ct scan ct scan a computed tomography scan (usually abbreviated to ct scan; formerly called computed axial tomography scan or cat scan) is a medical imaging technique used to obtain detailed internal images of the body. the personnel that perform ct scans are called radiographers or radiology technologists. this article is about x-ray computed tomography as used in medicine. for cross-sectional images used in industry, see industrial computed tomography. for means of tomography other than x-ray, see tomography. ct scanmodern ct scanner (2021), photon-counting ct (siemens naeotom alpha)other namesx-ray computed tomography (x-ray ct), computerized axial tomography scan (cat scan), computer aided tomography, computed tomography scanicd-10-pcsb?2icd-9-cm88.38meshd014057ops-301 code3–20...3–26medlineplus003330 ct scanners use a rotating x-ray tube and a row of detectors placed in a gantry to measure x-ray attenuations by different tissues inside the body. the multiple x-ray measurements taken from different angles are then processed on a computer using tomographic reconstruction algorithms to produce tomographic (cross-sectional) images (virtual "slices") of a body. ct scan can be used in patients with metallic implants or pacemakers, for whom magnetic resonance imaging (mri) is contraindicated. since its development in the 1970s, ct scanning has proven to be a versatile imaging technique. while ct is most prominently used in medical diagnosis, it can also be used to form images of non-living objects. the 1979 nobel prize in physiology or medicine was awarded jointly to south african-american physicist allan macleod cormack and british electrical engineer godfrey hounsfield "for the development of computer-assisted tomography". types on the basis of image acquisition and procedures various type of scanners are available in the market. sequential ct sequential ct also known as step-and-shoot ct is a type of scanning method in which the ct table moves stepwise. the table increments to a particular location and then stops which is followed by the x-ray tube rotation and acquisition of a slice. then the table increments again and another slice is taken. the table has to make a stop in taking slices. this results in increased time of scanning. spiral ct drawing of ct fan beam and patient in a ct imaging system ct scan of the thorax. the axial slice (right) is the image that corresponds to number 33 (left). spinning tube, commonly called spiral ct, or helical ct, is an imaging technique in which an entire x-ray tube is spun around the central axis of the area being scanned. these are the dominant type of scanners on the market because they have been manufactured longer and offer a lower cost of production and purchase. the main limitation of this type of ct is the bulk and inertia of the equipment (x-ray tube assembly and detector array on the opposite side of the circle) which limits the speed at which the equipment can spin. some designs use two x-ray sources and detector arrays offset by an angle, as a technique to improve temporal resolution. electron beam tomography main article: electron beam computed tomography electron beam tomography (ebt) is a specific form of ct in which a large enough x-ray tube is constructed so that only the path of the electrons, travelling between the cathode and anode of the x-ray tube, are spun using deflection coils. this type had a major advantage since sweep speeds can be much faster, allowing for less blurry imaging of moving structures, such as the heart and arteries. fewer scanners of this design have been produced when compared with spinning tube types, mainly due to the higher cost associated with building a much larger x-ray tube and detector array and limited anatomical coverage. dual energy ct dual energy ct also known as spectral ct is an advancement of computed tomography in which two energies are used to create two sets of data. a dual energy ct may employ dual source, single source with dual detector layer, single source with energy switching methods to get two different sets of data. dual source ct is an advanced scanner with a two x-ray tube detector system, unlike conventional single tube systems. these two detector systems are mounted on a single gantry at 90° in the same plane. dual source ct scanner allow fast scanning with higher temporal resolution by acquiring a full ct slice in only half a rotation. fast imaging reduces 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. single source with energy switching is another mode of dual energy ct in which a single tube is operated at two different energies by switching the energies frequently. ct perfusion imaging ct perfusion imaging is a specific form of ct to assess flow through blood vessels whilst injecting a contrast agent. blood flow, blood transit time, and organ blood volume, can all be calculated with reasonable sensitivity and specificity. this type of ct may be used on the heart, although sensitivity and specificity for detecting abnormalities are still lower than for other forms of ct. this may also be used on the brain, where ct perfusion imaging can often detect poor brain perfusion well before it is detected using a conventional spiral ct scan. this is better for stroke diagnosis than other ct types. pet ct main article: pet-ct pet-ct scan of chest positron emission tomography–computed tomography is a hybrid ct modality which combines, in a single gantry, a positron emission tomography (pet) scanner and an x-ray computed tomography (ct) scanner, to acquire sequential images from both devices in the same session, which are combined into a single superposed (co-registered) image. thus, functional imaging obtained by pet, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by ct scanning. pet-ct gives both anatomical and functional details of an organ under examination and is helpful in detecting different type of cancers. medical use since its introduction in the 1970s, ct has become an important tool in medical imaging to supplement conventional x-ray imaging and medical ultrasonography. it has more recently been used for preventive medicine or screening for disease, for example, ct colonography for people with a high risk of colon cancer, or full-motion heart scans for people with a high risk of heart disease. several institutions offer