Circle of Willis at CT Angiography: Dose Reduction and Image Quality—Reducing Tube Voltage and Increasing Tube Current Settings

Purpose: To prospectively assess the effects of lower tube voltage and various effective tube currents on image quality for computed tomographic (CT) angiography of the circle of Willis. Materials and Methods: Institutional review board approval was obtained. Patients or family provided written informed consent. Signal-to-noise ratios (SNRs) were determined in a head phantom for various effective tube currents with tube voltages of 90, 120, and 140 kVp. Patients were referred for CT angiography because of acute subarachnoid hemorrhage (n = 20) or family history of cerebral aneurysms (n = 20). In each group, 10 patients were scanned with 120 kVp and 200 mAseff and 10 were scanned with 90 kVp and 330 mAseff (CT dose index volumes, 27.2 mGy and 20.6 mGy, respectively). CT numbers were measured in the internal carotid artery at the T junction and compared with a t test. Two radiologists used a five-point scale to subjectively score arterial enhancement, depiction of small arterial detail, image noise, venous ...