能谱智能匹配联合双低技术在CT门静脉成像中的可行性研究

目的 探索单能量成像结合自适应统计迭代重建（adaptive statistical iterative reconstruction，ASIR）及自动能谱协议选择（automatic spectral imaging mode selection，ASIS）技术在个体化降低患者门静脉造影辐射剂量、对比剂剂量中的应用价值。方法 回顾性收集华中科技大学同济医学院附属协和医院2017年1月至2017年4月120例临床需进行上腹部增强检查的受检者资料（男80例，女40例），按扫描方案分为3组，每组各40例。A组采用常规120 kVp扫描，噪声指数（NI）=10，对比剂用量为450 mgI/kg，图像采用50% ASIR重建；B、C两组采用能谱成像模式，NI=10（B组），NI=13（C组），对比剂用量均为300 mgI/kg，图像采用60 keV+50% ASIR重建。采用单因素方差分析比较3组图像中门静脉、肝实质的平均CT值及其差值、图像噪声、信噪比（SNR）及对比噪声比（CNR）。由两位高年资放射科医师对3组图像进行主观图像质量评分。记录患者的容积CT剂量指数（CTDI_vol）、剂量长度乘积（DLP）并计算有效剂量（E）。结果 B、C两组对比剂用量较A组降低了约30%。A、B、C组图像的门静脉CT值分别为168.22±17.82、209.06±20.07、211.03±25.60，B、C组与A比较，差异有统计学意义（t=-9.625、-8.680，P<0.05）。A、B、C 3组门静脉与肝实质CT差值分别为60.01±17.01、106.63±25.83、107.72±25.39，B、C组与A组比较，差异有统计学意义（t=-9.536、-9.857，P<0.05）。SNR分别为8.48±1.41、12.64±2.94、10.77±1.94，CNR分别为5.16±1.80、8.13±2.54、7.32±1.84，图像质量评分分别为（3.53±0.68）、（4.75±0.54）和（4.53±0.64）分，B、C组的SNR、CNR和图像质量评分与A组比较，差异有统计学意义（t=-8.082、-6.064、-6.050、-5.308、-8.912、-6.779，P<0.05）。A、B、C组CTDI_vol分别为（12.15±5.02）、（12.34±4.18）、（10.03±3.13）mGy，DLP分别为（348.62±155.99）、（355.56±131.07）、（287.10±92.25）mGy·cm，E分别为（5.23±2.34）、（5.33±1.97）、（4.31±1.38）mSv，相对于A、B两组，C组的CTDI_vol、DLP和E差异均有统计学意义（t=2.274、2.147、2.147、2.812、2.702、2.702，P<0.05），分别降低了19%。结论 CT门静脉成像时，选择NI=13，60 keV结合50%ASIR重建及ASIS技术可以个体化降低患者的对比剂剂量和辐射剂量，并提供满足诊断要求的图像。

Feasibility study of automatic spectral imaging protocol selection combined with double low technique in CT portal vein imaging

Objective To explore the application value of virtual monochromatic imaging combined with adaptive statistical iterative reconstruction (ASIR) and automatic spectral imageing mode selection(ASIS) in reducing the radiation dose and contrast dose of CT portal venography.Methods We retrospectively collected 120 cases (80 males and 40 females) who underwent upper abdominal enhancement CT from January 2017 to April 2017. Patients were divided into 3 groups (40 cases in each group) according to the scanning program. Group A used conventional 120 kVp scan, NI=10, contrast agent dosage was 450 mgI/kg of body weight, image was reconstructed with 50% ASIR technique; Groups B and C used spectral CT mode, NI=10 (Group B), NI=13 (Group C), the amount of contrast agent was 300 mgI/kg of body weight, and the image was reconstructed with 60 keV+50% ASIR. One-way analysis of variance was used to compare the mean CT values and their differences, image noise, SNR and CNR of portal vein and liver parenchyma in three groups of images. Subjective image quality scores were performed on three groups of images by two senior radiologists. The patient''s CTDI_vol, DLP were recorded and the E was calculated.Results The amount of contrast agent in group B and C was reduced by about 30% compared with group A. The portal vein CT values of groups A, B, and C were 168.22±17.82, 209.06±20.07, and 211.03±25.60. The portal vein CT values of group B and C were significantly higher than those of group A,respectively(t=-9.625, -8.680, P<0.05). The CT value difference between portal vein and liver parenchyma was 60.01±17.01, 106.63±25.83, 107.72±25.39, respectively. SNRs were 8.48±1.41, 12.64±2.94, 10.77±1.94, and CNR were 5.16±1.80, 8.13±2.54, 7.32±1.84, respectively. The image quality scores were 3.53±0.68, 4.75±0.54 and 4.53±0.64, respectively. The CT value difference, SNR, CNR and image quality scores of group B and group C were significantly higher than those in group A(t=-9.536, -9.857, -8.082, -6.064, -6.050, -5.308, -8.912, -6.779,P<0.05). The CTDI_vol of groups A, B and C were (12.15±5.02) mGy, (12.34±4.18) mGy, (10.03±3.13) mGy, DLP were (348.62±155.99) mGy·cm, (355.56±131.07) mGy·cm, (287.10±92.25) mGy·cm, respectively, E were (5.23±2.34) mSv, (5.33±1.97) mSv, (4.31±.1.38) mSv, compared with the A and B groups, the CTDI_vol, DLP and E of the C group were significantly lower(t=2.274,2.147, 2.147,2.812,2.702, 2.702,P<0.05), and CTDI_vol, DLP and E were decreased by 19%.Conclusions In CT portal venography, NI=13, 60 keV combined with 50% ASIR reconstruction and ASIS can be used to personalize the contrast dose and radiation dose of the patient and provide images that meet the diagnostic requirements.