Abstract
Xenon CT CBF examination has much radiation exposure because of frequent scanning of the same slice. First, we did questionnaire investigation in Japanese 202 institutions in three months since December, 2004. The questionnaire result showed that the number of scan slices was 2.6±1.3 (mean±SD). The number of scans per one slice was 9.3±1.7. The x-ray tube voltage was 120 kV in most institutions. The x-ray tube current was 347±128 mAs. We got an answer from a 54 institution about CTDIw value. The radiation exposure in these institutions was 1, 108.3+/-874.4 mGy·cm.
Second, we studied the influence that decrease of scan frequency gave to radiation exposure and cerebral blood flow value. In a 4 slices scan with a CT device of CTDIw 39.6 mGy, radiation exposure decreased by 634 mGy when we changed scan frequency from seven times to three times. The decrease of scan frequency resulted in cerebral blood flow increase of 3-5ml/100mg/min. In conclusion, among Japanese institutions, number of scan slices and scan frequency per one slice were various. Making of a guideline and reconsideration of the scan conditions are necessary for reduction of radiation exposure.
