In three-dimensional computed tomography angiography (3D-CTA) in our facility, we usually scan\nthe volume of the brain according to the bolus tracking method. Fluoroscopic slice is placed at the\nWillis�s ring and the timing of scan is determined subjectively by a radiological technologist after\nstrong enhancement of the basal cerebral artery is confirmed. In these procedures, however, variation\nof scan timing is often problematic. Therefore, we design the surpassing method to place the\nsmall region-of-interest (ROI) at the basal cerebral arteries and to start CT scan automatically. In\nthis protocol, the fluoroscopic slices of the distal internal carotid arteries are selected referring to\nthe precontrast volume data, small ROIs are set in bilateral internal carotid arteries, and scan\ntrigger of CT is started automatically at the threshold of 170 HU. The maximum 80 mL of iodine\ncontrast agent 300 mgI/mL is injected intravenously at the rate of 4.0 mL/sec, and the volume of\nthe arterial phase is scanned automatically. We measure ROIs at the internal carotid arteries\nbased on the obtained volume data of arterial phase and estimate the optimal scan timings from\nthe fluoroscopic CT images reformatted at the intervals of 0.1 sec. In 38 of 53 patients, placement\nof the small ROIs is succeeded and automatic or manual CT scan is performed. In the patients who\nsucceed in placement of the small ROIs, optimal scan timing of the arterial phase is obtained, while\nin the patients who fail placement of the small ROIs, a large variation is observed in their scan\ntimings. Their results suggest that more stable scanning of the arterial phase is available by means\nof small ROI placement and automatic scanning. The clinical significance is large because the stability\nand reproducibility of the examination provide a quantitative analysis and more accurate\ndiagnosis.
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