“三低”技术联合全模型迭代重建算法在头颈部CT血管成像中的可行性研究

A feasibility study on ＂ Tri-Low＂ technology in combination with iterative model reconstruction （IMR） algorithm in CT angiography （CTA） of the head-and-neck vessels

目的探讨80kV低管电压、低对比剂注射速率和低对比剂用量的“三低”技术，联合全模型迭代重建（IMR）算法在头颈部CT血管成像（CTA）检查的可行性。方法前瞻性连续收集2015年7—11月行头颈部CTA检查的患者60例，采用随机数字表法将其分为A、B两组，每组各30例。A组为常规剂量组，管电压120kV，滤过反投影（FBP）重建，对比剂注射速率4．5～5．5ml／s，注射时间10S；B组为80kV低管电压组，分别使用FBP和IMR进行图像重建，得到B1和B2两组图像，对比剂注射速率3．5～4．0ml／s，注射时间10s。测量并计算A组、B1组、B2组的图像动脉血管CT值、图像噪声、信噪比（SNR）和对比噪声比（CNR），并由2名放射诊断医师对图像质量按照5分法进行评价。3组图像间动脉血管CT值、图像噪声、SNR和CNR采用单因素方差分析，图像质量主观评价采用Kruskal-Wallis检验，两组检查的容积CT剂量指数（CTDIvol）和剂量长度乘积（DLP）比较采用两个独立样本t检验。结果A、B1和B2组3组图像质量主观评分范围分别为3～5分、2～4分和3～5分，B1组有12例患者图像之间评分≤2分，图像无法诊断。A和B1、A和B2、B1和B2图像之间评分差异均有统计学意义（t=4．55、-6．58、-2．03，P〈0．05）。B2组与A组的图像客观指标SNR和CNR比较差异无统计学意义（P〉0．05），但B2和A组图像的SNR、CNR均优于B1组，差异均有统计学意义（t=-12．14、13．39、-9．96、9．45，P〈0．05）。B组CTDIvol[（1．7±0．2）mGy]比A组[（8．9±1．0）mGy]减少了80．9％，DLP[（77．9±9．0）mGy·cm]比A组[（415．5±56．7）mGy·cm]减少了81．3％，B组对比剂注射速率[（3．9±0．1）ml／s]比A组[（5．0±0．2）ml／s]减少了22．0％，B组对比剂总量[（39．2±1．9）m1]比A组[（50．3±2．2）ml]减少22．1％，差异有统计学意义（t=39．1、32．2、20．8、20．8，P〈0．05）。结论使用80kV管电压、低对比剂注射速率和用量，并使用IMR算法进行图像重建，进行头颈部CTA扫描是可行的。可以在保证图像质量的基础上，使患者辐射剂量减少81．3％。

Objective To evaluate the feasibility of low-tube-voltage, low injection rate, low contrast agent dosage in combination with iterative model reconstruction（IMR） algorithm in CT angiography （CTA） of the head-and-neck vessels. Methods Sixty patients who underwent CT angiography of the head-and-neck vessels were randomly divided into groups A and B with 30 cases in each group. Patients in group A received a conventional scan with 120 kVp and fiherbaek projected（FBP） reconstruction. Patients in group B received a low-dose scan with 80 kVp, and image reconstruction with FBP（ group B1 ） and IMR （group B2）algorithm. The contrast agent protocol were as follows： the injection time in all patients was 10s, the injection rate was 4.5 -5.5 ml/s in group A while 3.5 -4.0 ml/s in group B. The CT values of artery, image noise, signal to noise ratio（SNR） and contrast to noise ratio （CNR） were measured and compared among three groups with One-way ANOVA analysis. Image quality was evaluated by two radiologists with five scale method, and compared with Kruskal-Wallis test. The CT dose index volume （CTDIvol） and dose length product （DLP） were recorded and compared between groups with two independent samples t-test. Results The image quality scores of groups A, Bland B2 were 3 -5, 2 -4 and 3 - 5, respectively . hnage quality of twelve patients in group BI couldn＇t meet the diagnostic requirements but none in group A and B2. The objective image parameters SNR and CNR for group B2 were equal to group A（P 〉0.05）, while those for group B1 were lower than group A （t=13.39, 9.45, P 〈0.05） and group B2 （t = -12. 14, -9.96,P 〈0.05）. CTDIvol and DLP for group B were separately 80.9% , 81.3% lower than those of group A（t = 39. 1, 32.2,P 〈0.05）. The injection rate and contrast agent volume for group B were separately 22.0% , 22. 1% lower than those of group A（t = 20.8, 20.8, P 〈 0. 01 ）. Conclusions It is feasible in CT angiography of the head-and-neck vessels with lower tubevoltage, lower injection rate, lower contrast agent dose and combining with iterative model reconstruction algorithm. This protocol can reduce the radiation dose by 81.3% while maintaining image quality. Trial registration Chinese clinical trial registry,ChiCTR-BOC-16010060