The incidence of  hematogenous  spread of follicular carcinomas is 21–33 % and that of PTCs is 2–14 %. In medullary thyroid cancer and anaplastic thyroid cancer, distant metastasis was reported in 25% and 40% of patients, respectively. Distant metastases from DTCs tend to have a more favourable prognosis. Distant metastatic disease may appear years after the initial presentation. Therefore, imaging for distant metastases is usually done pre-operatively for anaplastic thyroid cancer and post-operatively for DTCs. DTC distant metastases sites include the lung (50%), bone (25%), lung and bone (20%), followed by other sites (5%). [ 1 ]


The thyroid cancer recurrence rate is reported to range from 7% to 14%. Recurrence is usually detected within the first decade after the initial disease diagnosis. Large lymph node metastasis is considered the strongest predictor for thyroid cancer recurrence. Post-treatment surveillance for recurrent disease depends on the cancer type and staging. Patients with DTC are usually treated with total thyroidectomy and RAI ablation. Patients should have baseline neck US evaluation at 6–12 months after the RAI ablation and then periodically, depending on the patient's risk for recurrent disease and  thyroglobulin  (Tg) status. After the first post-operative RAI ablation, further RAI imaging is not necessary if the patient has normal neck US, undetectable Tg level under TSH stimulation, and negative antithyroglobulin (TgAb). Annual neck US with or without FNA, along with measurement of serum Tg and serum TgAb, is usually sufficient for post-treatment surveillance in those patients. Moreover, annual US is appropriate in patients with medullary cancer and normal calcitonin levels. [ 1 ]


The likelihood of positive anatomic imaging is greater when serum Tg is >10 ng/mL. A diagnostic CT scan adds additional value to neck US in detecting central compartment macro-metastases in the mediastinum and retro-tracheal area. According to the recent  American Thyroid Association  guidelines, an upper chest and neck CT scan with IV contrast should be obtained when: 1) neck US is inadequate in visualizing possible local nodal disease (high Tg, negative neck US, and RAI imaging); 2) US is not able to delineate the disease completely, as in the case of bulky recurrent nodal disease; or 3) evaluation of possible recurrent invasive disease is needed (Figs. 7, 88 and and9).9). CT scans are also the most sensitive diagnostic tool for the detection of pulmonary  micro-metastases . Many of the neck US features that are considered as suggestive signs of disease recurrence are also applicable to CT examination. These signs might include sizable rounded nodules in the thyroid bed, fine calcifications, or cystic change. [ 1 ]


In cases of elevated thyroglobulin with negative neck US and iodine whole body  scintigraphy  (WBS),  fluorodeoxyglucose  (FDG)  positron emission tomography  (PET) is the next modality of choice. Dedifferentiated thyroid carcinoma usually has avid FDG-PET uptake and a negative radioiodine scan typically does not respond to RAI therapy and has a poorer prognosis. There is not yet consensus in the research literature on whether cross-sectional imaging (CT or MRI) or an 18FDG-PET/CT scan should be performed as the first-line imaging modality for such patients. Enhanced CT scan was thought to be more sensitive for the detection of lymph node metastases. Nonetheless, scans using modern PET/CT equipment are as reliable as a proper routine staging CT scan. Many lesions can be found on 18FDG-PET/CT scanning despite the lack of IV contrast injection. However, differentiation between local recurrence versus lymph node metastases and detection of direct involvement of the aerodigestive axis or vascular structures are not technically possible in the absence of IV contrast administration. For these reasons, 18FDG-PET/CT utilizing contrast administration should be considered for most patients with extensive disease. [ 1 ]


Metastasis to the thyroid is rare and represents 5.5% of biopsied thyroid malignancies. It is commonly found with cancers originating from the breast, renal cell, lung, melanoma, and colon. Direct invasion from adjacent structures such as the  pharynx ,  larynx ,  trachea , or oesophagus has been reported (Fig. 10). Metastatic disease has a non-specific appearance. [ 1 ]


The presence of ITNs in patients with another known malignancy is a common clinical problem with controversial management guidelines. Wilhelm et al. followed 41 patients with a known extra-thyroid malignancy and ITNs; 35 of them met the criterion for biopsy (nodule ≥ 1 cm). Pathology revealed four papillary thyroid cancers and five micropapillary thyroid cancers. Only two metastatic cancers were detected. Clinical history (history of radiation, age, endocrine syndromes), TSH, nodule size, and sonographic features are important to determine which nodule(s) should be followed or biopsied. However, existing guidelines do not specifically address how to approach ITNs detected on CT scans in such a specific patient population. [ 1 ]


Thyroid lymphoma represents about 5% of thyroid malignancies.  Non-Hodgkin's lymphoma  is the most common type and can be secondary to generalized lymphoma or a primary tumour. Primary  thyroid lymphoma  usually pre-exists with  Hashimoto's thyroiditis . On CT scans with and without contrast, lymphomas tend to have low attenuation values. Thyroid lymphomas have a variable appearance and mostly manifest as a solitary mass (80%). They may also manifest as multiple nodules (15% to 20%) or as a bulky mass replacing the entire gland with extra-thyroid extension (Figs. 11 and and12).12). The presence of cervical lymphadenopathy supports such a diagnosis. Although it is uncommon, tumour necrosis has been reported. [ 1 ]


A goiter is an abnormal thyroid gland proliferation that manifests as multi-nodular, uni-nodular, or non-nodular diffuse glandular enlargement. A goiter is formed of solid matrix, colloid cysts, blood products, calcification, and fibrosis, and this heterogeneity may lead to variable appearances on a CT scan (Figs. 13, 1414 and and15)15). The US is more sensitive in evaluating thyroid nodules within a goiter; however, a symptomatic goiter may require surgical treatment with total thyroidectomy, and in this case CT plays an additional role in preoperative evaluation. Specific aspects for examination on a CT scan during the preoperative evaluation for goiter include extension, mass effect, and suspicious features of malignancy. [ 1 ]


Malignancy can coexist within the goiter and a CT scan may give a clue if there are abnormal cervical lymph nodes and/or signs of invasion. Retrosternal extension (Fig. 15) could affect the surgical approach, as a lower extent may require a partial or total sternotomy to facilitate complete resection. Therefore, the distance of the retrosternal extent from the sternal notch should be measured on a sagittal image. [ 1 ]


The interpreting radiologist should describe the mass effect, detailing its degree and direction of displacement of central structures, including the trachea, oesophagus, larynx, and pharynx. Attention should be directed to the upper extent of the goiter and structures immediately surrounding the thyroid gland, including the neuro-vascular structures, retropharyngeal space, and pre-vertebral space. The reporting radiologist should evaluate the vocal cords for symmetry and signs of vocal cord palsy. [ 1 ]


Inflammatory thyroid disorders include acute infectious thyroiditis,  Hashimoto's thyroiditis ,  Riedel's thyroiditis , and  granulomatous thyroiditis  (de Quervain's). Hashimoto's thyroiditis is associated with an increased risk of  lymphoma  and papillary thyroid carcinoma. The CT scan findings of thyroiditis are nonspecific and variable (Figs. 14, 1515 and and16)16). The thyroid gland has a very high iodine concentration, resulting in high CT attenuation (80–100 Hounsfield Units). The presence of thyroiditis can be suggested by a diffusely enlarged and hypo-attenuating (around 45 Hounsfield Units) thyroid gland. This is probably due to follicular cell destruction and reduced thyroid iodine concentration. Marked homogeneous enhancement is typically expected. Therefore, moderate thyroid enhancement in a case of thyroiditis suggests a diffuse inflammatory process. It is essential to clinically correlate this with a thyroid function test and serum autoantibody levels. [ 1 ]


During embryogenesis, the bi-lobed thyroid migrates inferiorly from the foramen cecum of the tongue to the lower neck. Initially, the thyroid primordium passes anterior to the primordial hyoid bone, before it loops posteriorly and inferiorly to the hyoid bone. Then it continues its descent into the infra-hyoid portion of the neck, anterior to the trachea, thyroid cartilage, and thyroid membrane. Any thyroid residual along the descent course may lead to the development of ectopic thyroid glands. Thyroid carcinomas, thyroiditis, and goiter may develop within any ectopic thyroid tissue. [ 1 ]


Thyroid scanning with technetium-99 m (Tc99m) plays an important role in detecting orthotopic and ectopic thyroid tissue. Both CT scans and US can help detect ectopic tissue when a lesion demonstrates imaging and enhancement characteristics of thyroid tissue. The absence of normally sited thyroid gland in US and CT scans also supports the diagnosis. In addition, US can guide FNA for cytological confirmation of a thyroid lesion. Ectopic thyroid tissue appears as a well-circumscribed, homogeneous, highly attenuating mass relative to adjacent muscles. Normally, it enhances avidly following the administration of iodinated contrast. [ 1 ]


Ectopic thyroid tissue may be detected in the tongue near the foramen cecum (90%) and along the midline between the thyroid isthmus and posterior tongue, lateral neck, mediastinum, and oral cavity. The most frequent location is the base of the tongue (Figs. 16, 1717 and and18).18). In 70% of cases, the ectopic thyroid is the only functional thyroid tissue present in the body (Fig. 18). [ 1 ]


Ectopic thyroid tissue lateral to the orthotopic midline location is rare. The exact anatomical definition of this rare entity is debated in the literature. To avoid confusion, some authors define a lateral neck ectopic thyroid as any thyroid tissue superficial to the strap muscles with no midline continuity. The majority of lateral thyroid ectopia cases have been reported as lesions closely related to the strap muscles. There are few reported cases of ectopic lateral thyroid tissue in the submandibular region, jugulodigastric region, or within the parotid gland substance (Fig. 17). [ 1 ]


The origin of lateral ectopic thyroid tissue is not fully understood. Although this is controversial, some authors suggest that it might have originated from lateral thyroid anlagen ( ultimobranchial bodies ) that failed to fuse with the median anlage during caudal migration. [ 1 ]


A thyroglossal duct cyst (TDC) is a duct remnant between the foramen cecum and thyroid isthmus. Most TDCs are located below the hyoid bone and in the midline. The more caudal the cyst, the more likely it will be off midline within 2 cm (Fig. 19 and and20).20). On a CT scan, a TDC appears as a well-circumscribed area of fluid attenuation with thin walls. The cyst wall can become thick with an enhancing rim indicative of current or previous infection. These cysts maybe complicated by haemorrhage, infection, or malignancy. Therefore, their US and CT scan appearance may vary based on their content. Nodular enhancement within a TDC should initiate further workup to exclude malignancy (Fig. 21). US-guided FNA of these suspicious nodular areas is considered an appropriate next diagnostic step, taking into consideration the high rate of false negative results. [ 1 ]


