Non-uniform illumination correction  is a technique that adjusts for non-uniform illumination in fundoscopic image. Non-uniform illumination can be a potential error in automated detection of diabetic retinopathy because of changes in statistical characteristics of image. [ 77 ]  These changes can affect latter processing such as feature extraction and are not observable by humans. Correction of non-uniform illumination (f') can be achieved by modifying the pixel intensity using known original pixel intensity (f), and average intensities of local (λ) and desired pixels (μ) (see formula below). [ 82 ]  Walter-Klein transformation is then applied to achieve the uniform illumination. [ 82 ]  This technique is the least used pre-processing method in the review from 2014.


f
 ′

 =
 f
 +
 μ
 −
 λ

 {\displaystyle f'=f+\mu -\lambda }


Morphological operations  is the second least used pre-processing method in 2014 review. [ 77 ]  The main objective of this method is to provide contrast enhancement, especially darker regions compared to background.


After pre-processing of funduscopic image, the image will be further analyzed using different computational methods. However, the current literature agreed that some methods are used more often than others during vessel segmentation analyses. These methods are SVM, multi-scale, vessel-tracking, region growing approach, and model-based approaches.


Support vector machine  is by far the most frequently used classifier in vessel segmentation, up to 90% of cases. [ citation needed ]  SVM is a supervised learning model that belongs to the broader category of pattern recognition technique. The algorithm works by creating a largest gap between distinct samples in the data. The goal is to create the largest gap between these components that minimize the potential error in classification. [ 83 ]  In order to successfully segregate blood vessel information from the rest of the eye image, SVM algorithm creates support vectors that separate the blood vessel pixel from the rest of the image through a supervised environment. Detecting blood vessel from new images can be done through similar manner using support vectors. Combination with other pre-processing technique, such as green channel filtering, greatly improves the accuracy of detection of blood vessel abnormalities. [ 77 ]  Some beneficial properties of SVM include [ 83 ]


Multi-scale  approach is a multiple resolution approach in vessel segmentation. At low resolution, large-diameter vessels can first be extracted. By increasing resolution, smaller branches from the large vessels can be easily recognized. Therefore, one advantage of using this technique is the increased analytical speed. [ 75 ]  Additionally, this approach can be used with 3D images. The surface representation is a surface normal to the curvature of the vessels, allowing the detection of abnormalities on vessel surface. [ citation needed ]


Vessel tracking  is the ability of the algorithm to detect "centerline" of vessels. These centerlines are maximal peak of vessel curvature. Centers of vessels can be found using directional information that is provided by Gaussian filter. [ citation needed ]  Similar approaches that utilize the concept of centerline are the skeleton-based and differential geometry-based. [ 75 ]


Region growing  approach is a method of detecting neighboring pixels with similarities. A seed point is required for such method to start. Two elements are needed for this technique to work: similarity and spatial proximity. A neighboring pixel to the seed pixel with similar intensity is likely to be the same type and will be added to the growing region. One disadvantage of this technique is that it requires manual selection of seed point, which introduces bias and inconsistency in the algorithm. [ 75 ]  This technique is also being used in optic disc identification. [ citation needed ]


Model-based  approaches employ representation to extract vessels from images. Three broad categories of model-based are known: deformable, parametric, and template matching. [ 75 ]  Deformable methods uses objects that will be deformed to fit the contours of the objects on the image. Parametric uses geometric parameters such as tubular, cylinder, or ellipsoid representation of blood vessels. Classical snake contour in combination with blood vessel topological information can also be used as a model-based approach. [ 84 ]  Lastly, template matching is the usage of a template, fitted by stochastic deformation process using Hidden Markov Mode 1.


Automation of medical diagnosis labor (for example,  quantifying red blood cells ) has some historical precedent. [ 85 ]  The  deep learning  revolution of the 2010s has already produced AI that are more accurate in many areas of visual diagnosis than radiologists and dermatologists, and this gap is expected to grow.


Some experts, including many doctors, are dismissive of the effects that AI will have on medical specialties.


In contrast, many economists and artificial intelligence experts believe that fields such as radiology will be massively disrupted, with unemployment or downward pressure on the wages of radiologists; hospitals will need fewer radiologists overall, and many of the radiologists who still exist will require substantial retraining.  Geoffrey Hinton , the "Godfather of deep learning", argues that in light of the likely advances expected in the next five or ten years, hospitals should immediately stop training radiologists, as their time-consuming and expensive training on visual diagnosis will soon be mostly obsolete, leading to a glut of traditional radiologists. [ 86 ] [ 87 ]


An op-ed in  JAMA  argues that pathologists and radiologists should merge into a single " information specialist " role, and state that "To avoid being replaced by computers, radiologists must allow themselves to be displaced by computers." Information specialists would be trained in " Bayesian logic ,  statistics ,  data science ", and some  genomics  and  biometrics ; manual visual pattern recognition would be greatly de-emphasized compared with current onerous radiology training. [ 88 ]


Computer-aided simple triage  ( CAST ) are computerized methods or systems that assist physicians in initial interpretation and classification of medical images. CAST is a sub-class of  computer-aided diagnosis  (CAD). CAST  software  systems perform a fully automatic initial  triage  (classification) of diagnostic  medical imaging  studies. CAST is primarily intended for  emergency   diagnostic imaging , where a prompt  diagnosis  of critical, life-threatening condition is required. [ 1 ]


Computer-aided simple triage (CAST) is a combination of  computer-aided diagnosis  (CAD) and  simple triage and rapid treatment  (START).
CAST performs a fully automatic initial interpretation of a study – a "wet read". Studies are automatically classified into some meaningful categories, e.g. positive/negative, critical/minor/normal, difficult/simple/non-diagnostic, etc. [ 1 ]


CAST is primarily intended for  emergency  diagnostic imaging. Unlike traditional CAD, mainly used to detect malignant lesions, CAST deals with acute, life-threatening conditions, when a prompt diagnosis is time
critical. While the primary goal of the traditional  CAD  is improving the diagnostic accuracy of a human reader, the CAST addresses two other problems:


As with the traditional CAD, CAST does not substitute the physician. It only alerts about the possibility of acute, critical condition, or suggests that the study is free of severe disease. In both cases, the diagnosis should be verified by a trained physician.
The clinical benefit is achieved:


Traditional CAD system usually plays the role of a "second reader" and is used  after or during  the interpretation
performed by physician. CAST, on the other hand, analyzes the study  before  the physician, in a background, fully automatic mode. By the time physician comes to read the study, the initial triage or "wet read" prepared by CAST is already available. CAST system can send a message to a physician to report an urgent case requiring immediate attention.


Like any CAD system, CAST, in general, cannot guarantee 100% diagnostic accuracy.
Since CAST operates in a fully automated mode, the system is expected to exhibit very high  sensitivity  – usually above 90%. Moreover, the need to provide a diagnosis at "per study" level dictates stringent requirements for CAST  specificity  as well. The average of one or more  false alarms  per study, tolerable for a traditional CAD, is not acceptable for CAST, as almost every study would be reported as positive. Therefore, for most clinical applications, CAST specificity should be higher than 60-70% to make it useful.


Since CAST operates in a fully automatic mode, it should be able to deal with any study, regardless of image quality, patient anatomy, etc. Therefore, CAST systems should implement a quality control mechanism to ensure the high confidence level of the diagnosis. If the system decides (based on the evaluated image quality, detected  artifacts , anatomical anomalies, etc.) that no reliable diagnosis can be automatically achieved, it reports a failure.


CAST approach is applicable for the automatic detection of acute, life-threatening conditions from diagnostic medical images, such as:


CAST system can analyze images acquired with various modalities, including  x-ray ,  CT ,  MRI ,  ultrasound  and others.


CAST system is available for the detection of significant (>50%)  coronary   stenosis  in coronary  CT angiography  (cCTA) studies. The system exhibits "per study"  specificity  of 60–70%, while keeping the  sensitivity  above 90%. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ]
It can be used for chest pain patient triage in emergency room.


A deep learning system is available for automatic detection of  Intracranial Hemorrhages  in acute care settings. [ 8 ]


Contrast-induced nephropathy  (CIN) is a purported form of  kidney damage  in which there has been recent exposure to  medical imaging contrast  material without another clear cause for the acute kidney injury.


Despite extensive speculation, the actual occurrence of contrast-induced nephropathy has not been demonstrated in the literature. [ 1 ]  Analysis of  observational studies  has shown that radiocontrast use in  CT scanning  is not  causally  related to changes in  kidney function . [ 2 ]


Given the increasing doubts about the contribution of radiocontrast to acute kidney injury, the  American College of Radiology  has proposed the name contrast-associated acute kidney injury (CA-AKI) (formerly referred to as post-contrast acute kidney injury; PC-AKI) because it does not imply a  causal role , with the name contrast-induced acute kidney injury (CI-AKI) (formerly referred to as contrast-induced nephropathy; CIN) reserved for the rare cases where radiocontrast is likely to be causally related. [ 3 ]


There are multiple risk factors of contrast-induced nephropathy, whereof a 2016 review emphasized  chronic kidney disease ,  diabetes mellitus ,  high blood pressure , reduced  intravascular volume , and  old age . [ 4 ]


European guidelines classify a pre-existing decreased  kidney function  to be a risk factor of contrast-induced nephropathy in the following cases: [ 5 ]


To calculate  estimated GFR  (a measure of kidney function) from creatinine, European guidelines use the CKD-EPI formula in adults ≥ 18 years, and the revised Schwartz formula in children. [ 5 ]  Swedish guidelines recommends no specific formula in children because of lack of evidence, but on the other hand recommends GFR based on  cystatin C  rather than creatinine in those with abnormal  muscle mass ,  liver failure , or  cirrhosis . [ 5 ]


The Mehran score is a  clinical prediction rule  to estimate probability of CIN which includes the following risk factors: systolic  blood pressure  <80 mm Hg for at least one hour requiring  inotropic  support,  intra-aortic balloon pump ,  congestive heart failure  with  New York Heart Association Functional Classification  class III or worse, history of  pulmonary edema , age >75 years,  hematocrit  level <39% for men and <35% for women,  diabetes mellitus , contrast media volume, decreased kidney function (serum creatinine level >1.5 g/dL or decreased estimated  glomerular filtration rate ). [ 6 ] [ 7 ]


European guidelines include the following procedure-related risk factors: [ 5 ]


