Department of Medical Physics, University Hospital of Heraklion, Crete, Greece.
Invest Radiol. 2013 Apr;48(4):192-9. doi: 10.1097/RLI.0b013e31827efc17.
The aim of the present phantom study was to investigate the effect of x-ray tube parameters and iodine concentration on image quality and radiation dose in cerebral computed tomographic (CT) angiographic examinations of pediatric and adult individuals.
Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old children and the RANDO phantom that simulates the average adult individual were used. Cylindrical vessels were bored along the brain-equivalent plugs of each physical phantom. To simulate the brain vasculature, vessels of 0.6, 1, 2, and 3 mm in diameter were created. These vessels were filled with contrast medium (CM) solutions at different iodine concentrations, that is, 5.6, 4.2, 2.7, and 1.4 mg I/mL. The phantom heads were scanned at 120, 100, and 80 kV. The applied quality reference tube current-time product values ranged from a minimum of 45 to a maximum of 680. The CT acquisitions were performed on a 16-slice CT scanner using the automatic exposure control system. Image quality was evaluated on the basis of image noise and contrast-to-noise ratio (CNR) between the contrast-enhanced iodinated vessels and the unenhanced regions of interest. Dose reduction was calculated as the percentage difference of the CT dose index value at the quality reference tube current-time product and the CT dose index at the mean modulated tube current-time product.
Image noise that was measured using the preset tube current-time product settings varied significantly among the different phantoms (P < 0.0001). Hounsfield unit number of iodinated vessels was linearly related to CM concentration (r² = 0.907) and vessel diameter (r² = 0.918). The Hounsfield unit number of iodinated vessels followed a decreasing trend from the neonate phantom to the adult phantom at all kilovoltage settings. For the same image noise level, a CNR improvement of up to 69% and a dose reduction of up to 61% may be achieved when CT acquisition is performed at 80 kV compared with 120 kV. For the same CNR, a reduction by 25% of the administered CM concentration may be achieved when CT acquisition is performed at 80 kV compared with 120 kV.
In cerebral CT angiographic studies, appropriate adjustment of the preset tube current-time product settings is required to achieve the same image noise level among participants of different age. Cerebral CT angiography at 80 kV significantly improves CNR and significantly reduces radiation dose. Moreover, at 80 kV, a considerable reduction of the administered amount of the CM may be reached, thus reducing potential risks for contrast-induced nephropathy.
本体模研究旨在探讨 X 射线管参数和碘浓度对儿科和成人颅脑 CT 血管造影检查中图像质量和辐射剂量的影响。
使用代表新生儿、1 岁、5 岁和 10 岁儿童以及模拟成年个体的 RANDO 体模的 4 个体模。在每个物理体模的大脑等效插件上钻有圆柱形血管。为了模拟脑血管，创建了直径为 0.6、1、2 和 3 毫米的血管。这些血管用不同碘浓度的对比剂（CM）溶液填充，即 5.6、4.2、2.7 和 1.4 mg I/mL。用 120、100 和 80 kV 扫描体模头部。应用的质量参考管电流-时间乘积值范围从最低 45 到最高 680。CT 采集在 16 层 CT 扫描仪上使用自动曝光控制系统进行。根据对比增强碘血管与未增强感兴趣区之间的图像噪声和对比噪声比（CNR）评估图像质量。剂量减少被计算为质量参考管电流-时间乘积的 CT 剂量指数值与平均调制管电流-时间乘积的 CT 剂量指数值的百分比差异。
使用预设管电流-时间乘积设置测量的图像噪声在不同体模之间差异显著（P<0.0001）。碘化血管的亨氏单位数与 CM 浓度呈线性相关（r²=0.907）和血管直径（r²=0.918）。在所有千伏设置下，碘化血管的亨氏单位数从新生儿体模到成年体模呈下降趋势。在相同的图像噪声水平下，与 120 kV 相比，80 kV 时 CT 采集可实现高达 69%的 CNR 提高和高达 61%的剂量减少。对于相同的 CNR，与 120 kV 相比，80 kV 时 CT 采集可将给药 CM 浓度降低 25%。
在脑 CT 血管造影研究中，需要适当调整预设管电流-时间乘积设置，以在不同年龄的参与者之间达到相同的图像噪声水平。80 kV 脑 CT 血管造影显著提高 CNR 并显著降低辐射剂量。此外，在 80 kV 时，可以达到 CM 给药量的可观减少，从而降低对比剂肾病的潜在风险。