Parathyroid adenoma  (PA) is the most common cause of  primary hyperparathyroidism . Ectopic parathyroid adenoma is rare. The third and fourth pharyngeal pouches represent the embryological origin of the parathyroid tissues, and ectopic parathyroid adenoma can ultimately develop anywhere along their migration course. In a large retrospective study of patients with primary hyperparathyroidism, PA was detected in the intra-thyroid location in 0.7% of cases. In another retrospective analysis of 202 patients with ectopic PA, the intra-thyroidal location was found in 18% of the cases. Intra-thyroid parathyroid adenomas mimic thyroid nodules in CT scans and may even show uptake on a thyroid iodine scan. Correlation with laboratory workup, including measurement of serum parathyroid hormone and calcium level, is required. In addition, the evaluating radiologist should search for radiological manifestations of hyperparathyroidism, such as  osteopenia ,  bone resorption , and  brown tumours  (Fig. 22). [ 1 ]


In the case of inconclusive Tc99m Sestamibi and neck US imaging, FNA biopsy with FNA-iPTH (intact parathyroid hormone) measurement can provide simultaneous biochemical and cytological evidence. Elevated FNA-iPTH measurement, as compared to serum iPTH, is considered positive and diagnostic of parathyroid adenoma. [ 1 ]


Thyroid disorders are common and tend to have non-specific appearances on CT scans. Commonly encountered findings when evaluating a CT scan of the neck include  thyroid nodules , glandular enlargement, and  calcifications . [ 1 ]


Management of ITNs depends on several factors including nodule size, patient's age, overall health status, and the presence or absence of suspicious features such as lymphadenopathy and/or invasion of adjacent structures. [ 1 ]


A CT scan provides additional important information regarding the local extension of cancer or the presence of a mass effect, and is useful in evaluating recurrent disease. Furthermore, CT examination plays a crucial role in preoperative evaluation and preoperative surgical planning for patients with symptomatic goiter. [ 1 ]


Cone beam computed tomography  (or  CBCT , also referred to as  C-arm CT ,  cone beam  volume CT ,  flat panel CT  or  Digital Volume Tomography  (DVT)) is a  medical imaging technique  consisting of  X-ray computed tomography  where the X-rays are divergent, forming a cone. [ 1 ]


CBCT has become increasingly important in treatment planning and diagnosis in  implant dentistry , ENT, orthopedics, and  interventional radiology  (IR), among other things.  Perhaps because of the increased access to such technology, CBCT scanners are now finding many uses in dentistry, such as in the fields of  oral surgery ,  endodontics  and  orthodontics . Integrated CBCT is also an important tool for patient positioning and verification in  image-guided radiation therapy  (IGRT).


During dental/orthodontic imaging, the CBCT scanner rotates around the patient's head, obtaining up to nearly 600 distinct images.  For interventional radiology, the patient is positioned offset to the table so that the region of interest is centered in the field of view for the cone beam.  A single 200 degree rotation over the region of interest acquires a volumetric data set.  The scanning software collects the data and reconstructs it, producing what is termed a  digital volume  composed of three-dimensional  voxels  of anatomical data that can then be manipulated and visualized with specialized software. [ 2 ] [ 3 ]  CBCT shares many similarities with  traditional (fan beam) CT  however there are important differences, particularly for  reconstruction . CBCT has been described as the gold standard for imaging the oral and maxillofacial area.


In the late 1990s, Dr Yoshinori Arai in Japan and Dr Piero Mozzo in Italy independently developed Cone Beam Computed Technology for  oral and maxillofacial radiology . [ 4 ]  The first commercial system (the NewTom 9000) was introduced in the European market in 1996 and into the US market in 2001, by Italian company Quantitative Radiology. [ 2 ] [ 5 ]


Cone beam CT using kilovoltage  X-rays  (as used for  diagnostic , rather than  therapeutic  purposes) attached to a  linear accelerator  treatment machine was first developed in the late 1990s and early 2000s. [ 7 ]  Such systems have since become common on latest generation linacs. [ 8 ]  In the late 2010s CBCT also started to become available on-board  particle therapy  delivery systems. [ 9 ]


While CBCT with  X-ray image intensifiers  was experimented with in the late 1990s, it was not until the adoption of  flat-panel X-ray detectors , with improved contrast and spatial resolution, that CBCT became practical for clinical use in interventional radiology procedures. [ 10 ] [ 11 ]  Many fixed, and even mobile, C-arm fluoroscopy systems are now capable of CBCT acquisitions, in addition to traditional planar fluoroscopy. [ 12 ] [ 13 ]  CBCT aids image guidance during interventional radiology procedures treating various medical conditions including knee osteoarthritis, benign prostatic hyperplasia, and hepatocellular carcinoma. [ 14 ] [ 15 ] [ 16 ] [ 17 ]


The most significant advantage of the CBCT in Endodontics is that it can show critical root canal anatomical features that conventional intraoral or panoramic images cannot. [ 18 ]


According to the American Association of Endodontics, there are numerous specific situations in which 3D images produced by CBCT enhance diagnosis and influence treatment, and its use cannot be disputed over conventional intraoral radiology based on ALARA principles. [ 19 ]


A dental cone beam scan offers useful information when it comes to the assessment and planning of surgical implants. The American Academy of Oral and Maxillofacial Radiology (AAOMR) suggests cone-beam CT as the preferred method for presurgical assessment of dental implant sites. [ 20 ]


As a  3D  rendition, CBCT offers an undistorted view of the  dentition  that can be used to accurately visualize both  erupted  and non-erupted teeth, tooth root orientation and anomalous structures, that conventional  2D radiography  cannot. [ 21 ]


Processing example using x-ray data from a tooth model:


The CBCT scanner offers undistorted views of the extremities. One advantage of orthopedic CBCT is the ability to take weight bearing images of the  lower extremities . In the realm of the  foot  and  ankle  particularly, weight bearing CBCT is gaining momentum due to its ability to combine 3 dimensional and weight bearing information which are of the utmost importance in diagnosis and surgical planning. [ 22 ]  The preferred term used for CBCT in the lower limb is thus WBCT for Weight Bearing CT following the first scientific publications on the subject. [ 23 ] [ 24 ] [ 25 ] [ 26 ]


Image-guided radiation therapy  is a form of  external beam radiotherapy  where the patient is positioned with the organs to be treated accurately matched in position to the treatment field, to reduce the dose to nearby organs which are not being treated. Many organs inside the body move by millimeters relative to the external skin surfaces, and a CBCT scanner mounted on the head of the radiotherapy unit is used immediately before treatment (and sometimes again during treatment) to ensure the patient's organs are in exactly the right position to match the treatment field, and to adjust the position of the treatment table if necessary. The images may also be used to check for other requirements of some types of treatment, such as full or empty bladder, empty rectum, etc. [ 8 ] [ 27 ]  The same cone beam beam source and detector can alternatively be used to take simple X-ray positioning images if the organ shows particularly well on X-ray or if  Fiducial markers  have been inserted into the organ. [ 28 ]


The CBCT scanner is mounted on a C-arm  fluoroscopy  unit in the  interventional radiology  (IR) suite, which offers real time imaging with a stationary patient. This eliminates the time needed to transfer a patient from the  angiography  suite to a conventional  computed tomography  scanner and facilitates a broad spectrum of applications of CBCT during IR procedures. The clinical applications of CBCT in IR include treatment planning, device or implant positioning and assessment, intra-procedural localization, and assessment of procedure endpoints. CBCT is useful as a primary and supplemental form of imaging. It is an excellent adjunct to  DSA  and  fluoroscopy  for  soft tissue  and  vascular  visibility during complex procedures. The use of CBCT before fluoroscopy potentially reduces patient radiation exposure. [ 3 ]


Cone beam CT is used for material analysis,  metrology , and  nondestructive testing  in the manufacturing sector. Cone beam CT is also inspect and detect defects of tiny sizes, such as internal pitting corrosion or cracks of an object in  quality control . [ 34 ]


Cone beam reconstruction algorithms are similar to typical  tomographic reconstruction  algorithms, and methods such as  filtered backprojection  or  iterative reconstruction  may be used. However, since the reconstruction is three-dimensional, modifications such as the FDK algorithm [ 35 ]  may be needed.


Total radiation doses from 3D dental CBCT exams are 96% lower than conventional CT exams, but deliver 5-16x more radiation than standard dental 2D x-ray (OPG). The time of exposure in CBCT is also comparatively less when compared to conventional CT.
 [ 36 ] [ 37 ] [ 38 ] [ 39 ] [ 40 ]


CBCT use is only lightly regulated in the US. The recommended standard of care is to use the smallest possible field of view (FOV), the smallest  voxel  size, the lowest mA setting and the shortest exposure time in conjunction with a pulsed exposure mode of acquisition. [ 41 ]  International organisations such as the  World Health Organization  and  ICRP , as well as many local bodies and legislation, encourage the idea of justification for all medical exposures, where risks and benefits must be weighed up before a procedure goes ahead. [ 42 ]


There are a number of drawbacks of CBCT technology over that of CT scans, such as increased susceptibility to movement artifacts (in first generation machines) and to the lack of appropriate bone density determination. [ 43 ]


The  Hounsfield scale  is used to measure  radiodensity  and, in reference to  CT scans , can provide an accurate absolute density for the type of  tissue  depicted.  The radiodensity, measured in Hounsfield Units (HU, also known as CT number) is inaccurate in CBCT scans because different areas in the scan appear with different  greyscale  values depending on their relative positions in the organ being scanned, despite possessing identical densities, because the image value of a  voxel  of an organ depends on the position [ clarification needed ]  in the image volume. [ 44 ]   HU measured from the same anatomical area with both CBCT and medical-grade CT scanners are not identical [ 45 ]  and are thus unreliable for determination of site-specific, radiographically-identified bone density for purposes such as the placement of dental implants, as there is "no good data to relate the CBCT HU values to bone quality." [ 46 ]


Although some authors have supported the use of CBCT technology to evaluate bone density by measuring HU, [ 47 ] [ 48 ]  such support is provided erroneously because scanned regions of the same density in the skull can have a different grayscale value in the reconstructed CBCT dataset. [ 49 ]


X-ray attenuation of CBCT acquisition systems currently produces different HU values for similar bony and soft tissue structures in different areas of the scanned volume (e.g. dense bone has a specific image value at the level of the menton, but the same bone has a significantly different image value at the level of the cranial base). [ 43 ]