Swedish guidelines list the following additional risk factors: [ 5 ]


The main alternatives in people with a risk of contrast-induced nephropathy are: [ citation needed ]


According to European guidelines, the ratio of the contrast dose (in grams of iodine) divided by the absolute estimated  glomerular filtration rate  (GFR) should be less than 1.1 g/(ml/min) for intra-arterial contrast medium administration with first-pass renal exposure (not passing lungs or peripheral tissue before reaching the kidneys). [ 5 ]  Swedish guidelines are more restrictive, recommending a ratio of less than 0.5 g/(ml/min) in patients with risk factors and irrespective of route of administration, and even more caution in first-pass renal exposure. [ 5 ]


Hydration by  drinking  or intravenous  volume expander , either before or after contrast administration, decreases the risk of contrast-induced nephropathy. [ 8 ]  Evidence also supports the use of  N-acetylcysteine  with intravenous saline among those getting low molecular weight contrast. [ 9 ] [ dubious  –  discuss ]  The use of  statins  with N-acetylcysteine and intravenous saline is also supported. [ 9 ]


CIN is classically defined as a  serum creatinine  increase of at least 25% and/or an absolute increase in serum creatinine of 0.5 mg/dL [ 17 ]  after using iodine  contrast agent  without another clear cause for acute kidney injury, [ 4 ]  but other definitions have also been used. [ 2 ]


The  American College of Radiology  recommends the usage of the AKIN criteria for the diagnosis of CIN or PC-AKI. The AKIN criteria states that the diagnosis is made if within 48 hours from intravascular  contrast medium  exposure one of the following occurs: [ 18 ]


The mechanism of contrast-induced nephropathy is not entirely understood, but is thought to include a combination of direct  renal tubule  damage from the contrast agent and reductions in blood flow to areas of the kidney. [ 19 ]  The contrast agent directly damages renal tubule cells by a variety of mechanisms, one proposed mechanism is by causing changes in cell polarity. The  sodium potassium pump  (also known as the Na+/K+ ATPase) is redistributed from the basal surface to the luminal surface of renal tubule cells. [ 19 ]  This causes sodium to be transported into the lumen where it is delivered to the distal renal tubule. This sodium load being delivered to the distal renal tubule leads to renal vasoconstriction via tubuloglomerular feedback, with the vasoconstriction and restriction of blood flow leading to injury of tubular cells. [ 19 ]  Contrast agents cause damage to renal tubular cells in other ways specific to the type of contrast agent, leading to  apoptosis  and necrosis of the tubular cells. [ 19 ]  The damaged renal tubular cells detach from the basement membrane and accumulate in the tubules which causes an increase in tubular pressure, reduced glomerular filtration rate and luminal blockage. [ 19 ]  The viscosity of contrast filtered into the tubule may also contribute to increases in tubular pressure. [ 19 ]


Contrast agents may also cause renal tubular injury by causing renal vasoconstriction mediated by inhibition of vasodilators such as  nitric oxide  and  prostaglandins  and activation of  endothelin . This renal vasoconstriction, along with increases in blood viscosity caused by the contrast agents themselves, leads to renal vasoconstriction and reduced blood flow to metabolically active areas of the kidneys thus causing kidney damage. [ 19 ]  Changes in blood osmolality due to the contrast agents may lead to reduced red blood cell elasticity, thus leading to microthrombi development in the small blood vessels of the kidney thus further reducing glomerular blood flow. [ 19 ]


It is unclear if CIN causes persisting decline in renal function since few studies has followed patients for more than 72 hours. [ 18 ]  In one meta-analysis the decline in renal function was shown to persist in 1.1 % of the patients with CIN. [ 20 ]


Doubts regarding the significance of the phenomenon appeared in the scientific literature. Several studies have shown that intravenous contrast material administration was not associated with excess risk of  acute kidney injury , dialysis, or death, even among patients with comorbidities reported to predispose them to nephrotoxicity. [ 1 ]  Moreover, hydration, the most established prevention measure to prevent contrast-induced nephropathy was shown to be ineffective in the POSEIDON trial, [ 21 ]  raising further doubts regarding the significance of this disease state. [ 22 ]  A meta-analysis of 28 studies of AKI after CT with radiocontrast showed no causal relationship between the use of radiocontrast and AKI. [ 2 ]


Digital X-ray radiogrammetry   is a method for measuring  bone mineral density  (BMD). Digital X-ray radiogrammetry is based on the old technique of  radiogrammetry . In DXR, the  cortical  thickness of the three middle  metacarpal bones  of the hand is measured in a digital X-ray image. [ 1 ]  Through a geometrical operation the thickness is converted to bone mineral density. The BMD is corrected for  porosity  of the bone, estimated by a texture analysis performed on the cortical part of the bone. [ 2 ] [ 3 ]


Like other technologies for estimating the bone mineral density, the outputs are an areal BMD value, a  T-score  and a  Z-score  for assessing  osteoporosis  and the risk of bone fracture. [ 4 ]


Digital X-ray radiogrammetry is primarily used in combination with  digital mammography  for osteoporosis screening, where same mammography machine that is used to acquire breast X-ray images is also used to acquire a hand image for BMD measurement. Due to high  precision , DXR is also used for monitoring change in bone mineral density over time. [ 5 ]  Recent studies have suggested that DXR is a promising alternative for DXA for determining low bone quality in children with suspected secondary low bone quality or osteoporosis. [ 1 ]


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


Dual X-ray absorptiometry and laser technique  (DXL) in the area of  bone density studies  for  osteoporosis  assessment is an improvement to the  DXA Technique , adding an exact laser measurement of the thickness of the region scanned. The addition of object thickness adds a third input to the two  x-ray  energies used by DXA, better solving the equation for bone and excluding more efficiently these soft tissues components.


The body consists of three main components:  bone mineral , lean soft tissue (skin, blood, water and skeletal muscle) and  adipose tissue  (fat and yellow bone marrow). These different components have different  x-ray attenuating  properties. The standard in bone mineral density scanning developed in the 1980s is called  Dual X-ray Absorptiometry , known as DXA. The DXA technique uses two different x-ray energy levels to estimate  bone density . DXA scans assume a constant relationship between the amounts of lean soft tissue and adipose tissue. This assumption leads to measurement errors, with an impact on accuracy as well as precision.


To reduce soft-tissue errors in DXA, DXL technology was developed in the late 1990s by a team of Swedish researchers led by Prof. Ragnar Kullenberg. With DXL technology, the  region of interest  is scanned using low and high energy x-rays as with a DXA scan. The improvement to DXA with DXL is that, for each pixel scanned by DXA, the exact  thickness of the measured object is also measured using lasers. The DXL results allow for a more accurate estimation of bone density by using three separate inputs (low and high x-ray energies plus thickness) rather than two for each pixel in the measuring region.


Using the DXL technique, for each measuring point (or pixel) the following equations apply:


N1 = N01⋅exp(-(νb1⋅tb⋅σb + νs1⋅ts⋅σs + νf1⋅tf⋅σf))


N2 = N02⋅exp(-(νb2⋅tb⋅σb + νs2⋅ts⋅σs + νf2⋅tf⋅σf))


T = tb + ts + tf


Where:


tb * σb is the unknown bone density that one wants to calculate, e.g. areal mass (g/cm2).


The DXL technique is used in the bone densitometry system  DXL Calscan , manufactured and marketed by the company Demetech AB, Täby, Sweden. Many published studies have evaluated the DXL technique using the DXL Calscan system, which scans the subject's heel. Several published fracture studies have shown that heel scans using DXL Calscan have an ability to predict fractures as well or better than the DXA technique scanning the hip. [ 1 ] [ 2 ] [ 3 ] [ 4 ]


Dual-energy X-ray absorptiometry  ( DXA , or  DEXA [ 1 ] ) is a means of measuring  bone mineral density  (BMD) using  spectral imaging . Two  X-ray  beams, with different  energy levels , are aimed at the patient's  bones . When  soft tissue  absorption is subtracted out, the  bone mineral density  (BMD) can be determined from the absorption of each beam by bone. Dual-energy X-ray absorptiometry is the most widely used and most thoroughly studied bone density measurement technology.


The DXA scan is typically used to diagnose and follow  osteoporosis , as contrasted to the nuclear  bone scan , which is sensitive to certain metabolic diseases of bones in which bones are attempting to heal from infections, fractures, or tumors. It is also sometimes used to assess  body composition .


Soft tissue and bone have different  attenuation coefficients  to X-rays.  A single X-ray beam passing through the body will be attenuated by both soft tissue and bone, and it is not possible to determine, from a single beam, how much attenuation was attributable to the bone.  However, the attenuation coefficients vary with the energy of the X-rays, and, crucially, the ratio of the attenuation coefficients also varies.  DXA uses two energies of X-ray.  The difference in total absorption between the two can be used, by suitable weighting, to subtract out the absorption by soft tissue, leaving just the absorption by bone, which is related to bone density.


One type of DXA scanner uses a  cerium  filter with a  tube voltage  of 80  kV , resulting in effective photon energies of about 40 and 70  keV . [ 2 ]  There is also a DXA scanner type using a  samarium  filter with a tube voltage of 100 kV, resulting in effective energies of 47 and 80 keV. [ 2 ]  Also, the tube voltage can be continuously switched between a low (for example 70 kV) and high (for example 140 kV) value in synchronism with the
frequency of the electrical mains, resulting in effective energies alternating between 45 and 100 keV. [ 2 ]


The combination of  dual X-ray absorptiometry and laser  uses the laser to measure the thickness of the region scanned, allowing for varying proportions of lean soft tissue and  adipose tissue  within the soft tissue to be controlled for and improving the accuracy.


The  U.S. Preventive Services Task Force  recommends that women over the age of 65 should get a DXA scan. [ 3 ]  The date at which men should be tested is uncertain [ 3 ]  but some sources recommend age 70. [ 4 ]  At risk women should consider getting a scan when their risk is equal to that of a normal 65-year-old woman.


A person's risk can be measured using the University of Sheffield's  FRAX  calculator, which includes many different clinical risk factors including prior fragility fracture, use of  glucocorticoids , heavy smoking, excess alcohol intake, rheumatoid arthritis, history of parental hip fracture, chronic renal and liver disease, chronic respiratory disease, long-term use of phenobarbital or phenytoin, celiac disease, inflammatory bowel disease, and other risks. [ 3 ]


The World Health Organization has defined the following categories based on bone density in white women:


Bone densities are often given to patients as a T score or a Z score. A T score tells the patient what their bone mineral density is in comparison to a young adult of the same gender with peak bone mineral density. A normal T score is -1.0 and above, low bone density is between -1.0 and -2.5, and osteoporosis is -2.5 and lower. A Z score is just a comparison of what a patient's bone mineral density is in comparison to the average bone mineral density of a male or female of their age and weight.


