Application Value of Variable Exposure Conditions in One-stop Cerebral Computed Tomography Imaging
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摘要:
目的：通过比较固定曝光条件和可变曝光条件在一站式颅脑CT扫描中的影像质量和辐射剂量，探讨可变曝光条件在一站式颅脑CT扫描中的应用价值。方法：前瞻性选取我院2024年3至2024年5月间，因脑血管疾病需行头颅一站式CT扫描的患者100例，随机分为A组和B组，每组各50例。所有患者均从对比剂注射后5 s开始第1期扫描，至65 s结束，共进行18期扫描。A组患者所有扫描期相均使用相同的曝光条件，即管电压100 kV，管电流量100 mAs。B组根据各期相影像数据的诊断目的不同，使用不同的管电流量进行扫描。使用CT后处理工作站，测量平扫期大脑半球灰质、白质及颅外空气的CT值和噪声，计算图像的对比噪声比（CNR）；测量CTA图像的颅内动脉、脑实质区的CT值和噪声，计算CNR；测量CTP图像的CBV、CBF、MTT、TTP及Tmax＞6 s的脑组织体积等灌注参数，并对各期图像质量进行主观评价。使用Shapiro-Wilk检验客观指标的正态性，两组间客观指标比较采用独立样本t检验进行。采用Wilcoxon符号秩检验比较主观评分结果。结果：B组平扫图像的CNRp和主观评分优于A组。CTA图像噪声小于A组，CNRa及主观评分均高于A组；B组CTP各灌注参数与A组无差异；B组患者的DLP较A组增加约0.65%。结论：与固定曝光条件组相比，可变曝光条件一站式颅脑CT的平扫和CTA图像质量均明显提高，各灌注参数无明显差异，总体辐射剂量无明显增加的情况下，提供比固定曝光条件更好的图像质量。
Abstract:Objective: To compare the imaging quality and radiation dose under fixed and variable exposure conditions and to determine the value of variable exposure conditions in a one-stop cranial computed tomography (CT). Methods: One hundred patients who required one-stop head CT scanning because of cerebrovascular disease at our hospital between March and May 2024 were prospectively selected and randomly divided into groups A and B, with 50 patients in each group. All patients underwent the first phase of scanning at 5~65s after contrast injection, and a total of 18 scanning phases were performed. In group A, all patients underwent the same exposure conditions for all scan phases, with a tube voltage of 100 kV and tube current of 100 mAs. In group B, the patients were scanned with different tube currents according to the different diagnostic purposes of each phase of the image data. The CT values and noise of the gray matter, white matter, and extra-cranial air in the cerebral hemisphere during normal scans were measured using CT post-processing workstation, and the contrast noise ratio (CNR) of the images was calculated. The CT values and noise in the intracranial artery and parenchyma were measured using computed tomography angiography (CTA) images, and the CNR was calculated. Perfusion parameters such as cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and time to peak (TTP) in the computer-to-plate-performed image were measured, and a five-point scale was used to subjectively evaluate the image quality at each stage. The Shapiro–Wilk test was performed to test the normality of objective indicators, and an independent sample t-test was used to compare objective indicators between the two groups. The Wilcoxon signed-rank test was used to compare subjective scores. Results: The CNRp and subjective scores of the plain scan images in group B were better than those in group A. The CTA image noise in group B was lower than that in group A, and the CNRa and subjective score in group B was higher than that in group A. However, the perfusion parameters of CTP in group B did not differ significantly from those in group A. The dose length product (DLP) in group B was increased by approximately 0.65% compared with that in group A. Conclusion: Compared with the fixed exposure condition group, the image quality of the one-stop cranial CT under variable exposure conditions was significantly improved. No significant differences were observed in any perfusion parameter, and the overall radiation dose was not significantly increased, providing better image quality than that under fixed exposure conditions.
