BMI指数及自动管电流调节技术降低螺旋CT腰椎扫描辐射剂量的价值

摘要

目的:探讨身体质量指数(BMI)与自动管电流调节技术(ATCM)联合应用在腰椎容积螺旋CT扫描降低辐射剂量中的价值.方法:前瞻性设计和连续收集我院进行腰椎螺旋CT检查50例,根据BMI指数分A大组(BMI≤24kg/m2)和B大组(BMI＞24kg/m2),各25人,两组内随机分为5个亚组,分别接受以下5组不同扫描参数组合进行容积CT扫描:亚组1采用固定管电流技术,405mAs,120kV;亚组2～5均采用自动管电流调节技术,噪声值分别为21Hu、25Hu、25Hu、25Hu,管电流范围分别为100～710mAs、100～710mAs、40～300mAs、40～300 mAs,管电压分别为120kV、120kV、120kV、100kV.记录随机容积CT剂量指数(CTDIvol)及剂量长度乘积(DLP).对图像进行质量评分,并测量各组腰4～5椎间盘中心水平两侧腰大肌标准差(SD)及信噪比(SNR),进行统计学分析.结果:A和B两大组的组内5小组间BMI值均相似(P＜0.001).A大组1～5亚组CTDIvol值、DLP值存在统计学差异(P＜0.001),第5组CTDIvol值、DLP值分别为第1组的37.46％、38.59％；主观图像质量评分在5个亚组间无统计学差异；腰大肌SD值在各亚组间存在统计学差异,信噪比在各亚组无统计学差异.B大组内1～5小组CTDI vol值、DLP值存在统计学差异(P＜0.01),第4组、第5组CTDIvol值分别为第1组的67.11％、42.60％,DLP值分别为第1组的65.07％、40.93％;主观图像质量评分、腰大肌SD值、信噪比存在统计学差异.结论:BMI指数的应用有助于更好地利用自动管电流调节技术降低辐射剂量,而不引起的图像质量的降低.BMI≤24kg/m2受试者可采用亚组5参数进行扫描,BMI＞24kg/m2受检者应采用亚组4参数进行扫描.%Purpose: To explore the value of body mass index (BMI) and automatic tube current modulation (ATCM) in lowering radiation dose for patients performing lumbar spine volume CT examinations. Methods: Fifty patients who underwent spiral CT exam were prospectively collected. According to their BMI, they were divided into 2 groups: BMK24kg/m2 in group A, BMI>24kg/m2 in group B. Each group was divided into 5 subgroups who received CT scan with following different parameters. Subgroup 1 received CT scan with fixed tube current 405 mAs and tube voltage 120 kV. Subgroup 2, subgroup 3, subgroup 4, subgroup 5 were examined with Smart mA, whose noise index(NI) was respectively 21Hu, 25Hu, 25Hu, 25 Hu, range of tube current was automatically selected in 100-710 mAs, 100-710 mAs, 400-300 mAs, 40-300 mAs, and tube voltage was 120kV, 120kV, 120 kV, 100 kV respectively. The CT dose index of volume (CTDIvol) and the doses length product (DLP) were recorded. VR and batch reconstruction imaging were evaluated by the image quality score (IQS). The image standard deviation (SD) and signal noise ratio of psoas major were measured at the middle level of L4-5 lumbar dise in all groups. The statistical analysis was performed. Results: There was no statistical significant different (P>0.001) between BMI in group A and B. The CTDIvol and DLP of different subgroups displayed statistical difference (P<0.001). The CTDIvol and DLP in subgroup 5 was 37.46% and 38.59% of subgroup 1. There was no statistical difference among 5 subgroups in IQS of VR and batch imaging. There was statistical difference in SD of psoas major. The SNR of psoas major showed with no difference among subgroups. In group B, the CTDIvol and DLP of different subgroups existed statistical difference (P<0.01). The CTDIvol of subgroup 4 and subgroup 5 was 67.11%, 42.60% of subgroup 1. The DLP of subgroup 4 and subgroup 5 was 65.07%, 40.93% of subgroup 1 retrospectively. IQS of VR and batch imaging showed statistical difference. There was a statistical difference in SD and SNR of psoas major. Conclusion: It is BMI that helps better utilizing ATCM to lower radiation dose with no lose of image quality. People whose BMI is less than 24kg/m2 may be scanned with the parameters of subgroup 5. People whose BMI is more than 24kg/m2 may be scanned with the parameters of subgroup 4.