The WHO committee did not have enough data to create definitions for men or other ethnic groups. [ 5 ]


Special considerations are involved in the use of DXA to assess bone mass in children. Specifically, comparing the bone mineral density of children to the reference data of adults (to calculate a T-score) will underestimate the BMD of children, because children have less bone mass than fully developed adults. This would lead to an over-diagnosis of  osteopenia  for children. To avoid an overestimation of bone mineral deficits, BMD scores are commonly compared to reference data for the same gender and age (by calculating a  Z-score ).


Also, there are other variables in addition to age that are suggested to confound the interpretation of BMD as measured by DXA. One important confounding variable is bone size. DXA has been shown to overestimate the bone mineral density of taller subjects and underestimate the bone mineral density of smaller subjects. This error is due to the way by which DXA calculates BMD. In DXA, bone mineral content (measured as the attenuation of the X-ray by the bones being scanned) is divided by the area (also measured by the machine) of the site being scanned.


Because DXA calculates BMD using area (aBMD: areal Bone Mineral Density), it is not an accurate measurement of true bone mineral density, which is  mass  divided by a  volume . In order to distinguish DXA BMD from  volumetric  bone-mineral density, researchers sometimes refer to DXA BMD as an areal bone mineral density (aBMD). The confounding effect of differences in bone size is due to the missing depth value in the calculation of bone mineral density. Despite DXA technology's problems with estimating volume, it is still a fairly accurate measure of bone mineral content. Methods to correct for this shortcoming include the calculation of a volume that is approximated from the projected area measure by DXA. DXA BMD results adjusted in this manner are referred to as the bone mineral apparent density (BMAD) and are a  ratio  of the bone mineral content versus a  cuboidal  estimation of the volume of bone. Like the results for aBMD, BMAD results do not accurately represent true bone mineral density, since they use approximations of the bone's volume. BMAD is used primarily for research purposes and is not yet used in clinical settings.


Other imaging technologies such as  quantitative computed tomography  (QCT) are capable of measuring the bone's volume, and are, therefore, not susceptible to the confounding effect of bone-size in the way that DXA results are susceptible.


It is important for patients to get repeat BMD measurements done on the same machine each time, or at least a machine from the same manufacturer. Error between machines, or trying to convert measurements from one manufacturer's standard to another can introduce errors large enough to wipe out the sensitivity of the measurements. [ citation needed ]


DXA results need to be adjusted if the patient is taking  strontium  supplements. [ 6 ] [ better source needed ] [ 7 ]


DXA can also used to measure  trabecular bone score .


DXA is, by far, the most widely used technique for bone mineral density measurements, since it is considered to be cheap, accessible, easy to use, and able to provide an accurate estimation of bone mineral density in adults. [ 8 ]


The official position of the  International Society for Clinical Densitometry  (ISCD) is that a patient may be tested for BMD if they have a condition that could precipitate bone loss, is going to be prescribed pharmaceuticals known to cause bone loss, or is being treated and needs to be monitored. The ISCD states that there is no clearly understood correlation between BMD and the risk of a child's sustaining a fracture; the diagnosis of osteoporosis in children cannot be made using the basis of a densitometry criteria. T-scores are prohibited with children and should not even appear on DXA reports. Thus, the WHO classification of osteoporosis and osteopenia in adults cannot be applied to children, but Z-scores can be used to assist diagnosis. [ 9 ]


Some clinics may routinely carry out DXA scans on pediatric patients with conditions such as nutritional  rickets ,  lupus , and  Turner syndrome . [ 10 ]  DXA has been demonstrated to measure skeletal maturity [ 11 ]  and body fat composition [ 12 ]  and has been used to evaluate the effects of pharmaceutical therapy. [ 13 ]  It may also aid pediatricians in diagnosing and monitoring treatment of disorders of bone mass acquisition in childhood. [ 14 ]


However, it seems that DXA is still in its early days in pediatrics, and there are widely acknowledged limitations and disadvantages with DXA. A view exists [ 15 ]  that DXA scans for diagnostic purposes should not even be performed outside specialist centers, and, if a scan is done outside one of these centers, it should not be interpreted without consultation with an expert in the field. [ 15 ]  Furthermore, most of the pharmaceuticals given to adults with low bone mass can be given to children only in strictly monitored clinical trials.


Whole-body  calcium  measured by DXA has been validated in adults using  in-vivo   neutron activation  of total body calcium [ 16 ] [ 17 ]  but this is not suitable for paediatric subjects and studies have been carried out on paediatric-sized animals. [ 16 ] [ 17 ]


DXA scans can also be used to measure total  body composition  and  fat content  with a high degree of accuracy comparable to  hydrostatic weighing  with a few important caveats. [ 18 ] [ specify ]  From the DXA scans, a low resolution "fat shadow" image can also be generated, which gives an overall impression of fat distribution throughout the body. [ 19 ]  It has been suggested that, while very accurately measuring minerals and lean soft tissue (LST), DXA may provide skewed results due to its method of indirectly calculating fat mass by subtracting it from the LST and/or body cell mass (BCM) that DXA actually measures. [ 20 ]


DXA scans have been suggested as useful tools to diagnose conditions with an abnormal fat distribution, such as  familial partial lipodystrophy . [ 21 ] [ 22 ] [ 19 ]  They are also used to assess adiposity in children, especially to conduct clinical research. [ 23 ]


DXA uses X-rays to measure bone mineral density. The  radiation  dose of current DEXA systems is small, [ 24 ]  as low as 0.001  mSv , much less than a standard chest or dental x-ray. [ 25 ] [ 26 ]  However, the dose delivered by older DEXA radiation sources (that used  radioisotopes  rather than  x-ray generators ) could  be as high as 35 mGy, [ 27 ] [ 28 ] [ 29 ]  considered a significant dose by  radiological health  standards.


The quality of DXA operators varies widely. DXA is not regulated like other radiation-based imaging techniques because of its low dosage. Each US state has a different policy as to what certifications are needed to operate a DXA machine.  California , for example, requires coursework and a state-run test, whereas  Maryland  has no requirements for DXA technicians. Many states require a training course and certificate from the International Society of Clinical Densitometry (ISCD).


In Australia, regulation differs according to the applicable state or territory. For example, in Victoria, an individual performing DXA scans is required to completed a recognised course in safe use of bone mineral densitometers. [ 30 ]  In NSW and QLD a DXA technician only requires prior study in science, nursing or other related undergraduate study. The Environmental Protection Agency (EPA) oversees licensing of technicians, however, this is far from rigorous and regulation is non-existent. [ citation needed ]


Echocardiography , also known as  cardiac ultrasound , is the use of  ultrasound  to examine the  heart . It is a type of  medical imaging , using standard ultrasound or  Doppler ultrasound . [ 1 ]  The visual image formed using this technique is called an  echocardiogram , a  cardiac echo , or simply an  echo .


Echocardiography is routinely used in the diagnosis, management, and follow-up of patients with any suspected or known  heart diseases . It is one of the most widely used diagnostic imaging modalities in cardiology. It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity, location and extent of any tissue damage, and assessment of valves. An echocardiogram can also give physicians other estimates of heart function, such as a calculation of the  cardiac output ,  ejection fraction , and  diastolic  function (how well the heart relaxes).


Echocardiography is an important tool in assessing wall motion abnormality in patients with suspected cardiac disease. It is a tool which helps in reaching an early diagnosis of  myocardial infarction , showing regional wall motion abnormality. Also, it is important in treatment and follow-up in patients with  heart failure , by assessing  ejection fraction . [ 2 ] [ 3 ]


Echocardiography can help detect  cardiomyopathies , such as  hypertrophic cardiomyopathy , and dilated cardiomyopathy. The use of stress echocardiography may also help determine whether any chest pain or associated symptoms are related to heart disease.


The most important advantages of echocardiography are that it is not invasive (does not involve breaking the skin or entering body cavities) and has no known risks or side effects. [ 4 ]


Not only can an echocardiogram create ultrasound images of heart structures, but it can also produce accurate assessment of the blood flowing through the heart by Doppler echocardiography, using pulsed- or continuous-wave Doppler ultrasound. This allows assessment of both normal and abnormal blood flow through the heart. Color Doppler, as well as spectral Doppler, is used to visualize any abnormal communications between the left and right sides of the heart, as well as any leaking of blood through the valves (valvular regurgitation), and can also estimate how well the valves open (or do not open in the case of valvular stenosis). The Doppler technique can also be used for tissue motion and velocity measurement, by  tissue Doppler echocardiography .


Echocardiography was also the first ultrasound subspecialty to use intravenous contrast. Echocardiography is performed by  cardiac sonographers , cardiac physiologists (UK), or physicians trained in echocardiography.


Recognized as the "Father of Echocardiography", the Swedish physician  Inge Edler  (1911–2001), a graduate of  Lund University , was the first of his profession to apply ultrasonic pulse echo imaging in diagnosing cardiac disease, which the acoustical physicist  Floyd Firestone  had developed to detect defects in metal castings. In fact, Edler in 1953 produced the first echocardiographs using an industrial Firestone-Sperry Ultrasonic Reflectoscope. In developing echocardiography, Edler worked with the physicist  Carl Hellmuth Hertz , the son of the  Nobel laureate   Gustav Hertz  and grandnephew of  Heinrich Rudolph Hertz . [ 5 ] [ 6 ]


Health societies recommend the use of echocardiography for initial diagnosis when a change in the patient's clinical status occurs and when new data from an echocardiogram would result in the physician changing the patient's care. [ 7 ]  Diagnostic criteria for numerous cardiac diseases are based on echocardiography studies. For example, the differentiation of mild, moderate, and severe valvular disease is based upon measured criteria. Another example is the estimation of heart function by the left ventricular ejection fraction (LVEF) has vast uses including classification of heart failure and cut offs for implantation of  implantable cardioverter-defibrillators .


