Radiation dose and image quality in intraoperative CT (iCT) angiography of the brain with stereotactic head frames

ObjectivesIntraoperative CT (iCT) angiography of the brain with stereotactic frames is an integral part of navigated neurosurgery. Validated data regarding radiation dose and image quality in these special examinations are not available. We therefore investigated two iCT protocols in this IRB-approved study.MethodsRetrospective analysis of patients, who received a cerebral stereotactic iCT angiography on a 128 slice CT scanner between February 2016 and December 2017. In group A, automated tube current modulation (ATCM; reference value 410mAs) and automated tube voltage selection (reference value 120kV) were enabled, and only examinations with a selected voltage of 120kV were included. In group B, fixed parameters were applied (300mAs, 120kV). Radiation dose was measured by assessing the volumetric CT dose index (CTDIvol), dose length product (DLP) and effective dose (ED). Signal-to-noise ratio (SNR) and image noise were assessed for objective image quality, visibility of arteries and grey-white differentiation for subjective image quality.ResultsTwo hundred patients (n=100 in each group) were included. In group A, median selected tube current was 643mAs (group B, 300mAs; p<0.001). Median values of CTDIvol, DLP and ED were 91.54mGy, 1561mGycm and 2.97mSv in group A, and 43.15mGy, 769mGycm and 1.46mSv in group B (p<0.001). Image quality did not significantly differ between groups (p>0.05).ConclusionsATCM yielded disproportionally high radiation dose due to substantial tube current increase at the frame level, while image quality did not improve. Thus, ATCM should preferentially be disabled.Key Points center dot Automated tube current modulation (ATCM) yields disproportionally high radiation dose in intraoperative CT angiography of the brain with stereotactic head frames.center dot ATCM does not improve overall image quality in these special examinations.center dot ATCM is not yet optimised for CT angiography of the brain with major extracorporeal foreign materials within the scan range.