Dental CBCT systems do not employ a standardized system for scaling the grey levels that represent the reconstructed density values and, as such, they are arbitrary and do not allow for assessment of bone quality. [ 50 ]   In the absence of such a standardization, it is difficult to interpret the grey levels or impossible to compare the values resulting from different machines.  While there is a general acknowledgment that this deficiency exists with CBCT systems (in that they do not correctly display HU), there has been little research conducted to attempt to correct this deficiency. [ 51 ]


With time, further advancements in CBCT reconstruction algorithms will allow for improved area detectors, [ 52 ]  and this, together with enhanced postprocessing, will likely solve or reduce this problem. [ 44 ]   A method for establishing attenuation coefficients with which actual HU values can be derived from CBCT "HU" values was published in 2010 and further research is currently underway to perfect this method  in vivo . [ 51 ]


While the practicality of CBCT fosters its increasing application in IR, technical limitations hinder its integration into the field. The two most significant factors that affect successful integration are image quality and time (for set up, image acquisition, and image reconstruction). Compared to  multidetector computed tomography  (MDCT), the wider collimation in CBCT leads to increased scatter radiation and degradation of image quality as demonstrated by artifacts and decreased  contrast-to-noise ratio . The temporal resolution of  cesium iodide  detectors in CBCT slows data acquisition time to approximately 5 to 20 seconds, which increases  motion artifacts . The time required for image reconstruction takes longer for CBCT (1 minute) compared to MDCT (real time) due to the computationally demanding cone beam reconstruction algorithms. [ 3 ] [ 29 ]


Cone-beam spiral computed tomography (CT)  is a  medical imaging  technology that has impacted healthcare since its development in the early 1990s. [ 1 ] [ 2 ]  This technology offers advancements over traditional fan-beam CT, including faster scanning speed, higher image quality, and the ability to generate true three-dimensional volumes, even with contrast-enhancement. It is estimated that the majority of the approximately 300 million CT scans performed annually worldwide use spiral  cone-beam technology.


The concept of cone-beam spiral CT was first proposed by Ge Wang in 1991, [ 3 ]  who also introduced algorithms for approximate image reconstruction. A number of researchers and companies have contributed to the development of this technology. [ 4 ]


In 2002, Alexander Katsevich formulated the first theoretically exact cone-beam spiral CT algorithm. [ 5 ] [ 6 ]  The work on cone-beam spiral CT has become a foundational aspect of modern medical imaging, allowing for accurate volumetric image reconstruction from truncated x-ray cone-beam projections. [ 7 ]


Cone-beam spiral CT uses an X-ray source and multiple detector rows that rotate spirally around the patient. The cone-shaped X-ray beam captures a large volume of data in a single pass, enabling the reconstruction of high-resolution volumetric and dynamic images. Key steps in the cone-beam spiral CT scanning process include:


Cone-beam spiral CT is employed in various medical imaging tasks, including:


Coronary CT angiography  (CTA or CCTA) is the use of  computed tomography (CT) angiography  to assess the  coronary arteries  of the  heart . The patient receives an  intravenous injection  of  radiocontrast  and then the heart is scanned using a high speed  CT scanner , allowing physicians to assess the extent of occlusion in the  coronary arteries , usually in order to diagnose  coronary artery disease .


CTA is superior to  coronary CT calcium scan  in determining the risk of Major Adverse Cardiac Events (MACE). [ 1 ]


Faster CT machines, due to multidetector capabilities, have made imaging of the  heart  and  circulatory system  very practical in a number of clinical settings. [ 2 ]  The faster capability has allowed the imaging of the heart with minimal involuntary motion, which creates  motion blur  on the image, and has a number of practical applications. [ 2 ]  It may be useful in the diagnosis of suspected coronary heart disease, for follow-up of a  coronary artery bypass , for the evaluation of valvular heart disease and for the evaluation of cardiac masses. [ citation needed ]


It is uncertain whether this modality will replace invasive  coronary catheterization . At present, it appears that the greatest utility of cardiac CT lies in ruling out coronary artery disease rather than ruling it in. This is because the test is highly sensitive (over 90% detection rate), so a negative test result largely rules out  coronary artery disease  (i.e. the test has a high  negative predictive value ). [ 3 ]  The test is somewhat less specific, however, so a positive result is less conclusive and may need to be confirmed by subsequent  invasive angiography .


The  positive predictive value  of cardiac CTA is approximately 82% and the  negative predictive value  is around 93%. This means for every 100 patients who appear to have coronary artery disease after CT angiography, 18 of them actually won't have it, and that for every 100 patients who have a negative CT angio test result (i.e. the test says they do not have coronary artery disease), 7 will actually have the disease as defined by the reference standard of invasive coronary angiography via cardiac catheterization. [ 4 ]  Both coronary CT angiography and invasive angiography via cardiac catheterization yield similar diagnostic accuracy when both are being compared to a third reference standard such as  intravascular ultrasound  or  fractional flow reserve . [ 5 ] [ 6 ]


In addition to the diagnostic abilities, cardiac CTA beholds important prognostic information. Stenosis severity and extent of coronary artery disease are important prognostic indicators. [ 7 ]  However, one of the unique features of cardiac CTA is the fact that it enables the visualization of the vessel wall, in a non-invasive manner. Therefore, the technique is able to identify characteristics of coronary artery disease that are associated to the development of  acute coronary syndrome . [ 8 ] [ 9 ]


Because the heart is effectively imaged more than once (described above), cardiac CT angiography can result in a relatively high radiation exposure (around 12  millisievert ), although newer acquisition protocols, have recently been developed which drastically reduce this exposure to around 1 mSv (cfr. Pavone, Fioranelli,  Dowe: Computed Tomography or  Coronary Arteries, Springer 2009). By comparison, a chest X-ray carries a dose of approximately 0.02-0.2 mSv [ 10 ]  and natural  background radiation exposure  is around 2.3 mSv/year. [ 11 ]  Thus, each cardiac CT scan carried out with current protocols (dose approximately 1 mSv) is equivalent to approximately 5-50 chest X-rays or less than 1 year of background radiation. Methods are available to decrease this exposure, however, such as prospectively decreasing radiation output based on the concurrently acquired ECG (i.e. tube current modulation.)  This can result in a significant decrease in radiation exposure, at the risk of compromising image quality if there is any arrhythmia during the acquisition. [ citation needed ]


The significance of the low radiation doses used in diagnostic imaging is unknown, although the possibility of increasing cancer incidence across a population is of significant concern. This potential risk must be weighed against the competing risk of not diagnosing a significant health problem in a particular individual, such as coronary artery disease.


Pregnancy is considered a relative contraindication, similarly to many forms of  medical imaging in pregnancy . The potential harms to a fetus include the application of X-rays in addition to  radiocontrast . Since an iodine-containing  contrast agent  is used, severe contrast agent allergy, uncontrolled hyperthyroidism or renal function impairment are also relative contraindications.  Cardiac arrhythmias ,  coronary artery stents  and  tachycardia  may result in a reduced image quality.


With the advent of subsecond rotation combined with multi-slice CT (up to 320 slices), high resolution and high speed can be obtained at the same time, allowing excellent imaging of the coronary arteries (cardiac CT angiography). Images with even higher temporal resolution can be obtained using multi-cycle (also called multi-segmental) image reconstruction. [ 12 ]


In this technique, a portion of the heart is imaged during one heart cycle while an ECG trace is recorded. During the next heart cycle, the next portion of the heart is scanned for up to 5 total cycles until the entire heart is imaged. The reconstruction algorithm then combines the images from these different cycles to generate one complete image. The advantage of this method is that each image segment is acquired in less time as compared to acquiring the entire heart in one heart cycle, thus improving temporal resolution. The disadvantages are 1) the potential for image artifacts from fusing the image segments and 2) the requirement of additional X-ray radiation for image acquisition.


Dual Source CT  scanners, introduced in 2005, allow higher  temporal resolution  by acquiring a full CT slice in only half a rotation, thus reducing motion blurring at high heart rates and potentially allowing for shorter breath-hold time. This is particularly useful for ill patients having difficulty holding their breath or unable to take heart-rate lowering medication.


The speed advantages of 64-slice MSCT have rapidly established it as the minimum standard for newly installed CT scanners intended for cardiac scanning. Manufacturers have developed 320-slice and true 'volumetric' scanners, primarily for their improved cardiac scanning performance.


Introduction of a CT scanner with a 160 mm detector in 2014 allows for imaging of the whole heart in a single beat without motion of the coronary arteries, regardless of patient heart rate.


The latest MSCT scanners acquire images only at 70-80% of the R-R interval (late diastole). This prospective gating can reduce effective dose from 10 to 15 mSv to as little as 1.2 mSv in follow-up patients acquiring at 75% of the R-R interval. Effective dose using MSCT coronary imaging can average less than the dose in conventional coronary angiography.


A  CT pulmonary angiogram  ( CTPA ) is a medical diagnostic test that employs  computed tomography (CT) angiography  to obtain an image of the  pulmonary arteries . Its main use is to diagnose  pulmonary embolism  (PE). [ 1 ]  It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is an intravenous line.


Modern MDCT (multi-detector CT) scanners are able to deliver images of sufficient resolution within a short time period, such that CTPA has now supplanted previous methods of testing, such as direct  pulmonary angiography , as the  gold standard  for diagnosis of pulmonary embolism. [ 2 ]


The patient receives an  intravenous  injection of an iodine-containing  contrast agent  at a high rate using an injector pump. Images are acquired with the maximum intensity of radio-opaque contrast in the pulmonary arteries. This can be done using  bolus tracking .


A normal CTPA scan will show the contrast filling the pulmonary vessels, appearing as bright white. Any mass filling defects, such as an embolus, will appear dark in place of the contrast, filling/blocking the space where blood should be flowing into the lungs.