Health societies do not recommend routine testing when the patient has no change in clinical status or when a physician is unlikely to change care for the patient based on the results of testing. [ 7 ]  A common example of overuse of echocardiography when not indicated is the use of routine testing in response to a patient diagnosis of mild  valvular heart disease . [ 8 ]  In this case, patients are often asymptomatic for years before the onset of deterioration and the results of the echocardiogram would not result in a change in care without other change in clinical status. [ 8 ]


Echocardiography has a vast role in  pediatrics , diagnosing patients with valvular heart disease and other congenital abnormalities. An emerging branch is  fetal echocardiography , which involves echocardiography of an unborn fetus. [ citation needed ]


There are three primary types of echocardiography: transthoracic, transesophageal, and intracardic.
Stress testing utilizes tranthoracic echo in combination with an exercise modality (e.g., a treadmill).
Intravascular ultrasound is included below, but is as the name indicates more "ultrasound" than "echocardiography" as it is imaging the walls of a vessel rather than the heart.


A standard echocardiogram is also known as a transthoracic echocardiogram (TTE) or cardiac ultrasound, and it is used for rapid evaluation of a patient at their bedside. [ 9 ] [ 10 ]  In this case, the echocardiography transducer (or probe) is placed on the chest wall (or  thorax ) of the subject, and images are taken through the chest wall. This is a non-invasive, highly accurate, and quick assessment of the overall function of the heart.


TTE utilizes several "windows" to image the heart from different perspectives. Each window has advantages and disadvantages for viewing specific structures within the heart and, typically, numerous windows are utilized within the same study to fully assess the heart. Parasternal long and parasternal short axis windows are taken next to the sternum, the apical two/three/four chamber windows are taken from the apex of the heart (lower left side), and the subcostal window is taken from underneath the edge of the last rib.


TTE utilizes one- ("M mode"), two-, and three-dimensional ultrasound (time is implicit and not included) from the different windows. These can be combined with pulse wave or continuous wave Doppler to visualize the velocity of blood flow and structure movements. Images can be enhanced with "contrast" that are typically some sort of micro bubble suspension that reflect the ultrasound waves.


A transesophageal echocardiogram is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient's  esophagus  via the mouth, allowing image and Doppler evaluation from a location directly behind the heart. It is most often used when transthoracic images are suboptimal and when a clearer and more precise image is needed for assessment. This test is performed in the presence of a cardiologist, anesthesiologist, registered nurse, and ultrasound technologist. Conscious sedation and/or localized numbing medication may be used to make the patient more comfortable during the procedure.


TEE, unlike TTE, does not have discrete "windows" to view the heart. The entire esophagus and stomach can be utilized, and the probe advanced or removed along this dimension to alter the perspective on the heart. Most probes include the ability to deflect the tip of the probe in one or two dimensions to further refine the perspective of the heart. Additionally, the ultrasound crystal is often a two-dimension crystal and the ultrasound plane being used can be rotated electronically to permit an additional dimension to optimize views of the heart structures. Often, movement in all of these dimensions is needed.


TEE can be used as stand-alone procedures, or incorporated into catheter- or surgical-based procedures. For example, during a  valve replacement  surgery the TEE can be used to assess the valve function immediately before repair/replacement and immediately after. This permits revising the valve mid-surgery, if needed, to improve outcomes of the surgery.


A stress echocardiogram, also known as a stress echo, uses ultrasound imaging of the heart to assess the wall motion in response to physical stress. First, images of the heart are taken "at rest" to acquire a baseline of the patient's wall motion at a resting heart rate. The patient then walks on a treadmill or uses another exercise modality to increase the heart rate to his or her target heart rate, or 85% of the age-predicted maximum heart rate (220 − patient's age). Finally, images of the heart are taken "at stress" to assess wall motion at the peak heart rate. A stress echo assesses wall motion of the heart; it does not, however, create an image of the coronary arteries directly. Ischemia of one or more coronary arteries could cause a wall motion abnormality, which could indicate coronary artery disease. The gold standard test to directly create an image of the coronary arteries and directly assess for stenosis or occlusion is a cardiac catheterization. A stress echo is not invasive and is performed in the presence of a licensed medical professional, such as a cardiologist, and a cardiac sonographer.


Intracardiac echocardiography (ICE) is specialized form of echocardiography that uses catheters to insert the ultrasound probe inside the heart to view structures from within the heart.
ICE is often used as a part of the cardiac procedure of crossing the  interatrial septum  with a transseptal puncture to permit catheter access from the right atrium to the left atrium; alternative access to the left heart would be retrograde through the  aorta  and across the  aortic valve  into the left ventricle.


ICE has the benefit over transthoracic echocardiography in that an operator who is performing a sterile procedure can also operate the ICE catheter and it is not limited to visibility problems that can arise with transthoracic or transesophageal echo. Though, there are image quality limitations due to size constraints of the probe being limited to a catheter.


ICE is often inserted through the femoral vein and into the right atrium.
From the right atrium, visualization of the interatrial septum, all four cardiac chambers, all four valves, and the pericardial space (for an effusion) can be readily visualized.
It can also be advanced across the atrial septum into the left atrium to visualize the left atrial appendage during  left atrial appendage occlusion  device deployment.


Utilization of ICE imagery can be incorporated into the 3-D models built with  electroanatomic mapping  systems.


Intravascular ultrasound (IVUS) is a specialized form of echocardiography that uses a catheter to insert the ultrasound probe inside blood vessels. This is commonly used to measure the size of blood vessels and to measure the internal diameter of the blood vessel. For example, this can be used in a  coronary angiogram  to assess the narrowing of the coronary artery. If the catheter is retraced in a controlled manner, then an internal map can be generated to see the contour of the vessel and its branches.


The various modes describe how the ultrasound crystals are used to obtain information. These modes are common to all types of echocardiography.


A-scan or one dimensional ultrasound represents over half the standard ECHO exam.  For example, it is how aortic stenosis valve area (or any obstruction).  It is also how pressures are calculated in the heart such as right ventricle systolic pressure (RVSP).  It is usually used in the form of Doppler measurements.  There are two forms, pulse and continuous.  Pulsed allows velocities to be calculated in a specific place, but has a limited velocity range is can be used.  Continuous wave allows the velocity to be measured from zero to the fastest blood velocities a diseased heart can generate.  However, it can not tell you where in the A-scan the high velocity is coming from.  Continuous wave would be used to calculate aortic stenosis because you know the high velocity is coming from the stenosis region.  Pulsed would be used to find a ventricular septal defect where there should be no velocity across the septum and the pulsed tells you the location.


Brightness mode is often synonymous with "2D" and is very commonly used in echocardiography.


Motion mode is infrequently used in modern echocardiography. It has specific uses and has the benefit of very high temporal fidelity (e.g., measuring LV size at end diastole).


Strain rate imaging is an ultrasound method for imaging regional differences in contraction (dyssynergy) in for instance  ischemic heart disease  or dyssynchrony due to  Bundle branch block . Strain rate imaging measures either regional systolic deformation (strain) or the rate of regional deformation (strain rate). The methods used are either  tissue Doppler  or  Speckle tracking echocardiography .


Three-dimensional echocardiography (also known as  four-dimensional  echocardiography when the picture is moving) is possible using a matrix array ultrasound probe and an appropriate processing system. It enables detailed anatomical assessment of cardiac pathology, particularly valvular defects, [ 11 ]  and cardiomyopathies. [ 12 ]  The ability to slice the virtual heart in infinite planes in an anatomically appropriate manner and to reconstruct three-dimensional images of anatomic structures make it unique for the understanding of the congenitally malformed heart. [ 13 ]  Real-time three-dimensional echocardiography can be used to guide the location of  bioptomes  during right ventricular endomyocardial biopsies, placement of catheter-delivered valvular devices, and in many other intraoperative assessments. [ 14 ]


Three-dimensional echocardiography technology may feature anatomical intelligence, or the use of organ-modeling technology, to automatically identify anatomy based on generic models.  All generic models refer to a dataset of anatomical information that uniquely adapts to variability in patient anatomy to perform specific tasks. Built on feature recognition and segmentation algorithms, this technology can provide patient-specific three-dimensional modeling of the heart and other aspects of the anatomy, including the brain, lungs, liver, kidneys, rib cage, and vertebral column. [ 15 ]


Contrast echocardiography or contrast-enhanced ultrasound is the addition of an ultrasound contrast medium, or imaging agent, to traditional ultrasonography. The ultrasound contrast is made up of tiny microbubbles filled with a gas core and protein shell. This allows the microbubbles to circulate through the cardiovascular system and return the ultrasound waves, creating a highly reflective image. There are multiple applications in which contrast-enhanced ultrasound can be useful. The most commonly used application is in the enhancement of LV endocardial borders for assessment of global and regional systolic function. Contrast may also be used to enhance visualization of wall thickening during stress echocardiography, for the assessment of LV thrombus, or for the assessment of other masses in the heart. Contrast echocardiography has also been used to assess blood perfusion throughout myocardium in the case of coronary artery disease.


Echocardiography can at many times be subjective, meaning that the person reading the echo may have personal input that affects the interpretation of the findings, leading to so-called "inter-observer variability", where different echocardiographers might produce different reports when examining the same images. [ 16 ] [ 17 ]  It necessitated the development of accreditation programs around the world. The aim of such programs is to standardize the practice of echocardiography and to ensure that practitioners have the proper training prior to practicing echocardiography which will eventually limit inter-observer variability. [ 18 ]


At the European level  [ 19 ]  individual and laboratory accreditation is provided by the European Association of Echocardiography (EAE). There are three subspecialties for individual accreditation: Adult Transthoracic Echocardiography ( TTE ), Adult Transesophageal Echocardiography ( TEE ) and Congenital Heart Disease Echocardiography (CHD).


In the UK, accreditation is regulated by the British Society of Echocardiography. Accredited radiographers, sonographers, or other professionals are required to pass a mandatory exam. [ 20 ]


The "Intersocietal Accreditation Commission for Echocardiography" (IAC) sets standards for echo labs across the US. Cardiologists and sonographers who wish to have their laboratory accredited by IAC must comply with these standards. The purpose of accreditation is to maintain quality and consistency across echocardiography labs in the United States. Accreditation is offered in adult and pediatric transthoracic and transesophageal echocardiography, as well as adult stress and fetal echo. Accreditation is a two-part process. Each facility will conduct a detailed self-evaluation, paying close attention to the IAC Standards and Guidelines. The facility will then complete the application and submit actual case studies to the board of directors for review. Once all requirements have been met, the lab will receive certification. IAC certification is a continual process and must be maintained by the facility: it may include audits or site visits by the IAC. There are several states in which Medicare and/or private insurance carriers require accreditation (credentials) of the laboratory and/or sonographer for reimbursement of echocardiograms.


