自动毫安低剂量CT扫描对结肠病变的显示及其对图像质量的影响

目的 评估自动毫安低剂量CT扫描对结肠病变的图像质量及对辐射剂量的影响.方法 预实验采用猪结肠制备息肉模型,通过改变噪声指数(NI)调节毫安,对图像质量进行评价,得出可应用于临床病例组的NI值.病例组采用前瞻性研究的方法,搜集连续71例临床怀疑为结肠病变的患者,71例在CT扫描前均已行结肠镜检查.将第1组39例(2007年1月至2007年6月检查的患者)按照数字表法随机分为A、B、C 3个亚组,N1分别取10(15例)、13(13例)和16(11例),NI不随扫描体位而改变;第2组32例(2007年7月至2008年1月检杏的患者)NI随扫描体位而改变,NI分别取10(俯卧位)和20(仰卧位).以相同方法进行扫描获取横断面图像、CT虚拟结肠镜(CTVC)及透亮法显示(Raysum)的重组图像并进行图像质量评分.阳性病例均经肠镜活检或手术病理证实.将第1组中A、B、C 3个亚组间以及第2组中不同扫描体位所得平均CT剂量加权指数(CTDIw)与标准值(26.92 mGy)进行比较,第1组病例亚组间的图像评分以及第2组病例不同扫描体位的图像评分均采用等级资料的秩和检验进行比较.结果 第1组:NI=10时,横断面和重组图像平均评分分别为4.2和2.4分,平均CTDIw为17.51 mGy;NI=13时,上述平均评分分别为3.2和2.5分,平均CTDIw为12.90 mGy;NI=16时,上述平均评分分别为2.9和2.7分,平均CTDIw为5.94 mGy.当NI提高时,横断面图像质量评分降低,差异有统计学意义(H=20.01,P＜0.01);对于重组图像,图像质量评分不随NI加大而改变,差异无统计学意义(H=0.81,P＞0.05).第2组:NI=10时,横断面图像和重组图像的平均评分分别为3.6和2.3分;NI=20时,上述平均评分分别为2.2和2.3分,平均CTDIw为11.63 mGy.当NI由10提高到20时,横断面图像质量评分降低,差异有统计学意义(H=20.84,P＜0.01);重组图像评分不随NI的增加而降低(H=0.29,P＞0.05).第1组中NI分别为10、13和16时,CTDIw平均降低了35.O%、52.1%和77.9%;第2组中CTDIw平均降低了56.8%.结论 自动毫安低剂量CT扫描技术可以在明显降低辐射剂量的同时,兼顾图像质量.

The impact of auto-mA low-dose colonic CT scanning on image quality and lesion visualization

Objective To evaluate the effect of low-dose colonic CT scanning in image quality and lesion revealing with different noise idex.Methods Model group:in order to find the optimal scanning parameter range,small simulated polyps in pig colon was prepared and mA was modulated by regulating noise index.Images were reprocessed with CT colonography and Raysum reconstructions.Image quality and the lesion revealing situation were evaluated and scored based on both reconstructive and axial images.The study of patient group was prospective and continuous.All positive cases were comfirmed by biopsy or surgery pathology.Two groups of patients were enrolled.First group(39 cases from January 2007 to June 2007):patients were divided into three sub-groups randomly(15 cages with NI=10,13 cases with NI:13,11 cases with NI=16),while NI was not changed with position.Second group(32 cases from Jury 2007 to January 2008):patients were scanned and NI was changed with different position(NI=10,20).The average X-ray radiation values of two patient groups were compared with standard values.All data were processed with rank sum tesL Results First group:when NI=10,the average scores of axial and constructive images were 4.2 and 2.4 respectively,when NI=13,those were 3.2 and 2.5 respectively,When NI=16.those were 2.9 and 2.7 respectively.and the average CTDlw were 17.51,12.90 and 5.94 mGy respectively.When NI increased,the average scores of axial decreased(H=20.01,P＜0.01),the average scores of constructive images did not changed(H=0.81,P＞0.05).Second group:when NI=10,the average scores of axial and constructive images were respectively 3.6 and 2.3,when NI=20,those were 2.2 and 2.3 respectively,and the average CTDIw was 11.63 mGy.When NI increased from 10 to 20,the average scores of axial decreased(H=20.84,P＜0.01),the average scores of constructive images did not decreased(H=0.29,P＞0.05).In the first group,the average CTDIw wag reduced by 35.0%,52.1%and 77.9%respectively when NI was 10,13 and 16.In the second group,the average CTDIw Was reduced by 56.8%.Conclusions Auto-mA low-dose CT scanning could reduce X-ray radiation obviously,while not affecting image quality.