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图 1 两种扫描协议示意图
注：（a）A组扫描使用固定曝光条件，管电流量100 mAs；（b）B组根据不同扫描期相使用可变曝光条件，平扫期（第1期）管电流量240 mAs，CTA期（第4~7期）管电流量150 mAs，其余期相管电流量75 mAs。
Figure 1. Schematic diagram of the two scanning protocols
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图 2 A组平扫和CTA图像
注：（a）（b）为A组1例患者，各期管电流量均使用100 mAs进行扫描，平扫图像灰白质对比尚可，噪声稍大，右侧尾状核头低密度区显示欠清晰，诊断信心不足（白箭）。CTA图像上分支血管边缘欠光整，显示欠清晰（白箭）。
Figure 2. Non-contrast and CTA images of one patient in group A
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图 3 B组平扫和CTA图像
注：（a）（b）为B组1例患者，平扫期使用240 mAs进行扫描，图像细腻，灰白质对比良好。CTA期使用150 mAs进行扫描，血管边缘光整，分支血管显示清晰。
Figure 3. Non-contrast and CTA images of one patient in group B
表 1 两组患者一般资料及辐射剂量比较
Table 1 General information and radiation dose comparison of the two patient groups
项目 组别 统计检验 A组 B组 统计值 P 例数 50 50 − − 性别 男 28 27 0.400a 0.841 女 22 23 评价年龄/岁 62.8±13.5 60.3±12.1 0.997 0.321 身高/m 1.66±0.07 1.65±0.06 0.899 0.371 体质量/kg 68.5±9.1 69.8±8.9 0.773 0.441 扫描长度/cm 140.40±2.83 140.80±3.96 − 0.581 0.562 CTDIvol /mGy 152.20±0.15 153.09±0.412 −14.232 ＜0.001 DLP/（mGy·cm） 2136.74 ±39.822156.52 ±57.05−2.010 0.047 注：CTDI为CT剂量指数；DLP为剂量长度乘积，a为$\chi^2 $值，其他为t值。 
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表 2 两组患者平扫图像质量比较
Table 2 Comparison of plain scan image quality between the two patient groups
项目 组别 统计检验 A组 B组 统计值 P 灰质CT值 36.41±1.51 36.15±1.26 0.896 0.370 白质CT值 27.14±1.69 26.85±1.54 0.831 0.408 图像噪声SDp 4.75±0.78 1.92±0.22 8.537 0.000 背景噪声SD1 3.19±0.55 1.70±0.28 16.826 0.000 CNRp 10.33±2.11 20.72±3.53 −8.473 0.000 评分 3（3，3） 5（4，5） −8.681a 0.000 注：a为Z值，其余统计值均为t值。
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表 3 两组患者CTA图像质量比较
Table 3 Comparison of CTA image quality between the two patient groups
项目 组别 统计检验 A组 B组 统计值 P 颅内动脉CT值 391.64±64.57 409.61±72.56 1.113 0.269 动脉噪声SDa 7.00±0.73 5.37±0.65 −6.963 0.000 脑实质CT值 36.53±1.61 36.32±1.66 −0.546 0.586 图像噪声SD2 9.13±1.44 6.42±0.46 −7.414 0.000 CNRa 39.53±8.23 58.63±12.93 8.021 0.000 评分 4（3，4） 5（5，5） 5.745a 0.000 注：a为Z值，其余统计值均为t值。
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表 4 两组患者CTP结果和图像质量比较
Table 4 Comparison of CTP results and image quality between the two patient groups
项目 组别 统计检验 A组 B组 统计值 P 尾状核头 CBV 3.54±0.96 3.63±1.16 − 0.010 0.992 CBF 99.22±40.91 107.25±53.37 0.283 0.777 MTT 3.94±1.53 3.79±1.58 − 0.430 0.668 TTP 19.13±2.79 18.31±2.41 −1.391 0.168 颞叶白质 CBV 1.98±0.72 2.00±0.79 − 0.152 0.880 CBF 45.03±18.42 42.76±23.26 −1.131 0.258 MTT 5.55±2.30 5.59±2.07 0.470 0.639 TTP 20.58±2.81 20.39±2.55 − 0.316 0.753 评分 4（4，5） 4（4，5） −1.076a 0.282 Tmax＞6 s的脑组织体积/mL 74.19±126.79 34.56±78.94 1.876 0.064 注：a为Z值，其余统计值均为t值。
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