There are two credentialing bodies in the United States for sonographers, the  Cardiovascular Credentialing International  (CCI), established in 1968, and the  American Registry for Diagnostic Medical Sonography  (ARDMS), established in 1975. Both CCI and ARDMS have earned the prestigious  ANSI-ISO 17024  accreditation for certifying bodies from the International Organization for Standardization ( ISO ). [ citation needed ]  Accreditation is granted through the American National Standards Institute (ANSI). Recognition of ARDMS programs in providing credentials has also earned the ARDMS accreditation with the National Commission for Certifying Agencies (NCCA). The NCCA is the accrediting arm of the National Organization for Competency Assurance (NOCA).


Under both credentialing bodies, sonographers must first document completion of prerequisite requirements, which contain both didactic and hands-on experience in the field of ultrasound. Applicants must then take a comprehensive exam demonstrating knowledge in both the physics of ultrasound and the clinical competency related to their specialty. Credentialed sonographers are then required to maintain competency in their field by obtaining a certain number of Continuing Medical Education credits, or CME's.


In 2009, New Mexico and Oregon became the first two states to require licensure of sonographers. [ citation needed ]


The  American Society of Echocardiography  (ASE) is a professional organization made up of physicians, sonographers, nurses, and scientists involved in the field of echocardiography. One of the most important roles that the ASE plays is providing their recommendations through the ASE Guidelines and Standards, providing resource and educational opportunities for sonographers and physicians in the field.


There have been various institutes who are working on use of  Artificial intelligence  in Echo but they are at a very early stage and still needs full development. [ 21 ]


The most commonly used terminology in echocardiography diagnostics are:


Effective dose  is a dose quantity in the  International Commission on Radiological Protection  (ICRP) system of  radiological protection . [ 1 ]


It is the tissue-weighted sum of the  equivalent doses  in all specified tissues and organs of the human body and represents the  stochastic  health risk to the whole body, which is the  probability  of  cancer induction  and genetic effects, of low levels of  ionizing radiation . [ 2 ] [ 3 ]  It takes into account the type of radiation and the nature of each organ or tissue being irradiated, and enables summation of organ doses due to varying levels and types of radiation, both internal and external, to produce an overall calculated effective dose.


The SI unit for effective dose is the  sievert  (Sv) which represents a 5.5% chance of developing cancer. [ 4 ]  The effective dose is not intended as a measure of  deterministic  health effects, which is the  severity  of acute tissue damage that is certain to happen, that is measured by the quantity  absorbed dose . [ 5 ]


The concept of effective dose was developed by Wolfgang Jacobi and published in 1975, and was so convincing that the ICRP incorporated it into their 1977 general recommendations (publication 26) as "effective dose equivalent". [ 6 ]  The name "effective dose" replaced the name "effective dose equivalent" in 1991. [ 7 ]  Since 1977 it has been the central quantity for dose limitation in the ICRP international system of  radiological protection . [ 1 ]


According to the ICRP, the main uses of effective dose are the prospective dose assessment for planning and optimisation in radiological protection, and demonstration of compliance with dose limits for regulatory purposes. The effective dose is thus a central dose quantity for regulatory purposes. [ 8 ]


The ICRP also says that effective dose has made a significant contribution to radiological protection as it has enabled doses to be summed from whole and partial body exposure from external radiation of various types and from intakes of radionuclides. [ 9 ]


The calculation of effective dose is required for partial or non-uniform irradiation of the human body because  equivalent dose  does not consider the tissue irradiated, but only the radiation type. Various body tissues react to ionising radiation in different ways, so the ICRP has assigned sensitivity factors to specified tissues and organs so that the effect of partial irradiation can be calculated if the irradiated regions are known. [ 10 ]   A radiation field irradiating only a portion of the body will carry lower risk than if the same field irradiated the whole body. To take this into account, the effective doses to the component parts of the body which have been irradiated are calculated and summed. This becomes the effective dose for the whole body, dose quantity  E . It is a "protection" dose quantity which can be calculated, but cannot be measured in practice.


An effective dose will carry the same effective risk to the whole body regardless of where it was applied, and it will carry the same effective risk as the same amount of equivalent dose applied uniformly to the whole body.


Effective dose can be calculated for  committed dose  which is the internal dose resulting from inhaling, ingesting, or injecting radioactive materials.


The dose quantity used is:


Committed effective dose,   E( t )  is the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors  W T , where  t  is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and to age 70 years for children. [ 11 ]


Ionizing radiation deposits energy in the matter being irradiated. The quantity used to express this is the  absorbed dose , a physical dose quantity that is dependent on the level of incident radiation and the absorption properties of the irradiated object. Absorbed dose is a physical quantity, and is not a satisfactory indicator of biological effect, so to allow consideration of the stochastic radiological risk, the dose quantities equivalent dose and effective dose were devised by the  International Commission on Radiation Units and Measurements  (ICRU) and the ICRP to calculate the biological effect of an absorbed dose.


To obtain an effective dose, the calculated absorbed organ dose  D T  is first corrected for the radiation type using factor  W R  to give a weighted average of the equivalent dose quantity  H T  received in irradiated body tissues, and the result is further corrected for the tissues or organs being irradiated using factor  W T , to produce the effective dose quantity  E .


The sum of effective doses to all organs and tissues of the body represents the effective dose for the whole body. If only part of the body is irradiated, then only those regions are used to calculate the effective dose. The tissue weighting factors summate to 1.0, so that if an entire body is radiated with uniformly penetrating external radiation, the effective dose for the entire body is equal to the equivalent dose for the entire body.


The ICRP tissue weighting factors are given in the accompanying table, and the equations used to calculate from either absorbed dose or equivalent dose are also given.


Some tissues like bone marrow are particularly sensitive to radiation, so they are given a weighting factor that is disproportionately large relative to the fraction of body mass they represent. Other tissues like the hard bone surface are particularly insensitive to radiation and are assigned a disproportionally low weighting factor.


Calculating from the equivalent dose:


Calculating from the absorbed dose:


Where


The ICRP tissue weighting factors are chosen to represent the fraction of health risk, or biological effect, which is attributable to the specific tissue named. These weighting factors have been revised twice, as shown in the chart above.


The United States  Nuclear Regulatory Commission  still uses the ICRP's 1977 tissue weighting factors in their regulations, despite the ICRP's later revised recommendations. [ 15 ]


Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in  radiation therapy  for the treatment of cancer and  thyrotoxicosis . Its most common impact is the  induction of cancer  with a  latent period  of years or decades after exposure. High doses can cause visually dramatic  radiation burns , and/or rapid fatality through  acute radiation syndrome . Controlled doses are used for  medical imaging  and  radiotherapy .


The UK  Ionising Radiations Regulations 1999  defines its usage of the term effective dose; "Any reference to an effective dose means the sum of the effective dose to the whole body from external radiation and the committed effective dose from internal radiation." [ 19 ]


The US  Nuclear Regulatory Commission  has retained in the US regulation system the older term  effective dose equivalent  to refer to a similar quantity to the ICRP effective dose. The NRC's  total effective dose equivalent  (TEDE) is the sum of external effective dose with internal committed dose; in other words all sources of dose.


In the US, cumulative equivalent dose due to external whole-body exposure is normally reported to nuclear energy workers in regular dosimetry reports.


The concept of effective dose was introduced in 1975 by Wolfgang Jacobi (1928–2015) in his publication "The concept of an effective dose: a proposal for the combination of organ doses". [ 6 ] [ 20 ]  It was quickly included in 1977 as “effective dose equivalent” into Publication 26 by the ICRP. In 1991, ICRP publication 60 shortened the name to "effective dose." [ 21 ]  This quantity is sometimes incorrectly referred to as the "dose equivalent" because of the earlier name, and that misnomer in turn causes confusion with  equivalent dose . The tissue weighting factors were revised in 1990 and 2007 due to new data.


At the ICRP 3rd International Symposium on the System of Radiological Protection in October 2015, ICRP Task Group 79 reported on the "Use of Effective Dose as a Risk-related Radiological Protection Quantity".


This included a proposal to discontinue use of equivalent dose as a separate protection quantity. This would avoid confusion between equivalent dose, effective dose and dose equivalent, and to use absorbed dose in Gy as a more appropriate quantity for limiting deterministic effects to the eye lens, skin, hands & feet. [ 22 ]


It was also proposed that effective dose could be used as a rough indicator of possible risk from medical examinations. These proposals will need to go through the following stages:


M.A. Boyd.  "The Confusing World of Radiation Dosimetry - 9444"   (PDF) .  US Environmental Protection Agency . Archived from  the original   (PDF)  on 2016-12-21 . Retrieved  2014-05-26 .  –  an account of chronological differences between USA and ICRP dosimetry systems


Electron resonance imaging  ( ERI ) is a  preclinical imaging  method, together with  positron emission tomography  (PET),  computed tomography scan  (CT scan),  magnetic resonance imaging  (MRI), and other techniques. ERI is dedicated to imaging small laboratory animals, and its unique feature is the ability to detect  free radicals . [ 1 ] [ 2 ]  This technique could also be used for other purposes, such as material science, quality of food, etc. [ 3 ]


For  in vivo  imaging purposes, ERI is a minimally invasive method. It requires an intravenous injection of external substances called  spin probes [ 4 ]  (usually nitroxide or triarylmethyl compounds). The main advantage of ERI modality is the ability to map the tissue microenvironment parameters, e.g., oxygen partial pressure (pO2), redox status,  oxidative stress , thiol concentration,  pH , inorganic phosphorus, viscosity, etc. [ 5 ] [ 6 ] [ 7 ] [ 8 ]  ERI is commonly used to research in the areas of  oncology ,  neurodegenerative disorders , and drug development.


ERI is a preclinical application of electron paramagnetic resonance imaging (EPRI). [ 9 ] [ 2 ]  The term "ERI" was introduced to distinguish a commercial device from EPRI devices normally used in the academic domain.


