterial disease have an increased risk of coronary artery disease, and severe peripheral artery disease symptoms can be a predictor of cardiac-related mortality. The majority of patients begin to develop symptoms from ischemia around middle age, even though vessel narrowing can develop silently and slowly over decades. Unfortunately, sudden cardiac death or stroke can be a patient's first sign of vascular disease. Therefore, controlling risk factors is crucial in those with known atherosclerosis to prevent progression of disease, and screening is recommended by some vascular disease specialists for those at increased risk, such as those with diabetes, smoking or a strong family history of cardiovascular disease.


Screening tests typically use the non-invasive evaluation called the  ankle–brachial index , which compares the blood pressure between the arm and the ankle. This can help detect narrowing in the major vessels of the chest, abdomen, pelvis, and legs. CT scans of the heart with evaluations of coronary artery calcium are also used in some instances to stratify risk of coronary artery disease.