CTPA was introduced in the 1990s as an alternative to  ventilation/perfusion scanning  (V/Q scan), which relies on  radionuclide  imaging of the blood vessels of the lung. It is regarded as a highly sensitive and specific test for pulmonary embolism. [ 1 ]


CTPA is typically only requested if pulmonary embolism is suspected clinically. If the probability of PE is considered low, a blood test called  D-dimer  may be requested. If this is negative and risk of a PE is considered negligible, then CTPA or other scans are generally not performed. Most patients will have undergone a  chest X-ray  before CTPA is requested. [ 1 ]


After initial concern that CTPA would miss smaller emboli, a 2007 study comparing CTPA directly with V/Q scanning found that CTPA identified more emboli without increasing the risk of long-term complications compared to V/Q scanning. [ 3 ]  A V/Q scan may still be recommended when a lower  radiation dose  is required. [ 4 ]


On CTPA, acute emboli have been found at  radiodensities  ranging between about 5 and 65  Hounsfield units  (HU), while chronic emboli have ranged between about 30 and 150. [ 5 ]


CTPA is less desirable in  pregnancy  due to the amount of ionizing radiation required, which may damage the breasts, which are particularly sensitive during pregnancy, and because of concerns of the effects of iodine on the fetus'  thyroid  gland. [ 6 ]  V/Q scans can offer lower radiation doses, and may be adapted to further reduce the dose by omitting the lung ventilation portion of the exam. They are therefore recommended to be preferentially applied to pregnant patients. [ 7 ] [ 8 ]  Diagnostic algorithms for pulmonary embolism in pregnancy vary; however, a common compromise is to perform ultrasound testing for  deep vein thrombosis  of the legs, and if this is positive, make the diagnosis of pulmonary embolism on the basis of symptoms and presence of the DVT. CTPA would then only be performed if exhaustive non-radiation based testing could not make a positive diagnosis.


CTPA is contraindicated in known or suspected  allergy  to  contrast media  or in  kidney failure  (where contrast agents could worsen the kidney function). [ 3 ]


The best results are obtained using  multidetector computed tomography  (MDCT) scanners. [ 9 ]


An  intravenous cannula  is required for the administration of  iodinated contrast . The typical dose is 30-40 g of iodine (corresponding to 20–30 cc of 370 mg/ml iodine solution). [ 10 ]  However, for patients at high risk of  contrast-induced nephropathy , it is possible to reduce the required amount of contrast using  dual energy CT . With such a protocol, only 7–10 g of iodine (20–30 cc of 370 mg/ml iodine solution) may be needed. [ 10 ]  Many hospitals use  bolus tracking , where the scan commences when the contrast is detected at the level of the proximal  pulmonary arteries . If this is done manually, scanning commences about 10–12 seconds after the injection has started. Slices of 1–3 mm. are performed at 1–3 mm. intervals, depending on the nature of the scanner (single- versus multidetector). [ 3 ]


High contrast flow rate of 4ml/sec through 18G branula at  antecubital fossa  is recommended to achieve optimal quality images. However, for those with  peripheral arterial disease  and those with  central venous catheter  with low flow rate, 2.0 to 2.5 ml/sec are still manage to produce acceptable images. [ 11 ]


State of the art  modern CT scanners with a scan rate of up to 320 mm/s can acquire all the images within a 1-second X-ray exposure, avoiding the problems of respiratory motion, cardiac motion and contrast draining from the pulmonary circulation during the study. Even though the actual scan may be completed in 1 second or less, considerable staff and patient time is required for preparation of the contrast agent, positioning on the scanner and planning the scan. This is particularly the case, as patients undergoing CTPA are frequently seriously unwell requiring  oxygen  treatment and/or close monitoring.


On CTPA, the pulmonary vessels are filled with contrast, and appear white. Any mass filling defects ( embolus  or other matter such as  fat ) appears darker. Ideally, the scan should be complete before the contrast reaches the left side of the heart and the  aorta , as this may mean contrast has drained from the pulmonary arteries, or require a larger dose of contrast media. [ 12 ]


Other from assessing any filing defect within the pulmonary trunk and its segmental branches, the diameter of the right heart can be compared with diameter of the left heart. The right heart diameter should not be more than the diameter of left heart. Normally, the interventricular septum should mildly bulge into the right ventricle due to high pressure within the left ventricle. Any reverse bulge or flattening of the interventricular septum indicates  pulmonary hypertension . [ 12 ]


Pericardial effusion  may also be seen in pulmonary hypertension. Thickening of pericardium more than 4 mm or pericardial calcification indicates  constrictive pericarditis . [ 12 ]


Digital radiography  is a form of  radiography  that uses x-ray–sensitive plates to directly capture data during the patient examination, immediately transferring it to a computer system without the use of an intermediate cassette. [ 1 ]  Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also, less  radiation  can be used to produce an image of similar  contrast  to conventional radiography.


Instead of X-ray film, digital radiography uses a digital image capture device. This gives advantages of immediate image preview and availability; elimination of costly film processing steps; a wider dynamic range, which makes it more forgiving for over- and under-exposure; as well as the ability to apply special image processing techniques that enhance overall display quality of the image.


Flat panel detectors (FPDs) are the most common kind of direct digital detectors. [ 2 ]  They are classified in two main categories:


1.  Indirect FPDs   Amorphous silicon  (a-Si) is the most common material of commercial FPDs. Combining a-Si detectors with a  scintillator  in the detector’s outer layer, which is made from  caesium iodide  (CsI) or  gadolinium oxysulfide  (Gd 2 O 2 S), converts X-rays to light. Because of this conversion the a-Si detector is considered an indirect imaging device. The light is channeled through the a-Si photodiode layer where it is converted to a digital output signal. The digital signal is then read out by  thin film transistors  (TFTs) or fiber-coupled CCDs. [ 3 ]


2.  Direct FPDs . Amorphous  selenium  (a-Se) FPDs are known as “direct” detectors because X-ray  photons  are converted directly into charge. The outer layer of the flat panel in this design is typically a high-voltage  bias electrode . X-ray photons create  electron-hole pairs  in a-Se, and the transit of these electrons and holes depends on the potential of the bias voltage charge. As the holes are replaced with electrons, the resultant charge pattern in the selenium layer is read out by a TFT array, active matrix array, electrometer probes or microplasma line addressing. [ 3 ] [ 4 ]


Detectors based on  CMOS  and  charge-coupled device  (CCD) have also been developed, but despite lower costs compared to FPDs of some systems, bulky designs and worse image quality have precluded widespread adoption. [ 5 ]


A high-density line-scan solid state detector is composed of a photostimulable barium fluorobromide doped with europium (BaFBr:Eu) or caesium bromide (CsBr) phosphor. The phosphor detector records the X-ray energy during exposure and is scanned by a laser diode to excite the stored energy which is released and read out by a digital image capture array of a CCD.


Phosphor plate radiography [ 6 ]  resembles the old analogue system of a light sensitive film sandwiched between two x-ray sensitive screens, the difference being the analogue film has been replaced by an imaging plate with photostimulable phosphor (PSP), which records the image to be read by an image reading device, which transfers the image usually to a  Picture archiving and communication system  (PACS). [ 6 ]  It is also called photostimulable phosphor (PSP) plate-based radiography or  computed radiography [ 7 ]  (not to be confused with  computed tomography  which uses computer processing to convert multiple projectional radiographies to a  3D image ).


After X-ray exposure the plate (sheet) is placed in a special scanner where the  latent image  is retrieved point by point and digitized, using  laser  light scanning. The digitized images are stored and displayed on the computer screen. [ 7 ]  Phosphor plate radiography has been described as having an advantage of fitting within any pre-existing equipment without modification because it replaces the existing film; however, it includes extra costs for the scanner and replacement of scratched plates.


Initially phosphor plate radiography was the system of choice; early DR [ clarification needed ]  systems were prohibitively expensive (each cassette costs £40-£50K), and as the 'technology was being taken to the patient', prone to damage. [ 8 ]  Since there is no physical printout, and after the readout process a digital image is obtained, CR [ clarification needed ]  has been known [ by whom? ]  as an indirect digital technology, bridging the gap between x-ray film and fully digital detectors. [ 9 ] [ 10 ]


Digital radiography (DR) has existed in various forms (for example, CCD and amorphous Silicon imagers) in the security X-ray inspection field for over 20 years and is steadily replacing the use of film for inspection X-rays in the Security and  nondestructive testing  (NDT) fields. [ 11 ]  DR has opened a window of opportunity for the security NDT industry due to several key advantages including excellent image quality, high POD (probability of detection), portability, environmental friendliness and immediate imaging. [ 12 ]


Nondestructive testing of materials is vital in fields such as  aerospace  and  electronics  where integrity of materials is vital for safety and cost reasons. [ 13 ]  Advantages of digital technologies include the ability to provide results in real time. [ 14 ]


In  radiography ,  focal plane tomography [ 1 ]  is  tomography  (imaging a single plane, or slice, of an object) by simultaneously moving the  X-ray generator  and  X-ray detector  so as to keep a consistent exposure of only the plane of interest during image acquisition. This was the main method of obtaining tomographs in  medical imaging  until the late-1970s. It has since been largely replaced by more advanced imaging techniques such as  CT  and  MRI . It remains in use today in a few specialized applications, such as for acquiring  orthopantomographs  of the jaw in  dental radiography .


Focal plane tomography’s development began in the 1930s as a means of reducing the problem of  superimposition  of structures which is inherent to  projectional radiography . [ 2 ]  It was invented in parallel by, among others, by the French physician  Bocage , the Italian radiologist  Alessandro Vallebona  and the Dutch radiologist  Bernard George Ziedses des Plantes . [ 3 ]


Focal plane tomography generally uses mechanical movement of an  X-ray  source and film in unison to generate a tomogram using the principles of  projective geometry . [ 4 ]  Synchronizing the movement of the radiation source and detector which are situated in the opposite direction from each other causes structures which are not in the  focal plane  being studied to blur out.


The blurring provided by focal plane tomography is only marginally effective, since it only occurs in the  X   plane . Moreover, since focal plane tomography uses plain X-rays, it is not particularly effective at resolving soft tissues.


The increased availability and power of computers in the 1960s and 70s gave rise to new imaging techniques such as CT and MRI which use computational (in addition to or in lieu of mechanical) methods to acquire and process tomographic image data, and which do not suffer from the limitations of focal plane tomography.


Initially focal plane tomography used simple linear movements. The technique advanced through the mid-twentieth century however, steadily producing sharper images, and with a greater ability to vary the thickness of the cross-section being examined. [ 4 ]  This was achieved through the introduction of more complex, pluridirectional devices that can move in more than one plane and perform more effective blurring.


This is the most basic form of conventional tomography. The  X-ray tube  moved from point "A" to point "B" above the patient, while the detector (such as cassette holder or "bucky") moves simultaneously under the patient from point "B" to point "A". [ 5 ]  The  fulcrum , or pivot point, is set to the area of interest. In this manner, the points above and below the focal plane are blurred out, just as the background is blurred when panning a camera during exposure. Rarely used, and has largely been replaced by  computed tomography  (CT).