Electron paramagnetic resonance  (EPR) spectroscopy is dedicated to researching substances with unpaired electrons. It was first introduced in 1944, approximately the same time as a similar phenomenon -  nuclear magnetic resonance  (NMR). [ 10 ] [ 11 ]  Owing to hardware and software limitations, EPR was not developing as rapidly as NMR. This led to a huge gap between these two methods. Therefore, to underline a breakthrough in preclinical imaging by presenting EPRI as a complementary method to the present ones, the term "ERI" was introduced. [ 5 ] [ 6 ]


One of the many possible applications of ERI is the ability to measure the absolute value of oxygen. [ 12 ]  The width of the EPR signal from oxygen-sensitive spin probes depends linearly on tissue oxygen concentration. [ 13 ]  Therefore, the information about the oxygen value is collected directly from the examined areas. Oxygen mapping is commonly used to plan and improve the effectiveness of radiotherapy treatments. [ 14 ] [ 15 ]  Trityl spin probes are the most suitable for use in oxygen imaging. [ 16 ] [ 17 ]


The unique property of ERI is the ability to track  reactive oxygen species  (ROS). [ 18 ]  Those particles are versatile and are constantly generated in living organisms. ROS plays a special role in oxidative and reduction mechanisms. In a normal physiological state, the number of ROS is controlled by  antioxidants . Factors that increase the number of ROS (e.g., ionizing radiation, metal ions, etc.) will cause their overproduction. Therefore, this state leads to an imbalance between those particles and is called oxidative stress. [ 19 ] [ 20 ]


ERI allows for dynamic measurements and 3D tracking of the spin probe. [ 6 ]  In this case, the term "dynamics" refers to the fast repetition of the imaging process and the tracking of changes in the signal intensity for each location imaged over time. Due to the method's high temporal resolution and sensitivity, it is possible to distinguish both the inflow and outflow phases of the spin probe, the bio-distribution, and the time to reach a maximum concentration of the spin probe. [ 6 ]


In natural conditions, free radicals are characterised by an extremely short lifespan, so to capture the EPR signal, an external molecule with a stable free radical must be delivered. Usually, it happens when an injection is made into the animal's body. Two main classes of spin probes are used for imaging: nitroxide and triaryl methyl (TAM, trityl) radicals.


Nitroxide radicals are sensitive to oxygen concentration, pH, thiol concentrations, viscosity, and polarity. [ 2 ]  The issue with these spin probes is their fast reduction, which sometimes leads to loss of the EPR signal. Triarylmethyl radicals are characterised by far longer lifespans and increased stability towards reducing and oxidising biological agents. They are perfect for measuring oxygen concentration, pH, thiol concentrations, inorganic phosphate, and redox status.


Although the aforementioned spin probes are the most popular choice, many more can be used in ERI. One of many examples is  melanin  – a polymeric pigment that contains a mixture of eumelanin and pheomelanin. [ 21 ] [ 22 ]  This is the only substance that occurs in natural conditions and allows for the registration of the EPR signal without the need to deliver extraneous spin probes.


The  empty delta sign  is a  radiologic sign  seen on brain imaging which is associated with  cerebral venous sinus thrombosis . It is usually seen on  magnetic resonance imaging  (MRI) or  computed tomography  (CT) scans with contrast. It is seen as  dural wall  enhancement in the absence of intra-sinus enhancement (there is no enhancement in the lumen of the dural sinus). [ 1 ]   This is due to the presence of a  blood clot  in the  dural venous sinuses . The dural venous sinuses drain blood from the  brain  to the  internal jugular veins , which in turn drains blood to the heart. It has been proposed that the empty delta sign occurs in dural venous thromboses due to contrast material filling the dural venous collateral circulation immediately surrounding the dura whilst being unable to fill the intra-dural sinus space due to the presence of a blood clot. [ 2 ]  The  superior sagittal sinus  is most commonly affected, but the radiologic sign may also be seen in the  transverse sinuses . [ 3 ]


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


EOS  is a  medical imaging  system designed to provide frontal and lateral  radiography  images, while limiting the  X-ray   dose absorbed  by the patient in a sitting or standing position. The system relies on the high sensitivity of a detector ( multi-wire chamber ) invented by  Georges Charpak , which earned him the 1992  Nobel prize . This technology not only enhances patient safety but also improves diagnostic accuracy, making EOS particularly valuable in monitoring musculoskeletal conditions and guiding orthopedic treatments.


EOS is commercialized by the French company  EOS imaging  as an  orthopedic  application whose main feature is the 3D visualization of the  vertebral column  and/or lower limbs of the patients. The device develops statistical models by collecting anteroposterior and lateral 2D images of an individuals entire body.  [ 1 ]


EOS focuses on using an approach that centers around precision medicine, or a medical approach that considers a patient's genetics, environmental factors, and health habits in order to create a more personalized treatment or diagnosis for disease.  [ 2 ]


These images can be used to image the electrical activity within the cells of hearts. [ 3 ]  Richard Barr, a Duke University biomedical engineer, created a computer program  that creates a simulation environment to model the electrical activity within cardiac cells. This allows for medical professionals to gain a deeper understanding of the heart's functionality without an incision needing to be made, because activity among these cells is non-linear and unpredictable. By visualizing the behavior of cardiac cells, this program helps improve our understanding of the human heart, which will improve our ability to develop personalized treatment for heart disease.


Another technique, coined by Elizabeth Bucholz, focuses on a four-dimensional imaging technique using pre-existing MRI technology for mice. This technique involves injecting the liposomal agent into the bloodstream, and then the tool captures images of the heart over time. Once the images are collected, a 4D model of the heart is created, allowing the researchers to analyze the heart's performance and other important health factors. [ 4 ]


EOS offers many more advantages over any other medical imaging techniques. For example, the ability to create 3D reconstructions from its data, a lower dose of radiation, and whole body imaging.  [ 5 ]


EOS imaging  is a medical device company based in  Paris, France , that designs, develops, and markets EOSedge and the EOS system, innovative, orthopedic medical imaging systems, associated with several orthopedic solutions along the patient care pathway – from  diagnosis  to post-operative treatments. The EOS platform targets  musculoskeletal disorders  and  orthopedic surgical care  through 2D  X-ray  scans and 3D skeletal models from stereo-radiographic images of patients in a seated or standing position.


The philosophy of EOS imaging surrounds three main principles: reduction of the  radiation  dose emitted by the technology, relevance and manipulability of calculated clinical parameters, and optimization of the patient care workflow. Currently, over 300 EOS systems are installed in medical centers in 51 different countries, including the United States, Japan, Korea, China, and throughout the European Union.


The EOS imaging technology stems from the scientific findings of  Georges Charpak  ( Nobel Prize in Physics , 1992) concerning radiation detection and  particle physics , especially the  multi-wire chamber . [ 1 ]  Since then, physicists, engineers, radiologists, and surgeons have collaborated to transform these findings into a new technology called the EOS system.


EOS imaging began in 1989 as Biospace Med, a medical company founded by Georges Charpak for the development of his detection technology. In 1999, Marie Meynadier became the CEO of Biospace Med; she developed the company's first subsidiary dedicated to imaging solutions for pre-clinical research – the EOS system.


In 2004, hospitals in Paris, France and Brussels, Belgium finished running clinical tests on the EOS prototype, and in 2005, the first fundraising efforts commenced with the company's first venture capital round.


From 2007 to 2011, the company obtained  CE marking  in Europe and  FDA  approval to market the EOS system and the sterEOS 2D/3D workstation in the United States.


The first installations of EOS in European and North American hospitals and clinics occurred from 2008 to 2010. In 2011, the EOS system was being integrated into clinical routines of medical centers in 10 countries, including the United States, Canada, and Australia.


In 2010, Biospace Med changed its name to EOS imaging.


In 2012, EOS imaging entered the  Euronext Paris  stock exchange (name: EOSI) and had its first installation in Asia.


In 2013, EOS acquired the medical company oneFIT Medical (see Acquisition of oneFIT Medical).
In 2014, EOS provided the EOS system in the Vietnam market (Medic - Medic Hoa Hao) through Bluelight.


In 2015, the CFDA certification in China and the NECA designation in Korea were obtained, allowing the company to further expand its market.


In 2016, the company entered into the Latin American market with the signing of its first contract in Brazil.


In 2019, the company launched EOSedge, its new generation imaging system powered by photon-counting technology.


While based in Paris, France, EOS imaging has five other corporate locations in various regions around the world:  Besançon, France ;  St. Paul, Minnesota , US;  Montreal, Quebec , Canada;  Frankfurt, Germany , and in  Singapore .


In 2013, EOS imaging acquired oneFIT Medical (based in Besançon, France), a  medical software  engineering and manufacturing company dedicated to the development of  surgical planning  software for spine, hip, and knee surgeries and patient-specific orthopedic surgical cutting guides. [ 2 ]


EOS imaging platforms—EOSedge and EOS—deliver unique and specific capabilities that are used in conjunction with EOS Advanced Orthopedic Solutions to generate highly accurate 3D representations of patient anatomy and enable a seamless surgical planning experience.


The EOS examination takes place in an upright scanning cabin where the patient can either stand or sit. With a vertically traveling arm supporting two fine X-ray beams perpendicular to one another, the EOS system acquires frontal and lateral, weight-bearing images of the patient in a functional – standing or sitting – position. These biplanar images are then used to create a 3D model of the patient's skeleton.


The ALARA principle (As Low As Reasonably Achievable) represents a movement to “minimize radiation doses and releases of radioactive materials” by minimizing the time of exposure to radiation, increasing the distance between the human body and the radiation source, and using absorber materials to shield the body from  beta particles , X-rays, and  gamma rays . [ 3 ]


EOS imaging aligns itself with this principle, providing reduced exam times and amounts of radiation in comparison with conventional imaging systems. [ 4 ] [ 5 ]  Furthermore, EOS developed a Micro Dose option that further reduced the radiation exposure by 5.5 times compared to a typical low-dose EOS exam protocol, resulting in a nearly negligible radiation dose. [ 6 ]  Additionally, with Flex Dose technology, EOSedge can deliver up to an 80% overall radiation reduction compared to same acquisition without Flex Dose.


Having reduced-radiation options available for patients has become critical in the world of medical imaging as radiation exposure from artificial sources, such as medical imaging, has increased over the last two decades, [ 7 ]  and many patients require multiple examinations throughout the course of their medical treatment.


