Waaijer Annet, Prokop Mathias, Velthuis Birgitta K, Bakker Chris J G, de Kort Gerard A P, van Leeuwen Maarten S
Department of Radiology, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, the Netherlands.
Radiology. 2007 Mar;242(3):832-9. doi: 10.1148/radiol.2423051191. Epub 2007 Jan 17.
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.
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 mAs(eff) and 10 were scanned with 90 kVp and 330 mAs(eff) (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 contamination, and interference of subarachnoid blood. Mann-Whitney U test was used for statistical analysis.
In the phantom, SNR(2) was proportional to effective tube current and CT dose index volume. With an identical effective tube current, SNR(2) was lower at 90 kVp than at 120 or 140 kVp. With identical CT dose index volume, tube voltage of 90 kVp resulted in a 45%-52% increase of SNR(2) compared with SNR(2) at 120 kVp. In patients, mean attenuation in the internal carotid artery T junction was higher with 90 kVp (340 HU) than with 120 kVp (252 HU, P < .001). Although dose at 90 kVp was 30% lower than dose at 120 kVp, scores for arterial enhancement and depiction of small arterial detail were higher at 90 kVp than at 120 kVp (4.0 vs 3.2 and 3.6 vs 3.1, respectively; P < .005).
In head phantoms, lower tube voltage improved SNR at equal radiation doses. For CT angiography of the circle of Willis, this translated into superior image quality at 90 kVp.
前瞻性评估较低管电压和不同有效管电流对 Willis 环计算机断层扫描（CT）血管造影图像质量的影响。
获得机构审查委员会批准。患者或家属提供书面知情同意书。在头部模型中，针对管电压为 90、120 和 140 kVp 的不同有效管电流测定信噪比（SNR）。因急性蛛网膜下腔出血（n = 20）或有脑动脉瘤家族史（n = 20）而被转诊进行 CT 血管造影的患者。每组中，10 例患者采用 120 kVp 和 200 mAs（有效）进行扫描，10 例患者采用 90 kVp 和 330 mAs（有效）进行扫描（CT 剂量指数容积分别为 27.2 mGy 和 20.6 mGy）。在颈内动脉 T 交界处测量 CT 值，并采用 t 检验进行比较。两名放射科医生使用五点量表对动脉强化、小动脉细节显示、图像噪声、静脉污染和蛛网膜下腔血液干扰进行主观评分。采用 Mann-Whitney U 检验进行统计分析。
在模型中，SNR(2)与有效管电流和 CT 剂量指数容积成正比。在相同有效管电流下，90 kVp 时的 SNR(2)低于 120 或 140 kVp 时。在相同 CT 剂量指数容积下，与 120 kVp 时的 SNR(2)相比，90 kVp 的管电压使 SNR(2)增加了 45% - 52%。在患者中，90 kVp 时颈内动脉 T 交界处的平均衰减（340 HU）高于 120 kVp 时（252 HU，P <.001）。尽管 90 kVp 时的剂量比 120 kVp 时低 30%，但 90 kVp 时动脉强化和小动脉细节显示的评分高于 120 kVp 时（分别为 4.0 对 3.2 和 3.6 对 3.1；P <.005）。
在头部模型中，较低管电压在同等辐射剂量下提高了 SNR。对于 Willis 环的 CT 血管造影，这意味着在 90 kVp 时图像质量更佳。