This was achieved using a more advanced X-ray apparatus that allows for more sophisticated and continuous movements of the X-ray tube and film. With this technique, a number of complex synchronous geometrical movements could be programmed, such as hypocycloidic, circular, figure 8, and  elliptical .  Philips  Medical Systems for example produced one such device called the 'Polytome'. [ 4 ]  This pluridirectional unit was still in use into the 1990s, as its resulting images for small or difficult physiology, such as the inner ear, were still difficult to image with CTs at that time. As the resolution of CT scanners got better, this procedure was taken over by CT. [ 6 ]


This is a variant of linear tomography, where a limited arc of movement is used, resulting in less blurring than linear tomography. [ 7 ]  It is still used in some centres for visualising the  kidney  during an  intravenous urogram  (IVU), [ 8 ]  though it too is being supplanted by CT. [ 9 ] [ 10 ]


Panoramic radiography  is the only common tomographic examination still in use. This makes use of a complex movement to allow the radiographic examination of the  mandible , as if it were a flat bone. [ 11 ]  It is commonly performed in dental practices and is often referred to as a "Panorex", though this is a trademark of a specific company and not a generic term.


A  full-body scan  is a scan of the patient's entire body as part of the  diagnosis  or treatment of illnesses. If  computed tomography  ( CAT ) scan technology is used, it is known as a  full-body CT scan , though many medical imaging technologies can perform full-body scans.


Full-body CT scans allow a transparent view of the body. For  polytrauma  patients, aggressive use of full-body CT scanning improves early diagnosis of injury and improves survival rates,
 [ 1 ]
with widespread adoption of the technique seen worldwide. [ 2 ]
Full-body CT scans are not indicated in patients with minor or single system trauma, and should be avoided in such patients. [ 1 ]


Many possible malignancies are discovered with a full-body scan, but these are almost always benign. [ 3 ] [ 4 ]  These may not be related to any disease, and may be benign growths,  scar tissue , or the remnants of previous  infections . CT scanning for other reasons sometimes identifies these " incidentalomas ".


However, the significance of radiation exposure as well as costs associated with these studies must be considered, especially in patients with low energy mechanisms of injury and absent physical examination findings consistent with major trauma.


A full-body scan has the potential to identify disease (e.g.  cancer ) in early stages, and early identification can improve the success of curative efforts.  Controversy arises from the use of full-body scans in the  screening  of patients who have no signs or  symptoms  suggestive of a disease. [ 5 ]  As with any test that screens for disease, the risks of full-body CT scans need to be weighed against the benefit of identifying a treatable disease at an early stage. [ 6 ]


An alternative to a full-body CT scan may be  Magnetic resonance imaging  (MRI) scans. MRI scans are generally more expensive than CT but do not expose the patient to ionizing radiation and are being evaluated for their potential value in screening. [ 7 ]


Compared to most other diagnostic imaging procedures, CT scans result in relatively high  radiation exposure . This exposure may be associated with a very small increase in cancer risk. The question is whether that risk is outweighed by the benefits of diagnosis and therapy [ 8 ]


The procedure has a low rate of finding disease. [ 3 ] [ 4 ]  It can cause confusion regarding  incidentalomas . It is uncertain how to treat some of them, or if treatment is even necessary. [ 9 ]
The test also cannot detect colors, unlike for example a  colonoscopy .


At a cost of  US$ 600 to $3000, full-body scans are expensive, and are rarely covered by insurance. [ 10 ] [ 11 ]  However, in December 2007, the  IRS  stated that full-body scans qualify as deductible medical expenses, without a doctor's referral. This will likely lead employer-sponsored, flexible-spending plans to make the cost of the scans eligible for reimbursement. [ 12 ]


Gynoroentgenology  is the abbreviation of  gynecological roentgenology . It is the  radiologic  imaging of the  gynecologic  parts of the  female   human body  in order to make a  radiologic   diagnosis  of a gynecologic disease.  The term  gynecologic radiology  is related to gynoroentgenology.   Gynoroentgenologic imaging  can detect and diagnose primary  neoplasms ,  metastasis , therapy-related  lesions ,  congenital  lesions,  inflammation , miscellaneous diseases, pseudolesions, normal variants, infection uterine arteriovenous  malformations  and  cystic   adenomyosis . [ 1 ]   An example procedure is  gynography .


Lymphography  is a  medical imaging  technique in which a  radiocontrast  agent is injected, and then an  X-ray  picture is taken to visualise structures of the  lymphatic system , including  lymph nodes ,  lymph ducts ,  lymphatic tissues ,  lymph capillaries  and  lymph vessels .  Lymphangiography  is the same procedure, used only to visualize the  lymph vessels . [ 1 ]  The x-ray film or image of the  lymphatic vessels  and  lymph nodes  is called a  lymphogram  or a  lymphangiogram .


Radiographs can be taken after injection of a  radiopaque  contrast medium into small lymphatic vessels (these are made visible by prior  subcutaneous injection  of patent blue dye). The resulting lymphogram is used to find the locations of large vessels and nodes, and to identify sites of blockage in lymphatic drainage.


Lymph nodes can also be detected via  radionuclide imaging  after injection of radioactive  colloids .  Macrophages   phagocytose  these foreign bodies and sequester in the nodes.


Lymphography is used to visualise the structures of the  lymphatic system , including  lymph nodes ,  lymph ducts ,  lymphatic tissues ,  lymph capillaries  and  lymph vessels . It can be used during thoracic duct embolisation. [ 2 ]


Lymphography is not commonly used in modern medicine since the adoption of  CT scan  and  PET scan  technologies. [ 1 ]


Lymphograhy is usually considered a very safe procedure. [ 3 ]  The most serious adverse reaction tends to be a possible  allergic reaction  to injected  contrast agent . [ 3 ]


Lymphography is often an invasive procedure. [ 1 ]  It may be difficult to access  lymphatic vessels , as they are usually very narrow and hard to locate. The procedure also takes a very long time to perform. [ 1 ]


A needle or  catheter  is inserted into a  lymphatic vessel  in either the  foot  or the  arm . A  contrast agent  is injected into the lymphatic vessel. [ 1 ]  This may be around 2 to 4  millilitres  of  iotrolan  or  iodixanol   solution . [ 3 ]  This is performed at a very slow rate of around 0.1 millilitres per  minute . [ 3 ]  This prevents damage to the lymphatic vessel and disrupting the normal rate of lymph flow. It can take approximately 60 to 90  minutes  for all the contrast medium to be injected. Once the contrast medium is injected, the catheter is removed, and the incisions are  stitched  and  bandaged .


A  fluoroscope  is used to follow the dye as it spreads through the lymphatic system through the  legs , into the  groin , and along the back of the  abdominal cavity .  X-rays  are taken of the legs,  pelvis ,  abdomen , and  thorax  areas. The next day, another set of X-rays may be taken.


If a site of  cancer  ( breast cancer  or  melanoma ) is being studied to evaluate spreading, a mixture of blue dye and a  radioactive  tracer is injected next to the mass. [ 3 ]  Special cameras detect the spread of tracer along lymph channels to outlying lymph nodes. A  surgeon  will then use the visible blue dye or radioactivity within nodes to guide  biopsy  within adjacent tissues (such as the arm pit for breast cancer) to determine possible routes of cancer spread. [ 3 ]


The name comes from the  Greek  words "Λέμφος" ("Lemphos")("lymph"), "water lymph", and "graphien" "Γραφή"("Graphy"), "to write or record".


Mammography  (also called  mastography ;  DICOM  modality: MG) is the process of using low-energy  X-rays  (usually around 30  kVp ) to examine the human  breast  for diagnosis and screening. The goal of mammography is the early detection of  breast cancer , typically through detection of characteristic masses,  microcalcifications , asymmetries, and distortions.


As with all X-rays, mammograms use doses of  ionizing radiation  to create images. These images are then analyzed for abnormal findings. It is usual to employ lower-energy X-rays, typically Mo (K-shell X-ray energies of 17.5 and 19.6 keV) and Rh (20.2 and 22.7 keV) than those used for  radiography  of  bones . Mammography may be 2D or 3D ( tomosynthesis ), depending on the available equipment or purpose of the examination.  Ultrasound ,  ductography ,  positron emission mammography  (PEM), and  magnetic resonance imaging  (MRI) are adjuncts to mammography. Ultrasound is typically used for further evaluation of masses found on mammography or palpable masses that may or may not be seen on mammograms. Ductograms are still used in some institutions for evaluation of bloody nipple discharge when the mammogram is non-diagnostic. MRI can be useful for the screening of high-risk patients, for further evaluation of questionable findings or symptoms, as well as for pre-surgical evaluation of patients with known breast cancer, in order to detect additional lesions that might change the surgical approach (for example, from breast-conserving  lumpectomy  to  mastectomy ).


In 2023, the  U.S. Preventive Services Task Force  issued a draft recommendation statement that all women should receive a screening mammography every two years from age 40 to 74. [ 1 ] [ 2 ]  The American College of Radiology, Society of Breast Imaging, and American Cancer Society recommend yearly screening mammography starting at age 40. [ 3 ]  The Canadian Task Force on Preventive Health Care (2012) and the European Cancer Observatory (2011) recommend mammography every 2 to 3 years between ages 50 and 69. [ 4 ] [ 5 ]  These task force reports point out that in addition to unnecessary surgery and anxiety, the risks of more frequent mammograms include a small but significant increase in breast cancer induced by radiation. [ 6 ] [ 7 ]  Additionally, mammograms should not be performed with increased frequency in patients undergoing breast surgery, including breast enlargement, mastopexy, and breast reduction. [ 8 ]


Digital mammography is a specialized form of mammography that uses digital receptors and computers instead of  X-ray  film to help examine  breast  tissue for  breast cancer . [ 9 ]  The electrical signals can be read on computer screens, permitting more manipulation of images to allow  radiologists  to view the results more clearly. [ 9 ] [ 10 ]  The standard digital mammography is "full field" (FFDM), in which the entire breast is imaged in a single view. [ 9 ]  Digital mammography can also include the use of "spot views", in which a paddle is used to further compress areas of concern. [ 11 ]


Digital mammography is also utilized in  stereotactic biopsy . Breast biopsy may also be performed using a different modality, such as  ultrasound  or  magnetic resonance imaging  (MRI).