The sterEOS workstation enables the generation of patient-specific 3D models of the spine and/or lower limbs from weight-bearing low dose or Micro Dose EOS exams. Once the models are created, clinical parameters are automatically calculated and may be exported as a patient report including 2D images and 3D captures. This report is used by physicians for diagnosis, post-operative assessment, and patient follow-up. sterEOS also enables the exportation of 3D anatomical biomarkers for pre-operative planning.


The EOSapps (kneeEOS, hipEOS, and spineEOS) are online, 3D surgical planning solutions based on the weight-bearing EOS images. Frontal and lateral EOS images are uploaded to the EOS Portal, where the EOS 3DServices team prepares the 3D models and dataset and makes the planning case available online. Surgeons can have access to the patient's anatomy information in 3D, with which they can plan and simulate the effect of different implant selections and positions in 3D. spineEOS is used to plan spine surgeries, hipEOS is used for the planning of  total hip arthroplasty , and kneeEOS is geared towards the planning of  total knee arthroplasty .


The  European Day of Radiology  (EDoR) is an annual day of action that will take place for the first time on February 10, 2011. The day is an initiative of the  European Society of Radiology , an organisation that represents the interests of radiology and its practitioners throughout Europe and also hosts the  European Congress of Radiology .


The European Day of  Radiology  will be held for the first time on February 10, 2011, in honour of the anniversary of the death of  Wilhelm Conrad Röntgen , who first discovered  x-rays .
The goal of the EDoR is to celebrate the achievements and benefits of  radiology  from its beginnings up to the present day and to raise public awareness.


National radiological societies from Austria, Belgium, the Czech Republic, Croatia, France, Georgia, Hungary, Ireland, Italy, Lithuania, the Netherlands, Poland, Portugal, Romania, Spain, Sweden, Switzerland, Turkey and the United Kingdom are taking part in this initiative.


In Ireland, the First European Day of Radiology will be celebrated by the Faculty of Radiologists,  Royal college of Surgeons , and in the UK by the  Royal College of Radiologists . [ 1 ]


The  International Day of Radiology  is the successor to the European Day of Radiology which was established in 2011. The first and only European Day of Radiology was held on February 10, 2011, to commemorate the anniversary of  Röntgen's  death.


In  diagnostic radiology , the  F-factor  is the  conversion factor  between  exposure  to  ionizing radiation  and the  absorbed dose  from that radiation. In other words, it converts between the amount of  ionization  in air ( roentgens  or, in  SI units ,  coulombs  per kilogram of absorber material) and the absorbed dose in air ( rads  or  grays ).  The two determinants of the F-factor are the  effective atomic number  (Z) of the material and the type of ionizing radiation being considered.  Since the effective Z of air and  soft tissue  is approximately the same, the F-factor is approximately 1 for many  x-ray imaging  applications.  However,  bone  has an F-factor of up to 4, due to its higher effective Z.


Bushberg et al.,  2002.   The Essential Physics of Medical Imaging.   Philadelphia: Lippincott Williams & Wilkins. (p. 55)


Focal spot blooming  is the unwanted change in the focal spot size of an  X-ray tube  during change in exposure. [ 1 ]


Focal spot blooming is caused due to increased  mAs . When high exposure setting are used, the electron beam from the cathode fail to focus on a particular point because of electrostatic repulsion. [ 2 ]


Forensic radiology  is the discipline which comprises the performance, interpretation and reportage of the  radiological  examinations and procedures which are needed in court procedures or  law enforcement . [ 1 ]  Radiological methods are widely used in  identification ,  age estimation  and establishing  cause of death .
Comparison of ante mortem and post mortem radiographs is one of the means of identification. [ 2 ]  The scanning of baggage, vehicles and individuals have many applications.


Tools like multislice helical computed tomography can be used for detailed documentation of injuries, tissue damage and complications like  air embolism  and  pulmonary aspiration  of blood. These types of digital autopsies offer certain advantages when compared to traditional  autopsies . [ 3 ]


G-arm medical imaging  systems are based on  fluoroscopic X-ray  and are used for a variety of  diagnostic imaging  and minimally invasive  surgical procedures . The name is derived from the G-shaped arm used to connect two  X-ray generators  and two X-ray detectors,  image intensifiers  or digital  flat panel detectors , to one another. The main advantage of the G-arm, compared to a conventional  C-arm system , is that it combines a pair of X-ray chains facilitating simultaneous views in two  perpendicular  planes, also called G-arm imaging.


Fluoroscopic X-ray  is used for a variety of  diagnostic imaging  and minimally invasive  surgical procedures . For surgery it is practical to use a mobile C-arm system where the  x-ray generator  and  x-ray detector  are placed on a C-shaped arm positioned directly opposite from and aligned centrally to each other. The C-arm can be moved horizontally, vertically and around the swivel axes, so that X-ray images of the patient can be produced from different angles. The disadvantage of the C-arm is that imaging is limited to only one plane at a time.


For precision  surgery procedures , for example in  orthopedics , [ 1 ]  it is necessary to generate a view of the surgical site from two  perpendicular  viewing positions, usually a  frontal  and a  lateral  view. With a C-arm system this can only be achieved by manually repositioning the C-arm for the second view. This can be challenging due to the presence of  sterile drapes  and other surgical devices. Bringing the x-ray generator from a  non-sterile area , underneath the  operating table  to a horizontal position close do the patient can compromise the sterility of the surgical area and increase the risks of  infections .
Shifting the C-arm must normally be done many times during the surgical procedure, taking additional time and increasing the  radiation exposure  to patient and staff.
With the G-arm the stand can stay in a fixed position during the entire surgical procedure as both imaging planes can be viewed simultaneously. Benefits are shorter procedures, [ 2 ] [ 3 ]  higher accuracy, [ 4 ] [ 5 ] [ 6 ]  and  lower radiation exposure. [ 7 ] [ 8 ] [ 9 ]  The fixed position of the stand also ensures a better  sterility.


A G-arm medical imaging system is typically composed by the following basic elements:


A .	A movable stand


B .	X-ray source and detector for the frontal view.


C. 	X-ray source and detector for the lateral view


D. 	Patient table with extensions (here shown in position for a hip surgery)


E. 	Control unit with post-processing image software [ 10 ]  and displays for the two perpendicular imaging planes


X-ray detectors, the height of the stand and the angle of the G-Arm may be motorized or manually moved for fine adjustment of the  iso-center  of the x-ray beams.


Due to the benefits resulting from the ability to simultaneously view two perpendicular planes G-arm Medical Imaging systems are mainly used for  orthopedic  and  traumatic surgery  procedures, such as  hips ,  knees  and  spine .


The G-Arm Imaging system is originating from a patented invention [ 11 ]  from 1970 by the Swedish company  Saab AB , an aerospace and automobile manufacturer who at that time also was active within   the field of medical devices.
In the original product the two x-ray chains were placed in an annular stand. The product, called Multiplane, had some practical disadvantages due to the closed form of the stand. Later a part of the annular stand was cut out and the G-arm was born.


The G-Arm concept has been gradually developed to its current form. In 2002 the concept was acquired by the company Scanflex Healthcare AB based in Stockholm, Sweden who has refined the product and is marketing it worldwide under the trademark, Biplanar (trademark registration cancelled 2011). [ 12 ]  The G-Arm concept was also adopted in 2011 by Beijing East Whale Imaging Tech Co., who hold the registered trademarks for G-Arm and MultiScan G-Arm System under this category [ 13 ] [ 14 ]  and a number of related patents. [ 15 ]  The company was founded in 1998 and is based in Beijing, China. Whale Imaging Inc, its R&D and marketing headquarters, is based near Boston, USA. [ 16 ]  The Whale G-Arm received a Spine Technology award in 2014. [ 17 ]


Global radiology , a subspecialty of  diagnostic radiology , [ 1 ]  comprises the study and practice of improving access to radiology resources in poor and developing countries, and addressing global health inequities through the application of radiology. [ 2 ]  Similar to the fields of  public health  and  global health , global radiology draws on and encourages collaboration with nonmedical specialties relevant to disease patterns and the provision of medical services, including  economic development ,  biomedical technology ,  engineering  and  social sciences . [ 2 ]


According to the  World Health Organization , [ 3 ]  one half to two-thirds of the  global population  lacks access to radiological services due primarily to shortages in diagnostic equipment and trained personnel. The practice of global outreach radiology, as well as education and training programs related to global radiology, have been spearheaded by organizations including the  American College of Radiology , [ 4 ]  the  Radiological Society of North America , [ 5 ]  the  American Roentgen Ray Society , [ 6 ]  the  Royal College of Radiologists , [ 7 ]  the  International Union of Interventional Radiologists ,  Imaging the World  and the  World Federation of Pediatric Imaging . Growing interest in  global health  among radiology  resident  physicians [ 8 ]  has spurred some radiology  residency  programs to offer global health training. [ 9 ] [ 10 ] [ 11 ]  In 2014, the  American College of Radiology  proposed a formal “global health imaging curriculum” for residents. [ 12 ]


The academic component of global radiology involves the study of obstacles to obtaining access to imaging services and technology, and research on efforts to improve  global health  through  radiology . This work encompasses both  original research  using data collected through radiology outreach projects in specific locales, [ 13 ]  and broader  epidemiological  assessments informed by imaging data. [ 14 ]  Conferences, such as the world congresses hosted by the  International Society of Radiographers and Radiological Technologists , offer academics and non-academics involved in global radiology an opportunity to “discuss data, experiences, and models pertaining to radiology in the developing world and to evaluate potential opportunities for future collaboration.” [ 15 ]  While much of the research published has appeared in various radiology journals, in 2014 the  Journal of Global Radiology ,  founded by Dr. Sarwat Hussain of  University of Massachusetts Medical School , became the first journal dedicated to global radiology. [ 1 ]


The  gloved finger sign  is a  radiologic sign  observed on  chest radiographs  or  CT scans  that indicates the presence of mucoid impaction in the lungs. Mucoid impaction occurs when  bronchi  become dilated and filled with mucus. This abnormality appears as branching tubular opacities projecting out from the  hila  towards the periphery of the lungs, resembling gloved fingers. [ 1 ]  The gloved finger sign has been observed in the imaging of several conditions, including bronchial atresia,  cystic fibrosis ,  bronchiectasis ,  allergic bronchopulmonary aspergillosis ,  foreign body aspiration , benign tumors, and malignancies. [ 2 ]


GXMO  (also fashioned as  GxMO  or  GxmO [ 1 ] ) is an  acronym  for  G eneral  X -Ray  M achine  O perator license. [ 2 ]  It may also refer to the licensing exam. [ 1 ]  Persons who possess this license may add this acronym after their name to demonstrate their qualification.


