16层螺旋CT主动脉低剂量扫描研究

Effects of 16-multi-detector row CT aortography with lower tube current

目的研究16层螺旋CT主动脉造影低管电流扫描方案。方法研究分两步。初步研究筛选西安第四军医大学西京医院临床送检的可疑主动脉病变或动脉瘤术后随访病例（夹层动脉瘤除外）共58例患者扫描70例次。包括真性动脉瘤、假性动脉瘤、主动脉壁内血肿、主动脉粥样硬化和腔内隔绝术后随访病例。随机选取10例为常规剂量175mAs扫描，低剂量组按体重分为〈65kg，65-75kg，〉75kg3组，分别采用低管电流为25、50、75mAs，其余扫描参数同常规剂量组。记录单次加权CT剂量指数（CTDI）和平均剂量长度乘积（DLP）。对不同低剂量组的主动脉图像满足诊断率进行比较，并进行统计学处理。第2步筛选西京医院临床送检60例可疑各型夹层动脉瘤，按体重同样分为3组：〈65kg，65-75kg，〉75kg，分别采用低管电流为50、75、100mAs，记录并分析相应CTDI和DLP，评价图像质量及满足诊断率。结果初步研究采用25、50、75mAs的CTDI仅为常规剂量175mAs的11．3％、29．0％和42．7％，各组DLP值与常规剂量组相比差异均有统计学意义（均P〈0．001），但25mAs组的诊断符合率仅为60．0％，50、75mAs低剂量组的图像满足诊断率均为85．0％，未达到100％。第2步研究采用50、75、100mAs的CTDI分别为常规剂量的29．0％、42．7％和57．3％，各低剂量组DLP与常规剂量组两两比较差异均有统计学意义（均P〈0．01），且各组图像满足诊断率均达到100％。轴位及各种三维重建图像显示良好。结论16层螺旋CT主动脉低剂量扫描满足诊断的最低管电流根据不同体重可采用50—100mAs。夹层动脉瘤应采用略高于其他主动脉病变的管电流。100mAs的低管电流则可满足任意体重及任意主动脉病变的成像与诊断。

Objective To study the effects of 16-multi-detector row CT （MDCT） aortography with lower tube current in diagnosis of aortic diseases. Methods The study was conducted in 2 steps. In the first step, 58 patients with suspicious aortic disease or after operation on the aorta underwent 16-MDCT aortography for 70 times. Ten of them underwent scanning with conventional tube current of 175 mAs and the other 60 patients were divided into 3 groups according to their bogy weights ： 〈 65 kg group （ n = 20 ） receiving the lowest tube current of 25 mAs, 65 - 75 kg group （ n = 20） receiving the lowest tube current of 50 mAs, and 〉 75 kg group （ n = 20） receiving the lowest tube current of 75 mAs. In the second step 60 patients with dissecting aneurysm, underwent 16-MDST aortography and were divided into 3 groups according to their body weight too ： 〈 65 kg group （ n = 20） receiving the lowest tube current of 50 mAs, 65 - 75 kg group （n = 20） receiving the lowest tube current of 75 mAs, and 〉 75 kg group （n = 20） receiving the lowest tube current of 100 mAs, all 25 mAs more compared with the corresponding groups in the first step. The weighted CT dose index （CTDI）, scanning length, and dose length produce （DLP） were recorded. The diagnostic accuracy rates of the images from the low dose groups were compared with those of the higher dose groups. Results The data of the first step showed that the CTDI values of the patients who received 25 mAs,50 mAs, and 75 mAs tube current were 11.3%, 29.0%, and 42.7% that of the conventional tube current group （ all P 〈 0. 001 ）, and the DLP values of the 3 low dose groups were also significantly lower than that of the conventional tube current group （ all P 〈 0. 001 ）. The diagnostic accuracy rate of the 25 mAs, 50 mAs, and 75 mAs groups were 60%, 85%, and 85% that of the conventional tube current group. The results of the second step showed that the CTDI values of the 50 mAs, 75 mAs, and 100 mAs groups were 29.0%, 42.7%, and 57.3% that of the conventional tube current group respectively, and the DLP values of the 3 low dose groups were also significantly lower than that of the conventional group （ all P 〈 0. 001 ） ; and the 50 mAs, 75 mAs, and 100 mAs groups all showed good three-dimensional reconstruction imaging qualities, all with the diagnostic accuracy rate of 100%. The crossing section and three-dimensional images all showed excellent diagnostic image quality. Conclusion 16-MDCT aortography with the tube current at the doses 50 mAs to 100 mAs suffices to diagnose aortic diseases in patients with different body weights. Higher tube current should be used in dissecting aneurysm. The tube current at the dose of 100 mAs satisfies the imaging and diagnosing of all kinds of aortic diseases in the patients with any body weight.