While radiologists [ 12 ]  had hoped for more marked improvement, the effectiveness of digital mammography was found comparable to traditional X-ray methods in 2004, though there may be reduced radiation with the technique and it may lead to fewer retests. [ 9 ]   Specifically, it performs no better than film for post-menopausal women, who represent more than three-quarters of women with breast cancer. [ 13 ]  The U.S. Preventive Services Task Force concluded that there was insufficient evidence to recommend for or against digital mammography over basic film mammography for breast cancer screening. [ 14 ]


Digital mammography is a  NASA spin-off , utilizing technology developed for the  Hubble Space Telescope . [ 15 ]  As of 2022, over 99% of certified mammography centers in the United States screening centers use digital mammography. [ 16 ]  Globally, systems by  Fujifilm Corporation  are the most widely used. [ citation needed ]  In the United States, GE's digital imaging units typically cost US$300,000 to $500,000, far more than film-based imaging systems. [ 13 ]  Costs may decline as GE begins to compete with the less expensive  Fuji  systems. [ 13 ]


Three-dimensional mammography , also known as digital breast tomosynthesis (DBT),  tomosynthesis , and 3D breast imaging, is a mammogram technology that creates a 3D view of the breast using X-rays from different angles. Supplementing standard 2D mammography with DBT has been shown to improve cancer detection. [ 17 ]  Cost effectiveness is unclear as of 2016. [ 18 ]  Another concern is that it more than doubles the radiation exposure. [ 19 ]


Photon-counting mammography was introduced commercially in 2003 and was shown to reduce the X-ray dose to the patient by approximately 40% compared to conventional methods while maintaining image quality at an equal or higher level. [ 20 ]  The technology was subsequently developed to enable  spectral imaging  with the possibility to further improve image quality, to distinguish between different tissue types, [ 21 ]  and to measure breast density. [ 22 ] [ 23 ]


A galactography (or breast ductography) is a now infrequently used type of mammography used to visualize the milk ducts. Prior to the mammography itself, a radiopaque substance is injected into the duct system. This test is indicated when nipple discharge exists.


Mammography can detect cancer early when it’s most treatable and can be treated less invasively (thereby helping to preserve quality of life).


According to  National Cancer Institute  data, since mammography screening became widespread in the mid-1980s, the U.S. breast cancer death rate, unchanged for the previous 50 years, has dropped well over 30 percent. [ 24 ]  In European countries like Denmark and Sweden, where mammography screening programs are more organized, the breast cancer death rate has been cut almost in half over the last 20 years. [ as of? ]


Mammography screening cuts the risk of dying from breast cancer nearly in half. [ 25 ]  A recent study published in  Cancer  showed that more than 70 percent of the women who died from breast cancer in their 40s at major Harvard teaching hospitals were among the 20 percent of women who were not being screened. [ 26 ] [ unreliable medical source ]  Some scientific studies [ citation needed ]  have shown that the most lives are saved by screening beginning at age 40.


A recent study in the  British Medical Journal  shows that early detection of breast cancer – as with mammography – significantly improves breast cancer survival. [ 27 ]


The benefits of mammography screening at decreasing breast cancer mortality in randomized trials are not found in observational studies performed long after implementation of breast cancer screening programs (for instance, Bleyer et al. [ 28 ] )


In 2014, the Surveillance, Epidemiology, and End Results Program of the National Institutes of Health reported the occurrence rates of breast cancer based on 1000 women in different age groups. [ 29 ]  In the 40–44 age group, the incidence was 1.5 and in the 45–49 age group, the incidence was 2.3. [ 29 ]  In the older age groups, the incidence was 2.7 in the 50–54 age group and 3.2 in the 55–59 age group. [ 29 ]


While screening between ages 40 and 50 is somewhat controversial, the preponderance of the evidence indicates that there is a benefit in terms of early detection. Currently, the  American Cancer Society , the  American Congress of Obstetricians and Gynecologists (ACOG) , the  American College of Radiology , and the  Society of Breast Imaging  encourage annual mammograms beginning at age 40. [ 30 ] [ 31 ] [ 32 ]


The  National Cancer Institute  encourages mammograms every one to two years for women ages 40 to 49. [ 33 ]   In 2023,  United States Preventive Services Task Force  (USPSTF) revised the recommendation that women and transgender men undergo biennial mammograms starting at the age of 40, rather than the previously suggested age of 50. [ 34 ]  This adjustment is prompted by the increasing incidence of breast cancer in the 40 to 49 age group over the past decade.


In contrast, the  American College of Physicians , a large internal medicine group, has recently encouraged individualized screening plans as opposed to wholesale biannual screening of women aged 40 to 49. [ 35 ]  The  American Cancer Society  recommendations for women at average risk for breast cancer is a yearly mammogram from age 45 to 54 with an optional yearly mammogram from age 40 to 44. [ 36 ]


Women who are at high risk for early-onset breast cancer have separate recommendations for screening. These include those who:


The  American College of Radiology  recommends these individuals to get annual mammography starting at the age of 30. Those with a history of chest radiation therapy before age 30 should start annually at age 25 of 8 years after their latest therapy (whichever is latest). [ 38 ]  The  American Cancer Society  also recommends women at high risk should get a mammogram and breast MRI every year beginning at age 30 or an age recommended by their healthcare provider. [ 36 ]


The  National Comprehensive Cancer Network  (NCCN) advocates screening for women who possess a BRCA1 or BRCA2 mutation or have a first-degree relative with such a mutation, even in the absence of the patient being tested for BRCA1/2 mutations. For women at high risk, NCCN recommends undergoing an annual mammogram and breast MRI between the ages of 25 and 40, considering the specific gene mutation type or the youngest age of breast cancer occurrence in the family. Additionally, NCCN suggests that high-risk women undergo clinical breast exams every 6 to 12 months starting at age 25. These individuals should also engage in discussions with healthcare providers to assess the advantages and disadvantages of 3D mammography and acquire knowledge on detecting changes in their breasts. [ 39 ]


The radiation exposure associated with mammography is a potential risk of screening, which appears to be greater in younger women. In scans where women receive 0.25–20 Gray (Gy) of radiation, they have more of an elevated risk of developing breast cancer. [ 40 ]  A study of radiation risk from mammography concluded that for women 40 years of age and older, the risk of radiation-induced breast cancer was minuscule, particularly compared with the potential benefit of mammographic screening, with a benefit-to-risk ratio of 48.5 lives saved for each life lost due to radiation exposure. [ 41 ]  This also correlates to a decrease in breast cancer mortality rates by 24%. [ 40 ]


The mammography procedure can be painful. Reported pain rates range from 6–76%, with 23–95% experiencing pain or discomfort. [ 42 ]  Experiencing pain is a significant predictor in women not re-attending screening. [ 43 ]  There are few proven interventions to reduce pain in mammography, but evidence suggests that giving women information about the mammography procedure prior to it taking place may reduce the pain and discomfort experienced. [ 44 ]  Furthermore, research has found that standardised compression levels can help to reduce patients' pain while still allowing for optimal diagnostic images to be produced. [ 45 ]


During the procedure, the breast is compressed using a dedicated mammography unit. Parallel-plate compression evens out the thickness of breast  tissue  to increase image quality by reducing the thickness of tissue that X-rays must penetrate, decreasing the amount of scattered radiation (scatter degrades image quality), reducing the required radiation dose, and holding the breast still (preventing  motion blur ). In screening mammography, both head-to-foot (craniocaudal, CC) view and angled side-view (mediolateral oblique, MLO) images of the breast are taken. Diagnostic mammography may include these and other views, including geometrically magnified and spot-compressed views of the particular area of concern. [ citation needed ]   Deodorant [ citation needed ] ,  talcum powder [ 46 ]  or  lotion  may show up on the X-ray as  calcium  spots, so women are discouraged from applying them on the day of their exam. There are two types of mammogram studies: screening mammograms and diagnostic mammograms. Screening mammograms, consisting of four standard X-ray images, are performed yearly on patients who present with no symptoms. Diagnostic mammograms are reserved for patients with breast symptoms (such as palpable lumps, breast pain, skin changes, nipple changes, or nipple discharge), as follow-up for probably benign findings (coded BI-RADS 3), or for further evaluation of abnormal findings seen on their screening mammograms. Diagnostic mammograms may also performed on patients with personal or family histories of breast cancer. Patients with breast implants and other stable benign surgical histories generally do not require diagnostic mammograms.


Until some years ago, mammography was typically performed with screen-film cassettes. Today, mammography is undergoing transition to digital detectors, known as  digital mammography  or Full Field Digital Mammography (FFDM). The first FFDM system was approved by the FDA in the U.S. in 2000. This progress is occurring some years later than in general radiology. This is due to several factors:


As of March 1, 2010, 62% of facilities in the United States and its territories have at least one FFDM unit. [ 47 ]  (The FDA includes computed radiography units in this figure. [ 48 ] )


Tomosynthesis, otherwise known as 3D mammography, was first introduced in clinical trials in 2008 and has been  Medicare -approved in the United States since 2015. As of 2023, 3D mammography has become widely available in the US and has been shown to have improved sensitivity and specificity over 2D mammography.


Mammograms are either looked at by one (single reading) or two (double reading) trained professionals: [ 49 ]  these film readers are generally  radiologists , but may also be  radiographers ,  radiotherapists , or breast clinicians (non-radiologist physicians specializing in breast disease). [ 49 ]


Double reading significantly improves the  sensitivity and specificity  of the procedure, and is standard practice in the United Kingdom, but not in the United States as it is not reimbursed by Medicare or private  health insurance . This is despite multiple trials showing increased accuracy of detection and improved patient outcomes for both  morbidity  and  mortality  when double reading is employed. [ 49 ]   Clinical decision support systems  may be used with  digital mammography  (or digitized images from analogue mammography [ 50 ] ), but studies suggest these approaches do not significantly improve performance or provide only a small improvement. [ 49 ] [ 51 ]


Stratification for breast cancer risk on a mammogram is based on a reporting system known as Breast Imaging-Reporting and Data System ( BI-RADS ), developed by the  American College of Radiology  in 1993. It has five general categories of findings: mass, asymmetry, architectural distortion, calcifications, and associated features.


