64层螺旋CT自动毫安技术对降低下肢动脉 血管成像辐射剂量的研究

目的 探讨64层螺旋CT自动毫安技术(ATCM)对降低下肢动脉血管成像辐射剂量的可行性。方法 通过预实验改变噪声指数(NI)调节管电流,得出NI值为10 HU时图像质量与辐射剂量匹配较佳。搜集52例疑有下肢动脉闭塞糖尿病及高血压病患者病例,随机分为实验组和对照组行自肾下腹主动脉至足底的CT容积扫描,每组病例26例。对照组采用常规固定300 mA(FM组),实验组采用NI为10 HU的自动毫安(ATCM组)技术。分别选择肾下腹主动脉、髋关节水平股动脉、 NFDB1 动脉及踝关节胫前动脉平面作为观察平面,对两种毫安技术的图像质量、图像噪声和辐射剂量均采用 t 检验方法进行统计学分析。结果 FM组的辐射剂量CTDI_vol为10.81 mGy,平均DLP为(1280.4±124.7)mGy·cm,ATCM组的平均CTDI_vol为(5.14±1.23)mGy,平均DLP为(582.86±150.41)mGy·cm,比FM组降低约54.4%,两组差异有统计学意义(CTDI_vol、DLP的 t 值分别为13.13、17.36, P 值均<0.05)。FM组的4个选取平面图像噪声分别为13.8±4.04、14.53±2.79、5.69±1.38、(4.75±1.38) HU。ATCM组分别为10.76±2.11、12.13±2.96、10.47±2.96、(6.17±1.53) HU,两组差异有统计学意义( t 值分别为2.911、3.038、7.287及3.186, P 值均<0.05),ATCM组肾下腹主动脉、髋关节水平股动脉层面的图像噪声较FM组的低,而 NFDB1 动脉、踝关节胫前动脉层面的图像噪声较FM组的高,ATCM组图像噪声变异度小,图像更加均匀。FM组图像质量评分平均为2.654±0.562,ATCM组图像评分平均为2.462±0.582,两组图像质量评分差异无统计学意义( t =1.21, P ＞0.05)。结论 使用噪声指数为10的下肢动脉ATCM技术,在保证图像质量的情况下可以降低辐射剂量约54.4%。

Feasibility study of automatic tube current modulation technique of 64-slices CT for reducing radiation doses of lower extremity arterial imaging

Objective To investigate the value of automatic tube current modulation technique of 64-slices CT for reducing radiation doses of lower extremity arterial imaging. Methods Adjustment tube current through the pre-test changes in the noise index (NI), obtained the image quality and radiation dose with better matches when NI value of 10 HU. Fifty-two diabetic and hypertensive patients suspicious of having lower extremity occlusive disease underwent 64-slices CT volume scan arranged from infra-renal aorta to feet and separated random into 2 groups. The experimental group of 26 patients(FM) used fixed tube current of 300 mA technique, and the the follow-up of 26 patients (control group) used automatic tube current modulation (ATCM) technique with NI= 10. We selected the observing levels at infra-renal aorta, femoral artery of hip joint level, popliteal artery and anterior tibial artery at ankle level. Both sets of image quality, image noise and radiation dose were analyzed by using t-test. Results The radiation dose level of ATCM group[ CTDI_(vol): 10.81 mGy,DLP: (1280.40±124.70) mGy·cm] was lower than FM group[CTDI_(vol): (5.14±1.23) mGy, DLP: (582.86±150.41) mGy·cm] by 54.4% , difference between the two groups was statistically significant(t_(CTDIvol) = 13.13, t_(DLP) = 17.36, P<0.05). The difference of image noise in four levels between ATCM group [10.76 ± 2. 11、 12.13 ±2.96,10.47 ±2.96,(6.17 ± 1.53) HU] and FM group[ 13.80 ± 4.04,14.53 ± 2.79,5.69 ± 1.38、(4.75±1.38) HU] was significant (t =2.991,3.038,7.287,3.186, P < 0.05) .The image noise of ATCM group were lower than FM group at infra-renal aorta level and femoral artery of hip joint level,but ATCM group were higher than FM group at popliteal artery level and anterior tibial artery at ankle level. The variations of noise were reduced with the ATCM technique with more uniform image quality. There was no significant difference in image quality score between the ATCM group(2.462 ± 0.582) and FM group(2.654 ± 0.562) (t = 1.21, P > 0.05). Conclusion Lower extremity CT scanning with automatic tube current modulation technique (NI = 10) can greatly reduce the radiation exposure by 54.4% and maintain the equivalent image quality.