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The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography (CT), first defined in 1981. [ 1 ] [ 2 ] The unit of CTDI is the gray (Gy) and it can be used in conjunction with patient size to estimate the absorbed dose .
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.
The radiation used in CT scans can damage body cells, including DNA molecules, which can lead to radiation-induced cancer. [148] The radiation doses received from CT scans is variable. Compared to the lowest dose X-ray techniques, CT scans can have 100 to 1,000 times higher dose than conventional X-rays. [149]
Effective dose in adults [1] Equivalent time of background radiation [1] CT of the head: Single series: 2 mSv: 8 months With + without radiocontrast: 4 mSv: 16 months Chest: CT of the chest: 7 mSv: 2 years CT of the chest, lung cancer screening protocol: 1.5 mSv: 6 months Chest X-ray: 0.1 mSv: 10 days Heart: Coronary CT angiography: 12 mSv: 4 ...
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning.Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1,000 of a rem and 1 rem equals 0.01 Sv.
The average radiation dose from an abdominal X-ray is 0.7 millisieverts (0.0007 Sv), that from an abdominal CT scan is 8 mSv, that from a pelvic CT scan is 6 mGy, and that from a selective CT scan of the abdomen and the pelvis is 14 mGy. [7]
The information from a prior CT scan of the patient allows more accurate modelling of the behaviour of the radiation as it travels through the patient's tissues. Different dose calculation models are available, including pencil beam , convolution-superposition and monte carlo simulation , with precision versus computation time being the ...
The currently used low dose CT scan results in a radiation exposure of about 2 millisieverts (equal to roughly 20 two-view chest x-rays). [11] It has been estimated that radiation exposure from repeated screening studies could induce cancer formation in a small percentage of screened subjects, so this risk should be mitigated by a (relatively ...