The use of language with BI-RADS is extremely precise, with a limited set of permissible adjectives for lesion margins, shape and internal density, each of which carries a different prognostic significance. Margins of a lesion, for example, can only be described as  circumscribed ,  obscured ,  micropapillary ,  indistinct  or  stellate . Similarly, shape can only be  round ,  oval  or  irregular . Each of these agreed upon adjectives is referred to as a "descriptor" in the BI-RADS lexicon, with specific  positive  and  negative predictive values  for breast cancer with each word. Additionally, each BI-RADS category corresponds with a probability of cancer. This fastiduous attention to semantics with BI-RADS allows for standardization of cancer detection across different treatment centers and imaging modalities. [ 52 ]


After describing the findings, the radiologist provides a final assessment ranging from 0 to 6:


BI-RADS 3, 4 and 5 assessments on  screening mammograms  require further investigation with a second "diagnostic" study. The latter is a more detailed mammogram that allows dedicated attention to the abnormal finding with additional maneuvers such as magnification, rolling of breast tissue or exaggerated positioning. There may also be imaging with  ultrasound  at this time, which carries its own parallel BI-RADS lexicon. Suspicious lesions are then  biopsied  with  local anesthesia  or proceed straight to surgery depending on their  staging .  [ 55 ]  Biopsy can be done with  the help of x-rays  or  ultrasound , depending on which imaging modality shows the lesion best. [ 56 ]


In the UK mammograms are scored on a scale from 1–5 (1 = normal, 2 = benign, 3 = indeterminate, 4 = suspicious of malignancy, 5 = malignant). Evidence suggests that accounting for genetic risk, factors improve breast cancer risk prediction. [ 57 ]


As a medical procedure that induces ionizing radiation, the origin of mammography can be traced to the discovery of X-rays by  Wilhelm Röntgen  in 1895.


In 1913, German surgeon  Albert Salomon  performed a mammography study on 3,000  mastectomies , comparing X-rays of the breasts to the actual removed tissue, observing specifically  microcalcifications . [ 58 ] [ 59 ]   By doing so, he was able to establish the difference as seen on an  X-ray  image between cancerous and non-cancerous tumors in the breast. [ 59 ]   Salomon's mammographs provided substantial information about the spread of tumors and their borders. [ 60 ]


In 1930, American physician and radiologist  Stafford L. Warren  published "A Roentgenologic Study of the Breast", [ 61 ]  a study where he produced  stereoscopic  X-rays images to track changes in breast tissue as a result of  pregnancy  and  mastitis . [ 62 ] [ 63 ]  In 119 women who subsequently underwent surgery, he correctly found breast cancer in 54 out of 58 cases. [ 62 ]


As early as 1937,  Jacob Gershon-Cohen  developed a form a mammography for a diagnostic of breast cancer at earlier stages to improve survival rates. [ 64 ]  In 1949, Raul Leborgne sparked renewed enthusiasm for mammography by emphasizing the importance of technical proficiency in patient positioning and the adoption of specific radiological parameters. He played a pioneering role in elevating imaging quality while placing particular emphasis on distinguishing between benign and malignant calcifications. [ 65 ]  In the early 1950s, Uruguayan radiologist Raul Leborgne developed the breast compression technique to produce better quality images, and described the differences between benign and malign microcalcifications. [ 66 ]


In 1956, Gershon-Cohen conducted clinical trails on over 1,000 asymptomatic women at the  Albert Einstein Medical Center  on his screening technique, [ 64 ]  and the same year, Robert Egan at the  University of Texas M.D. Anderson Cancer Center  combined a technique of low kVp with high mA and single emulsion films developed by  Kodak  to devise a method of screening mammography. He published these results in 1959 in a paper, subsequently vulgarized in a 1964 book called  Mammography . [ 67 ]  The "Egan technique", as it became known, enabled physicians to detect calcification in breast tissue; [ 68 ]  of the 245 breast cancers that were confirmed by biopsy among 1,000 patients, Egan and his colleagues at M.D. Anderson were able to identify 238 cases by using his method, 19 of which were in patients whose physical examinations had revealed no breast pathology.


Use of mammography as a screening technique spread clinically after a 1966 study demonstrating the impact of mammograms on mortality and treatment led by  Philip Strax . This study, based in New York, was the first large-scale randomized controlled trial of mammography screening. [ 69 ] [ 70 ]


In 1985,  László Tabár  and colleagues documented findings from mammographic screening involving 134,867 women aged 40 to 79. Using a single mediolateral oblique image, they reported a 31% reduction in mortality. [ 65 ]  Dr. Tabár has since written many publications promoting mammography in the areas of epidemiology, screening, early diagnosis, and clinical-radiological-pathological correlation.


The use of mammography as a screening tool for the detection of early breast cancer in otherwise healthy women without symptoms is seen by some as controversial. [ 71 ] [ 72 ] [ 73 ]


Keen and Keen indicated that repeated mammography starting at age fifty saves about 1.8 lives over 15 years for every 1,000 women screened. [ 74 ]  This result has to be weighed against the adverse effects of errors in diagnosis,  over-treatment , and radiation exposure.


The Cochrane analysis of screening indicates that it is "not clear whether screening does more good than harm". According to their analysis, 1 in 2,000 women will have her life prolonged by 10 years of screening, while 10 healthy women will undergo unnecessary breast cancer treatment. Additionally, 200 women will experience significant psychological stress due to false positive results. [ 75 ]


The  Cochrane Collaboration  (2013) concluded after ten years that trials with adequate randomization did not find an effect of mammography screening on total cancer mortality, including breast cancer. The authors of this Cochrane review write: "If we assume that screening reduces breast cancer mortality by 15% and that overdiagnosis and over-treatment is at 30%, it means that for every 2,000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress including anxiety and uncertainty for years because of false positive findings." The authors conclude that the time has come to re-assess whether universal mammography screening should be recommended for any age group. [ 75 ]  They state that universal screening may not be reasonable. [ 76 ]  The Nordic Cochrane Collection updated research in 2012 and stated that advances in diagnosis and treatment make mammography screening less effective today, rendering it "no longer effective". They conclude that "it therefore no longer seems reasonable to attend" for breast cancer screening at any age, and warn of misleading information on the internet. [ 76 ]


Newman posits that screening mammography does not reduce death overall, but causes significant harm by inflicting cancer scare and unnecessary surgical interventions. [ 77 ]  The Nordic Cochrane Collection notes that advances in diagnosis and treatment of breast cancer may make breast cancer screening no longer effective in decreasing death from breast cancer, and therefore no longer recommend routine screening for healthy women as the risks might outweigh the benefits. [ 76 ]


Of every 1,000 U.S. women who are screened, about 7% will be called back for a diagnostic session (although some studies estimate the number to be closer to 10% to 15%). [ 78 ]   About 10% of those who are called back will be referred for a biopsy. Of the 10% referred for biopsy, about 3.5% will have cancer and 6.5% will not. Of the 3.5% who have cancer, about 2 will have an early stage cancer that will be cured after treatment.


Mammography may also produce false negatives. Estimates of the numbers of cancers missed by mammography are usually around 20%. [ 79 ]   Reasons for not seeing the cancer include observer error, but more frequently it is because the cancer is hidden by other dense tissue in the breast, and even after retrospective review of the mammogram the cancer cannot be seen. Furthermore, one form of breast cancer, lobular cancer, has a growth pattern that produces shadows on the mammogram that are indistinguishable from normal breast tissue.


The  Cochrane Collaboration  states that the best quality evidence does not demonstrate a reduction in mortality or a reduction in mortality from all types of cancer from screening mammography. [ 75 ]


The Canadian Task Force found that for women ages 50 to 69, screening 720 women once every 2 to 3 years for 11 years would prevent one death from breast cancer. For women ages 40 to 49, 2,100 women would need to be screened at the same frequency and period to prevent a single death from breast cancer. [ 4 ]


Women whose breast cancer was detected by screening mammography before the appearance of a lump or other symptoms commonly assume that the mammogram "saved their lives". [ 80 ]  In practice, the vast majority of these women received no practical benefit from the mammogram. There are four categories of cancers found by mammography:


Only 3% to 13% of breast cancers detected by screening mammography will fall into this last category. Clinical trial data suggests that 1 woman per 1,000 healthy women screened over 10 years falls into this category. [ 80 ]  Screening mammography produces no benefit to any of the remaining 87% to 97% of women. [ 80 ]  The probability of a woman falling into any of the above four categories varies with age. [ 81 ] [ 82 ]


A 2016 review for the  United States Preventive Services Task Force  found that mammography was associated with an 8%-33% decrease in breast cancer mortality in different age groups, but that this decrease was not  statistically significant  at the age groups of 39–49 and 70–74. The same review found that mammography significantly decreased the risk of advanced cancer among women aged 50 and older by 38%, but among those aged 39 to 49 the risk reduction was a non-significant 2%. [ 83 ]  The USPSTF made their review based on data from randomized controlled trials (RCT) studying breast cancer in women between the ages of 40-49. [ 29 ]


The goal of any screening procedure is to examine a large population of patients and find the small number most likely to have a serious condition. These patients are then referred for further, usually more invasive, testing. Thus a screening exam is not intended to be definitive; rather it is intended to have sufficient sensitivity to detect a useful proportion of cancers. The cost of higher sensitivity is a larger number of results that would be regarded as suspicious in patients without disease. This is true of mammography. The patients without disease who are called back for further testing from a screening session (about 7%) are sometimes referred to as " false positives ". There is a trade-off between the number of patients with disease found and the much larger number of patients without disease that must be re-screened. [ citation needed ]


Research shows [ 84 ]  that false-positive mammograms may affect women's well-being and behavior. Some women who receive false-positive results may be more likely to return for routine screening or perform breast self-examinations more frequently. However, some women who receive false-positive results become anxious, worried, and distressed about the possibility of having breast cancer, feelings that can last for many years. [ citation needed ]


False positives also mean greater expense, both for the individual and for the screening program. Since follow-up screening is typically much more expensive than initial screening, more false positives (that must receive follow-up) means that fewer women may be screened for a given amount of money. Thus as sensitivity increases, a screening program will cost more or be confined to screening a smaller number of women. [ citation needed ]


The central harm of mammographic breast cancer screening is  overdiagnosis : the detection of abnormalities that meet the pathologic definition of cancer but will never progress to cause symptoms or death. Dr.  H. Gilbert Welch , a researcher at Dartmouth College, states that "screen-detected breast and prostate cancer survivors are more likely to have been over-diagnosed than actually helped by the test." [ 80 ]  Estimates of overdiagnosis associated with mammography have ranged from 1% to 54%. [ 85 ]  In 2009,  Peter C. Gotzsche  and Karsten Juhl Jørgensen reviewed the literature and found that 1 in 3 cases of breast cancer detected in a population offered mammographic screening is over-diagnosed. [ 86 ]  In contrast, a 2012 panel convened by the national cancer director for England and  Cancer Research UK  concluded that 1 in 5 cases of breast cancer diagnosed among women who have undergone breast cancer screening are over-diagnosed. This means an over-diagnosis rate of 129 women per 10,000 invited to screening. [ 87 ]  A recent systematic review of 30 studies found that screening mammography for breast cancer among women aged 40 years and older was 12.6%. [ 88 ]


