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A computed tomography (CT) scan, commonly referred to as a CT, is a radiological imaging study. The machine was developed by physicist Allan MacLeod Cormack and electrical engineer Godfrey Hounsfield.[1][2][3] Their development awarded them the Nobel Prize in Physiology or Medicine in 1979.[4] The first scanners were installed in 1974. Since then, technological advances and math have allowed single images to be computed into two-dimensional informative images. The CT scan is essentially an X-ray study, where a series of rays are rotated around a specified body part, and computer-generated cross-sectional images are produced. The advantage of these tomographic images compared to conventional x-rays is that they contain detailed information about a specified area in cross-section, eliminating the superimposition of images, which provides a tremendous advantage over plain films. CT scans provide excellent clinicopathological correlation for a suspected illness.[5][6] CT scan augments the physician's ability to diagnose a patient's illness accurately. Low-dose CT scans are proving useful in preventative medicine and cancer screening. The study was initially called a CAT scan representing computer axial tomography, where the table moved after each axial image was obtained.[7][8][9] In a spiral or helical scan, the table moves continuously as the x-ray source and detectors rotate. This reduces the duration of the study significantly to provide quick results in emergent situations. It rapidly substituted cerebral angiography for detecting head trauma injuries and brain masses in a fast and extremely reliable way.[10][11][12] A radiologic technician acquires CT scans, which are interpreted and reported by a trained radiologist.

The CT scan involves ionizing radiation, which has the potential to cause biological tissue harm.[30][31][32][33][34][35][36] CT scans can have 50 to 1000 times higher radiation dose than conventional X-rays.[31][37] They account for the largest portion of radiation after natural/environmental sources to the population. CT scans comprise approximately 50% of all medical radiation.[37][38][39] It has been estimated that for every 1 mSv of exposure, there is a 0.005% risk of developing fatal cancer. Thus, a radiation dose of 100 mSv will have a 0.5% risk of cancer.[40] Roughly 1 fatal cancer is developed for every 1000 CT scans performed on a pediatric patient.[41] Utilizing the atomic bomb data, the lifetime risk of leukemia from one pediatric head CT scan is approximately 1 in 10,000, and for brain cancer is approximately 1 in 2000 to 10,000.[34][35][42][43] This radiation exposure is especially critical in pediatric patients due to the developing organs' vulnerability when performed under ten years and the cumulative lifelong exposure.[44][45][46] Exposure should be limited following the "as low as reasonably achievable" principle. Multiple examinations should be avoided. They should be done if the benefit by far outweighs the risk.[30] The radiation dose of a CT scan ranges from 1 mSv to 27.0 mSv. (1 mSv= 1 mGy.) Natural/environmental exposure is approximately 3 mSv per year.[44] An adult abdominal CT exposes the patient to 10 mSv; however, during a neonatal abdominal CT, the exposure is 20 mSv.[31] Contrast agents may cause allergic reactions, usually mild, involving itching rash; however, severe reactions can occur, such as bronchospasm and anaphylactic reaction.[47][48][49][50] The probability of a fatal reaction is about 1 in 100,000. If the patient has an iodine allergy, steroids must be given to counteract any potential side effects if contrast must be given.[51] Kidney failure due to the iodine contrast material can occur in 2% to 7%, with greater risk in those with preexisting kidney disease.[52][53][54][55][56] Contrast-induced nephropathy, when severe, can require dialysis to clear the dye. In non-serious conditions, adequate hydration before the post-contrast injection will eliminate contrast from the body.