The number of CTA examinations is continually increasing compared with DSA examinations, because of the development of multisection CTA techniques. The effective dose is a useful tool for comparison of radiation exposure of different imaging techniques. The radiation exposure must be kept as low as reasonably achievable (ALARA principle) for the avoidance of radiation-related risks. The challenge is that CTA and DSA have very different irradiation geometries and the radiation exposure is reported in different quantities. Also, the new conversion factors from the dose-area product (DAP) of DSA and the dose-length product (DLP) of CTA to effective dose are missing. Consequently, the comparison of the radiation exposures is difficult. The solution is to determine the effective doses and the conversion factors with new tissue weighting factors according to ICRP 103 guidelines using the same dose determination technique for both CTA and DSA for an objective comparison.

Knowledge of the radiation exposures and details of each imaging technique will help to optimize the imaging procedures. The conversion factors we determined are a useful tool for clinicians and radiologists to estimate the effective doses of both imaging techniques and to compare the radiation exposure.

In the future, the radiation exposure of new imaging techniques such as dual-energy head and neck CTA and flat-panel DSA should be determined.

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