Mammograms also have a rate of missed tumors, or "false negatives". Accurate data regarding the number of false negatives are very difficult to obtain because  mastectomies  cannot be performed on every woman who has had a mammogram to determine the false negative rate. Estimates of the false negative rate depend on close follow-up of a large number of patients for many years. This is difficult in practice because many women do not return for regular mammography making it impossible to know if they ever developed a cancer. In his book  The Politics of Cancer , Dr. Samuel S. Epstein claims that in women ages 40 to 49, one in four cancers are missed at each mammography. Researchers have found that breast tissue is denser among younger women, making it difficult to detect tumors. For this reason, false negatives are twice as likely to occur in pre-menopausal mammograms (Prate). This is why the screening program in the UK does not start calling women for screening mammograms until age 50. [ 89 ]


The importance of these missed cancers is not clear, particularly if the woman is getting yearly mammograms. Research on a closely related situation has shown that small cancers that are not acted upon immediately, but are observed over periods of several years, will have good outcomes. A group of 3,184 women had mammograms that were formally classified as "probably benign". This classification is for patients who are not clearly normal but have some area of minor concern. This results not in the patient being biopsied, but rather in having early follow up mammography every six months for three years to determine whether there has been any change in status. Of these 3,184 women, 17 (0.5%) did have cancers. Most importantly, when the diagnosis was finally made, they were all still stage 0 or 1, the earliest stages. Five years after treatment, none of these 17 women had evidence of re-occurrence. Thus, small early cancers, even though not acted on immediately, were still reliably curable. [ 90 ]


Breast cancer imposes a significant economic strain on communities, with the expense of treating stages three and four in the United States in 2017 amounting to approximately $127,000. [ 91 ]  While early diagnosis and screening methods are important in reducing the death rates, the cost-benefit of breast cancer screening using mammography has been unclear. A recent systematic review of three studies held in Spain, Denmark, and the United States from 2000-2019 found that digital mammography is not cost-beneficial for the healthcare system when compared to other screening methods. Therefore, increasing its frequency may cause higher costs on the healthcare system. While there may be a lack of evidence, it is suggested that digital mammography be performed every two years for ages over 50. [ 92 ]


As the  USPSTF  recommendations are so influential, changing mammography screenings from 50 to 40 years of age has significant implications to public health. The major concerns regarding this update is whether breast cancer mortality has truly been increasing and if there is new evidence that the benefits of mammography are increasing. [ 93 ]


According to  National Vital Statistics System , mortality from breast cancer has been steadily decreasing in the United States from 2018 to 2021. There have also been no new randomized trials of screening mammography for women in their 40s since the previous USPSTF recommendation was made. In addition, the 8 most recent randomized trials for this age group revealed no significant effect. [ 94 ]  Instead, the  USPSTF  used statistical models to estimate what would happen if the starting age were lowered, assuming that screening mammography reduces breast cancer mortality by 25%. This found that screening 1,000 women from 40–74 years of age, instead of 50-74, would cause 1-2 fewer breast cancer deaths per 1,000 women screened over a lifetime. [ 95 ]


Approximately 75 percent of women diagnosed with breast cancer have no family history of breast cancer or other factors that put them at high risk for developing the disease (so screening only high-risk women misses majority of cancers). An analysis by Hendrick and Helvie, [ 96 ]  published in the  American Journal of Roentgenology , showed that if USPSTF breast cancer screening guidelines were followed, approximately 6,500 additional women each year in the U.S. would die from breast cancer.


The largest (Hellquist et al) [ 97 ]  and longest running (Tabar et al) [ 98 ]  breast cancer screening studies in history re-confirmed that regular mammography screening cut breast cancer deaths by roughly a third in all women ages 40 and over (including women ages 40–49). This renders the USPSTF calculations off by half. They used a 15% mortality reduction to calculate how many women needed to be invited to be screened to save a life. With the now re-confirmed 29% (or up) figure, the number to be screened using the USPSTF formula is half of their estimate and well within what they considered acceptable by their formula.


Many factors affect how many people attend breast cancer screenings. For example, people from minority  ethnic communities  are also less likely to attend cancer screening. In the UK, women of  South Asian heritage  are the least likely to attend breast cancer screening. Research is still needed to identify specific barriers for the different South Asian communities. For example, a study showed that  British-Pakistani  women faced cultural and  language barriers  and were not aware that breast screening takes place in a female-only environment. [ 99 ] [ 100 ] [ 101 ]


People with  mental illnesses  are also less likely to attend cancer screening appointments. [ 102 ] [ 103 ]  In Northern Ireland women with mental health problems were shown to be less likely to attend  screening for breast cancer , than women without. The lower attendance numbers remained the same even when marital status and  social deprivation  were taken into account. [ 104 ] [ 105 ]


Mammography facilities in the United States and its territories (including military bases) are subject to the  Mammography Quality Standards Act  (MQSA). The act requires annual inspections and accreditation every three years through an FDA-approved body. Facilities found deficient during the inspection or accreditation process can be barred from performing mammograms until corrective action has been verified or, in extreme cases, can be required to notify past patients that their exams were sub-standard and should not be relied upon. [ 106 ]


At this time, [ when? ]  MQSA applies only to traditional mammography and not to related scans, such as  breast ultrasound , stereotactic breast biopsy, or breast MRI.


As of September 10, 2024, the MQSA requires that all patients be notified of their breast density ("dense" or "not dense") in their mammogram reports. [ 107 ] [ 108 ]


Recently,  artificial intelligence (AI)  programs have been developed to utilize features from screening mammography images to predict breast cancer risk. A systematic review of 16 retrospective study designs comparing median maximum  AUC  found that artificial intelligence had a comparable or better accuracy (AUC = 0.72) of predicting breast cancer than clinical risk factors alone (AUC = 0.61), suggesting a transition from clinical risk factor-based to AI image-based risk models may lead to more accurate and personalized risk-based screening approaches. [ 109 ]


Another study of 32 published papers involving 23,804 mammograms and various machine learning methods ( CNN ,  ANN , and  SVM ) found promising results in the ability to assist clinicians in large-scale population-based breast cancer screening programs. [ 110 ]


For patients who do not want to undergo mammography, MRI and also breast computed tomography (also called breast CT) offer a painless alternative. Whether the respective method is suitable depends on the clinical picture; it is decided by the physician. [ citation needed ]


A  panoramic radiograph  is a  panoramic  scanning  dental X-ray  of the upper and lower  jaw . It shows a  two-dimensional  view of a  half-circle  from  ear  to ear. Panoramic radiography is a form of  focal plane tomography ; thus, images of multiple  planes  are taken to make up the composite panoramic image, where the  maxilla  and  mandible  are in the focal trough and the structures that are superficial and deep to the trough are blurred.


Other nonproprietary names for a panoramic radiograph are  dental panoramic radiograph  and  pantomogram ; Abbreviations include  PAN ,  DPR ,  OPT , and  OPG  (the latter, based on genericizing a trade name, are often avoided in medical editing).


Dental  panoramic   radiography  equipment consists of a horizontal rotating arm which holds an X-ray source and a moving  film  mechanism (carrying a film) arranged at opposed extremities. The patient's  skull  sits between the X-ray generator and the film. The  X-ray  source is rectangular  collimated  beam. [ 1 ]  Also the height of that beam covers the  mandibles  and the  maxilla  regions. The arm moves and its movement may be described as a rotation around an instant center which shifts on a dedicated  trajectory .


The manufacturers propose different solutions for moving the arm, trying to maintain constant distance between the teeth to the film and generator. Also those moving solutions try to project the teeth  arch  as  orthogonally  as possible. It is impossible to select an ideal movement as the anatomy varies very much from person to person. Finally a  compromise  is selected by each manufacturer and results in  magnification  factors which vary strongly along the film (15%-30%). The patient positioning is very critical in regard to both sharpness and distortions. [ citation needed ]


There are two kinds of film moving mechanisms, one using a sliding flat  cassette  which holds the film, and another using a rotating cylinder around which the film is wound. There are two standard sizes for dental panoramic films: 30 cm × 12 cm (12″ × 5″) and 30 cm x 15 cm (12″ × 6″). The smaller size film receives 8% less X-ray  dosage  on it compared to the bigger size.


Dental X-rays' radiology is moving from film technology (involving a chemical developing process) to  digital X-ray  technology, which is based on electronic sensors and  computers . One of the principal advantages compared to film based systems is the much greater  exposure latitude . This means many fewer repeated scans, which reduces costs and also reduces patient exposure to  radiation . Lost X-rays can also be reprinted if the digital file is saved. Other significant advantages include instantly viewable images, the ability to enhance images, the ability to email images to practitioners and clients (without needing to digitize them first), easy and reliable document handling, reduced X-ray exposure, that no  darkroom  is required, and that no  chemicals  are used.


One particular type of digital system uses a  photostimulable phosphor plate  (aka PSP - Phosphor Plate) in place of the film. After X-ray exposure the plate (sheet) is placed in a special  scanner  where the  latent  formed image is retrieved point by point and  digitized , using a laser light scanning. The digitized images are stored and displayed on the computer screen. This method is in between old film based technology and the current direct digital imaging technology. It is similar to the film process because it involves the same image support handling and differs because the chemical development process is replaced by the scanning process. This is not much faster than film processing and the  resolution  and sensitivity performances are contested. However it has the clear advantage of being able to fit with any existing equipment without any modification because it replaces just the existing film.


Also sometimes the term "digital X-rays" is used to designate the scanned film documents which further are handled by computers.


The other types of digital imaging technologies use electronic sensors. A majority of them first convert the X-rays in light (using a GdO2S or  CsI  layer) which is further captured using a  CCD  or a  CMOS  image sensor. Few of them use a hybrid  analog-to-digital  arrangement which first converts the X-ray into  electricity  (using a  CdTe  layer) and then this electricity is rendered as an image by a reading section based on CMOS technology.


In current state-of-the-art digital systems, the image quality is vastly superior to conventional film-based systems. The latest advancements have also seen the addition on Cone Beam 3D Technology to standard digital panoramic devices.


Orthopantomograms (OPTs) are used by health care professionals to provide information on:


Normally, the person bites on a plastic  spatula  so that all the teeth, especially the  crowns , can be viewed individually. The whole orthopantomogram process takes about one  minute . The patient's actual radiation exposure time varies between 5.5 and 22 seconds for the machine's excursion around the skull.