The  Hirtz compass  is a medical device previously used to determine the location and aid the removal of  bullets  and  shrapnel  in a patient's body. [ 1 ] [ 2 ]  The device would be used by a  surgeon  who would, with the help of  x-ray photographs , precisely remove the foreign object. [ 2 ]  The device would usually give a location within 1 or 2 millimeters of the foreign object. [ 3 ]  At its peak, the  average  rate of projectile removal when the device was used by local surgeons reached approximately 90%. [ 4 ]  The device was extensively used during  World War I .


The Hirtz compass was invented in 1907 by  E. J. Hirtz , a  French   radiologist  working at a military hospital. [ 1 ]


First, the compass is carefully secured and the penetration needle is brought in contact with the skin. The compass will then give the location of the incision and the depth and direction of the projectile. The compass is then removed and an incision is made in the indicated direction. The surgeons left index finger is put into the wound and the compass is secured in place above the surgeon's left hand. The indicator needle is then pressed into the route prepared by the left index. At the point where the indicator needle ends, the surgeon should be able to feel the bullet which can then be removed. [ 5 ]


The procedure requires a large area of skin to be left uncovered, which is sometimes an inconvenience for the surgeon. The main problem with the device is the fact that the patient's soft body parts can change shape and thus give inaccurate results. When the projectile is to be extracted from muscular tissue, the procedure must be done with completely relaxed muscles, therefore needing complete anesthesia. Otherwise, the contractions would displace the foreign object making removal with the aid of the compass difficult. [ 6 ]


The  history of radiation protection  begins at the turn of the 19th and 20th centuries with the realization that  ionizing radiation  from natural and artificial sources can have harmful effects on living organisms. As a result, the study of radiation damage also became a part of this history.


While  radioactive materials  and X-rays were once handled carelessly, increasing awareness of the dangers of  radiation  in the 20th century led to the implementation of various preventive measures worldwide, resulting in the establishment of radiation protection regulations. Although  radiologists  were the first victims, they also played a crucial role in advancing radiological progress and their sacrifices will always be remembered. Radiation damage caused many people to suffer amputations or die of cancer. The use of radioactive substances in everyday life was once fashionable, but over time, the health effects became known. Investigations into the causes of these effects have led to increased awareness of protective measures. The dropping of  atomic bombs  during  World War II  brought about a drastic change in attitudes towards radiation. The effects of natural  cosmic radiation , radioactive substances such as  radon  and  radium  found in the environment, and the potential health hazards of non-ionizing radiation are well-recognized. Protective measures have been developed and implemented worldwide, monitoring devices have been created, and radiation protection laws and regulations have been enacted.


In the 21st century, regulations are becoming even stricter. The permissible limits for ionizing radiation intensity are consistently being revised downward. The concept of radiation protection now includes regulations for the handling of  non-ionizing  radiation.


In the Federal Republic of Germany, radiation protection regulations are developed and issued by the  Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection  (BMUV). The  Federal Office for Radiation Protection  is involved in the technical work. [ 2 ]  In  Switzerland , the Radiation Protection Division of the  Federal Office of Public Health  is responsible, [ 3 ]  and in  Austria , the  Ministry of Climate Action and Energy . [ 4 ]


The discovery of  X-rays  by  Wilhelm Conrad Röntgen  (1845-1923) in 1895 led to extensive experimentation by scientists, physicians, and inventors. The first X-ray machines produced extremely unfavorable radiation spectra for imaging with extremely high skin doses. [ 5 ]  In February 1896, John Daniel and  William Lofland Dudley  (1859–1914) of  Vanderbilt University  conducted an experiment in which Dudley's head was X-rayed, resulting in hair loss.  Herbert D. Hawks , a graduate of  Columbia University , suffered severe burns on his hands and chest during demonstration experiments with X-rays. [ 6 ] [ 7 ]   Burns  and  hair loss  were reported in scientific journals.  Nikola Tesla  (1856–1943) was one of the first researchers to explicitly warn of the potential dangers of X-rays in the  Electrical Review  on May 5, 1897 - after initially claiming them to be completely harmless. He suffered massive radiation damage after his experiments. [ 8 ]  Nevertheless, some doctors at the time still claimed that X-rays had no effect on humans. [ 9 ]  Until the 1940s, X-ray machines were operated without any protective safeguards. [ 9 ]


Röntgen himself was spared the fate of the other X-ray users by habit. He always carried the unexposed photographic plates in his pockets and found that they were exposed if he remained in the same room during the exposure. So he regularly left the room when he took X-rays. [ citation needed ]


The use of X-rays for diagnostic purposes in  dentistry  was made possible by the pioneering work of  C. Edmund Kells  (1856-1928), a New Orleans dentist who demonstrated them to dentists in Asheville, North Carolina, in July 1896. [ 10 ]  Kells committed suicide after suffering from radiation-induced cancer for many years. He had been amputated one finger at a time, later his entire hand, followed by his forearm and then his entire arm.


Otto Walkhoff  (1860-1934), one of the most important German dentists in history, took X-rays of himself in 1896 and is considered a pioneer in dental radiology. He described the required exposure time of 25 minutes as an "ordeal". Braunschweig's medical community later commissioned him to set up and supervise a central X-ray facility. In 1898, the year radium was discovered, he also tested the  use of radium  in medicine in a self-experiment using an amount of 0.2 grams of  radium bromide . Walkhoff observed that cancerous mice exposed to radium radiation died significantly later than a control group of untreated mice. He thus initiated the development of radiation research for the treatment of  tumors . [ 11 ] [ 12 ]


The Armenian-American radiologist  Mihran Krikor Kassabian  (1870-1910), vice president of the  American Roentgen Ray Society  (ARRS), was concerned about the irritating effects of X-rays. In a publication, he mentioned his increasing problems with his hands. Although Kassabian recognized X-rays as the cause, he avoided making this reference so as not to hinder the progress of radiology. In 1902, he suffered a severe radiation burn on his hand. Six years later, the hand became  necrotic  and two fingers of his left hand were amputated. Kassabian kept a diary and photographed his hands as the tissue damage progressed. He died of cancer in 1910. [ 13 ]


Many of the early X-ray and radioactivity researchers went down in history as "martyrs for science." In her article,  The Miracle and the Martyrs , Sarah Zobel of the  University of Vermont  tells of a 1920 banquet held to honor many of the pioneers of X-rays. Chicken was served for dinner: "Shortly after the meal was served, it could be seen that some of the participants were unable to enjoy the meal. After years of working with X-rays, many of the participants had lost fingers or hands due to radiation exposure and were unable to cut the meat themselves". [ 14 ]  The first American to die from radiation exposure was  Clarence Madison Dally  (1845-1904), an assistant to  Thomas Alva Edison  (1847-1931). Edison began studying X-rays almost immediately after Röntgen's discovery and delegated the task to Dally. Over time, Dally underwent more than 100 skin operations due to radiation damage. Eventually, both of his arms had to be amputated. His death led Edison to abandon all further X-ray research in 1904.


One of the pioneers was the Austrian  Gustav Kaiser  (1871-1954), who in 1896 succeeded in photographing a double toe with an exposure time of 1½-2 hours. Due to the limited knowledge at the time, he also suffered severe radiation damage to his hands, losing several fingers and his right metacarpal. His work was the basis for, among other things, the construction of lead rubber aprons. [ 15 ]   Heinrich Albers-Schönberg  (1865-1921), the world's first professor of radiology, recommended gonadal protection for testicles and ovaries in 1903. He was one of the first to protect germ cells not only from acute radiation damage but also from small doses of radiation that could accumulate over time and cause late damage. Albers-Schönberg died at the age of 56 from radiation damage, [ 16 ]  as did  Guido Holzknecht  and  Elizabeth Fleischman .


Since April 4, 1936, a  radiology memorial  in the garden of the  of Hamburg's St. Georg Hospital has commemorated the 359 victims from 23 countries who were among the first medical users of X-rays. [ 17 ]


In 1896, the engineer Wolfram Fuchs, based on his experience with numerous X-ray examinations, recommended keeping the exposure time as short as possible, staying away from the tube, and covering the skin with  Vaseline . [ 18 ]  In 1897, Chicago doctors William Fuchs and Otto Schmidt became the first users to have to pay compensation to a patient for radiation damage. [ 19 ] [ 20 ]


In 1901, dentist  William Herbert Rollins  (1852-1929) called for using  lead-glass   goggles  when working with X-rays, for the X-ray tube to be encased in lead, and for all areas of the body to be covered with lead aprons. He published over 200 articles on the potential dangers of X-rays, but his suggestions were long ignored. A year later, Rollins wrote in despair that his warnings about the dangers of X-rays were not being heeded by either the industry or his colleagues. By this time, Rollins had demonstrated that X-rays could kill laboratory animals and induce  miscarriages  in guinea pigs. Rollins' achievements were not recognized until later. Since then, he has gone down in the history of radiology as the "father of radiation protection. He became a member of the  Radiological Society of North America  and its first treasurer. [ 21 ]


Radiation protection continued to develop with the invention of new measuring devices such as the  chromoradiometer  by Guido Holzknecht (1872-1931) in 1902, [ 22 ]  the  radiometer  by  Raymond Sabouraud  (1864-1938) and  Henri Noiré  (1878–1937) [ 23 ]  in 1904/05, and the  quantimeter  by  Robert Kienböck  (1873-1951) in 1905, [ 24 ]  which made it possible to determine maximum doses at which there was a high probability that no skin changes would occur.  Radium  was also included by the  British Roentgen Society , which published its first memorandum on radium protection in 1921.


Since the 1920s,  pedoscopes  have been installed in many shoe stores in North America and Europe, more than 10,000 in the U.S. alone, following the invention of Jacob Lowe, a Boston physicist. They were X-ray machines used to check the fit of shoes and to promote sales, especially to children. Children were particularly fascinated by the sight of their footbones. X-rays were often taken several times daily to evaluate the fit of different shoes. Most were available in shoe stores until the early 1970s. The  energy dose absorbed  by the customer was up to 116  rads , or 1.16 grays. In the 1950s, when medical knowledge of the health risks was already available, pedoscopes came with warnings that shoe-buyers should not be scanned more than three times a day and twelve times a year. [ 25 ]