full-body scans for the general population although this practice goes against the advice and official position of many professional organizations in the field primarily due to the radiation dose applied. the use of ct scans has increased dramatically over the last two decades in many countries. an estimated 72 million scans were performed in the united states in 2007 and more than 80 million in 2015. head main article: computed tomography of the head computed tomography of human brain, from base of the skull to top. taken with intravenous contrast medium. ct scanning of the head is typically used to detect infarction (stroke), tumors, calcifications, haemorrhage, and bone trauma. of the above, hypodense (dark) structures can indicate edema and infarction, hyperdense (bright) structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows. tumors can be detected by the swelling and anatomical distortion they cause, or by surrounding edema. ct scanning of the head is also used in ct-guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations, and other surgically treatable conditions using a device known as the n-localizer. neck contrast ct is generally the initial study of choice for neck masses in adults. ct of the thyroid plays an important role in the evaluation of thyroid cancer. ct scan often incidentally finds thyroid abnormalities, and so is often the preferred investigation modality for thyroid abnormalities. lungs a ct scan can be used for detecting both acute and chronic changes in the lung parenchyma, the tissue of the lungs. it is particularly relevant here because normal two-dimensional x-rays do not show such defects. a variety of techniques are used, depending on the suspected abnormality. for evaluation of chronic interstitial processes such as emphysema, and fibrosis, thin sections with high spatial frequency reconstructions are used; often scans are performed both on inspiration and expiration. this special technique is called high resolution ct that produces a sampling of the lung, and not continuous images. hrct images of a normal thorax in axial, coronal and sagittal planes, respectively. bronchial wall thickness (t) and diameter of the bronchus (d) bronchial wall thickening can be seen on lung cts and generally (but not always) implies inflammation of the bronchi. an incidentally found nodule in the absence of symptoms (sometimes referred to as an incidentaloma) may raise concerns that it might represent a tumor, either benign or malignant. perhaps persuaded by fear, patients and doctors sometimes agree to an intensive schedule of ct scans, sometimes up to every three months and beyond the recommended guidelines, in an attempt to do surveillance on the nodules. however, established guidelines advise that patients without a prior history of cancer and whose solid nodules have not grown over a two-year period are unlikely to have any malignant cancer. for this reason, and because no research provides supporting evidence that intensive surveillance gives better outcomes, and because of risks associated with having ct scans, patients should not receive ct screening in excess of those recommended by established guidelines. angiography example of a ctpa, demonstrating a saddle embolus (dark horizontal line) occluding the pulmonary arteries (bright white triangle) main article: computed tomography angiography computed tomography angiography (cta) is a type of contrast ct to visualize the arteries and veins throughout the body. this ranges from arteries serving the brain to those bringing blood to the lungs, kidneys, arms and legs. an example of this type of exam is ct pulmonary angiogram (ctpa) used to diagnose pulmonary embolism (pe). it employs computed tomography and an iodine-based contrast agent to obtain an image of the pulmonary arteries. cardiac a ct scan of the heart is performed to gain knowledge about cardiac or coronary anatomy. traditionally, cardiac ct scans are used to detect, diagnose, or follow up coronary artery disease. more recently ct has played a key role in the fast-evolving field of transcatheter structural heart interventions, more specifically in the transcatheter repair and replacement of heart valves. the main forms of cardiac ct scanning are: coronary ct angiography (ccta): the use of ct to assess the coronary arteries of the heart. the subject receives an intravenous injection of radiocontrast, and then the heart is scanned using a high-speed ct scanner, allowing radiologists to assess the extent of occlusion in the coronary arteries, usually to diagnose coronary artery disease. coronary ct calcium scan: also used for the assessment of severity of coronary artery disease. specifically, it looks for calcium deposits in the coronary arteries that can narrow arteries and increase the risk of a heart attack. a typical coronary ct calcium scan is done without the use of radiocontrast, but it can possibly be done from contrast-enhanced images as well. to better visualize the anatomy, post-processing of the images is common. most common are multiplanar reconstructions (mpr) and volume rendering. for more complex anatomies and procedures, such as heart valve interventions, a true 3d reconstruction or a 3d print is created based on these ct images to gain a deeper understanding. abdomen and pelvis ct scan of a normal abdomen and pelvis, in sagittal plane, coronal and axial planes, respectively. main article: computed tomography of the abdomen and pelvis ct is an accurate technique for diagnosis of abdominal diseases like crohn's disease, git bleeding, and diagnosis and staging of cancer, as well as follow-up after cancer treatment to assess response. it is commonly used to investigate acute abdominal pain. non-enhanced computed tomography is today the gold standard for diagnosing urinary stones. the size, volume and density of stones can be estimated to help clinicians guide further treatment; size is especially important in predicting spontaneous passage of a stone. axial skeleton and extremities for the axial skeleton and extremities, ct is often used to image complex fractures, especially ones around joints, because of its ability to reconstruct the area of interest in multiple planes. fractures, ligamentous injuries, and dislocations can easily be recognized with a 0.2 mm resolution. with modern dual-energy