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Dose reference level is the level used for the dose that does not lead to adverse effects .
usually studies in this field using multiple dose including overdose.
In the case of several studies that deal with different effects the lowest level is determined that does not cause significant damage, then the level is divided along with the differences in sensitivity among Humans .
The processes and steps towards establishing DRLs are likely to involve many players, including the imaging facilities, the health authority, the professional bodies, and the regulatory body. In particular there should be collective ‘ownership’ of the DRLs in deciding on what procedures and what size groups will be used, how the data will be collected, who will manage the data, and when the DRLs should be reviewed and updated.

CT has been utilized for a) coronary angiography (coronary CTA) and b) coronary calcium scoring. The coronary arteries had conventionally been visualized using invasive coronary angiography that requires inserting a very small tube (catheter) into a blood vessel in the groin or arm, injecting a contrast agent when the catheter tip is at a desired location, and taking pictures under X-ray guidance. The coronary arteries can alternatively be visualized using modern CT scanning. This is usually done with multi-detector CT (MDCT) but was earlier also done with electron beam CT (EBCT).

Similarly coronary calcification scoring is done either using MDCT (earlier also with EBCT). Coronary calcification is usually defined as a plaque of at least 3 consecutive pixels (typical area of about 1 mm2 ) with a density of more than or equal to 130 Hounsfield units. For many current CT angiographic applications, 16 slice MDCT scanners are the minimum level of technology needed and 64 slice scanners are needed for good visualization of lesions. Current studies indicate that 64 slice CT angiography is highly accurate for exclusion of significant coronary artery stenosis (> 50% luminal narrowing) with negative predictive values in excess of 95% unless there is heavy arterial calcification.

There are clearly opportunities for dose reduction with almost any type of CT scan. For cardiac CT specifically, use of body weight-adapted MDCT protocols has been shown to reduce the effective dose by about 12% in males and 25% in females. Careful consideration of technical factors like kVp, mAs or scan length is effective. In addition, studies with mA modulation during the cardiac cycle and new prospective gating techniques like ECG pulsing protocols and whole-organ scanning offer prospects of significant extra reductions. Another way would be to use MRA when available in order to avoid all ionizing radiation. Read more .
CT technology has evolved swiftly in the past 20 years and single -slice scanners are now uncommon , with non included in this study .
For DRLs to be effective and facilitate optimisation strategies, they have to relate to current practices .
Therefore, this study recommends new DRLs which are up to 42% lower than the previous DLP values and also include a number of other CT examinations which are now commonplace in CT departments . Because the previously used metric of weighted CT does index (CTDIw) has been superseded by CTDI vol .

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