不同体质量指数患者腹部CT能谱成像扫描:与常规扫描的对比研究

Body Mass Index Based GSI in Abdominal CT:Comparative Study with Conventional Scan

目的评价CT能谱成像（GSI）在不同体质量指数（BMI）患者腹部CT扫描中的图像噪声和辐射剂量,探讨其与120 k Vp常规扫描的关系。方法搜集2015年3月至2016年3月行能谱CT上腹部增强检查的患者资料。平扫采用120 k Vp固定管电压、自动管电流技术,采用滤波反投影（FBP）、30%和50%自适应统计迭代重组（ASIR）重组3组图像;增强扫描采用GSI模式扫描,根据常规120 k Vp平扫自动m As表中出现的最大m As选择与其相应的GSI参数扫描协议,并重组66 ke V门静脉期单能量图像。根据患者BMI将所有患者分为七组,A：BMI〈22 kg/m^2;B：22 kg/m^2≤BMI〈24 kg/m^2;C：24 kg/m^2≤BMI〈26 kg/m^2;D：26 kg/m^2≤BMI〈28 kg/m^2;E：28kg/m^2≤BMI〈30 kg/m2;F：30 kg/m^2≤BMI〈32 kg/m^2;G：BMI≥32 kg/m^2。记录各组患者常规平扫和GSI增强扫描两种扫描方案的CT容积剂量指数（CTDIvol）,并测量每组患者四组图像肝实质、胆囊和胸最长肌的图像噪声。采用配对t检验比较各组患者GSI扫描和常规120 k Vp扫描的图像噪声和辐射剂量。结果 GSI模式和常规模式扫描的CTDIvol在各组分别为A：（13.4±1.3）m Gy和（9.1±2.5）m Gy,B：（13.5±1.0）m Gy和（11.2±2.0）m Gy,C：（14.3±2.4）m Gy和（12.8±2.9）m Gy,D：（15.8±2.6）m Gy和（15.6±3.3）m Gy,E：（18.3±4.3）m Gy和（17.7±4.3）m Gy,F：（22.3±5.6）m Gy和（21.3±3.6）m Gy,G：（29.1±4.9）和（27.4±2.1）m Gy。在A、B和C三组,GSI模式扫描CTDIvol高于120 k Vp常规扫描（A：55.6%,B：22.9%,C：14.2%）,在D、E、F和G组差异均无统计学意义（P值均〉0.05）。66 ke V单能量图像噪声低于120 k Vp联合FBP图像,高于120 k Vp联合50%ASIR图像,与120 k Vp联合30%ASIR图像无统计学差异。结论 BMI〉26 kg/m2时,腹部CT GSI扫描与常规120 k Vp扫描辐射剂量相当;66 ke V单能量图像噪声与常规120 k Vp扫描联合30%ASIR相当,低于常规扫描FBP重组图像。

Objective To evaluate the image noise and radiation dose of gemstone spectral imaging（GSI） mode in abdominal CT based on the body mass index（BMI） compared with conventional CT scan.Methods Patients who underwent contrast-enhanced abdomen CT scans from March to July 2014 were collected.Plain scan uses 120 k Vp fixed tube voltage,automatic tube current technology,and uses filtered back projection（FBP）,30%,and 50% adaptive statistical iterative reconstruction（ASi R） to reconstruct three groups of images;enhanced scanning using GSI mode,according to routine 120 The maximum m As appearing in the k Vp automave milliamp stopwatch was selected with its corresponding GSI parameter scan protocol and a 66 ke V portal phase single energy image was reconstructed.According to the body mass index（BMI）of the patient,all patients were divided into 7 groups：A：BMI 22 kg/m^2;B：22 kg/m^2≤ BMI 24 kg/m^2;C：24 kg/m2≤ BMI 26 kg/m^2;D：26 kg/m^2≤ BMI 28 kg/m^2;E：28 kg/m^2≤ BMI 30 kg/m^2;F：30 kg/m^2≤ BMI 32 kg/m^2;G：BMI ≥ 32 kg/m^2.The volumetric CT dose index（CTDIvol） was recorded for each group of patients with conventional plain scan and GSI-enhanced scans,and the image noise of liver parenchyma,gallbladder,and thoracic longissimus was measured in four groups of images for each group of patients.The paired t-test was used to compare the image noise and radiation dose of GSI scans and conventional 120 k Vp scans in each group of patients.Results The CTDIvol（m Gy） of the GSI mode and the conventional mode scan were A：（13.4 ± 1.3） m Gy and（9.1 ± 2.5） m Gy in each group,B：（13.5± 1.0 m Gy and（11.2 ± 2.0） m Gy,C：（14.3 ± 2.4） m Gy and（12.8 ± 2.9） m Gy,D：（15.8 ± 2.6） m Gy and（15.6 ±3.3） m Gy,E：（18.3 ± 4.3） m Gy and（17.7 ± 4.3） m Gy,F：（22.3 ± 5.6） m Gy and（21.3 ± 3.6） m Gy,G：（29.1 ± 4.9）m Gy and（27.4 ± 2.1） m Gy.In group A,B,and C,GSI scan CTDIvol was higher than 120 k Vp routine scan（A：55.6%,B：22.9%,C：14.2%）,and there was no statistical difference in D,E,F,and G groups.Significance（all P〈0.05）.The66 ke V single-energy image noise was lower than 120 k Vp combined with FBP images,and higher than 120 k Vp combined with 50% ASi R images.There was no significant difference between 120 k Vp and 30% ASi R images.Conclusion When the BMI is greater than 26 kg/m2,the abdomen CT spectral scan is comparable to the conventional 120 k Vp radiation dose;the 66 ke V single-energy image noise is equivalent to the conventional 120 k Vp scan combined with 30% ASi R,which is lower than the conventional scan FBP reconstruction image.