低剂量CT扫描在64层螺旋CT头颈部数字减影CTA中的可行性研究

Study on the Feasibility of Low-Dose 64-Slice Spiral Scanning for Head and Neck Digital Subtraction CT Angiography

目的应用不同噪声指数(NI)值的联合调制自动毫安技术(ATCM)进行低剂量扫描,以探讨64层螺旋CT头颈部数字减影CTA(DSCTA)中联合调制合理低剂量的可行性。方法 90例因临床怀疑头颈部血管病变行头颈部DSCTA检查的患者,按完全随机设计分为3组,每组30例。所有患者均采用64层螺旋CT联合调制ATCM技术,以不同的NI值(A组:NI=6.0 HU,B组:NI=8.0 HU,C组:NI=10.0 HU)进行扫描,其他参数3组均保持一致。记录每次扫描的平均管电流(mAs)、CT容积剂量指数(CTDIvol)及剂量长度乘积(DLP)和有效剂量(ED)。分别选择头颅、颈部和肩关节层面作为观察平面,对3组患者的图像质量评分、图像噪声、mAs、CTDIvol及DLP和ED的差异采用ANOVA法或Kruskal-Wallis法进行统计学分析。结果 A组mAs值(123.03±6.17)mAs、CTDIvol值(46.32±3.10)mCy及DLP值(1703.40±176.70)mGy·cm和ED值(3.92±0.41)mSv均最大;B组mAs值(92.78±5.41)mAs、CTDIvol值(36.13±1.95)mCy及DLP值(1340.09±122.59)mGy·cm和ED值(3.08±0.28)mSv均居中;C组mAs值(83.08±9.25)mAs、CTDIvol值(32.56±3.26)mCy及DLP值(1199.86±135.93)mGy·cm和ED值(2.76±0.31)mSv均最小(P均=0.000),辐射剂量:C组较A组降低30%、C组较B组降低10%、B组较A组降低21%。3组图像质量评分分别为A组(4.20±0.66)分、B组(4.03±0.67)分和C组(3.83±0.75)分,差异无统计学意义(P﹥0.05)。3组头颅层面mAs值分别为A组(104.77±12.96)mAs、B组(83.03±6.86)mAs和C组(70.56±5.72)mAs,A组最大,C组最小(P均<0.05);图像噪声分别为A组(8.16±1.63)、B组(9.63±1.03)和C组(10.54±1.72),A组最小,C组最大(P均<0.05)。3组颈部层面mAs值分别为A组(99.32±9.80)mAs、B组(62.07±4.46)mAs和C组(58.84±5.47)mAs,A组最大,C组最小(P均<0.05);图像噪声分别为A组(4.93±0.75)、B组(6.16±0.87)和C组(6.43±0.84),A组较B、C组小(P均=0.000),B、C组差异无统计学意义(P﹥0.05)。3组肩关节层面mAs值分别为A组(147.30±1.24)mAs、B组(146.74±1.17)mAs和C组(146.70±1.27)mAs,图像噪声分别为A组(10.97±1.61)、B组(11.49±1.28)和C组(11.61±1.59),差异均无统计学意义(P均﹥0.05)。结论 64层螺旋CT头颈部DSCTA中联合调制低剂量成像是可行的,应用NI为10.0 HU的低剂量CT扫描可以满足临床诊断需要。

Objective To investigate the clinical feasibility of low-dose 64-slice spiral CT scanning for head and neck digital subtraction CT angiography （DSCTA） by combination use of automatic tube current modulation （ATCM） technique with the different noise index （NI）. Methods Ninety patients with clinically-suspected head and neck vascular diseases underwent DSCTA examination, and the patients were randomly and equally divided into 3 groups with 30 patients in each group. 64-slice spiral CT scanning was performed in all patients by combination use of ATCM technique with different NI （group A, NI = 6.0 HU ; group B, NI = 8.0 HU and group C, NI = 10.0 HU）, while the other scan parameters were held constant. Results In group A, the mean mAs value was （123.03 ± 6.17） mAs, the CTDIvol value was （46.32 ± 3.10） mCy, the DLP value was （ 1703.40 ± 176.70） mGy · cm and the ED value was （3.92 ±0.41 ） mSv, and all the values of above parameters of group A were the highest in the three groups. The results in group B were as follows： mean mAs value = （92.78 ±5.41 ） mAs, CTDIvoI value = （36.13 ± 1.95） mCy, DLP value = （ 1340.09 ± 122.59） mGy · cm and the ED value = （3.08 ± 0.28 ） mSv, the values being at the middle level among the three groups. The results in group C were as follows ： mean mAs value = （83.08 ± 9.25 ） mAs, the CTDIvol value = （32.56 ± 3.26） mCy, the DLP value = （ 1199.86 ± 135.93 ） mGy · cm and the ED value = （2.76 ± 0.31 ） mSv, the above values being the lowest in the three groups （ P = 0. 000）. For the respect of radiation dosage, group C showed a reduction of 30% and 10% when compared with group A and group B respectively, and group B showed a reduction of 21% when compared with group A. The image quality score of group A, B and C was （4.20 ± 0.66） , （4.03 ± 0.67） and （3.83 ± 0.75 ） respectively, the differences between each other among the three groups were not statistically significant （ P 〉 0.05 ）. The mean mAs value at the head level in group A, B and C was （104.77 ± 12.96） mAs, （83.03 ± 6.86） mAs and （70.56 ± 5.72） mAs respectively, with the value of group A being the largest and group C the smallest （P 〈0.05 in all）. The image noise score at the head level in group A, B and C was （8.16 ± 1.63 ）, （9.63 ± 1.03 ） and （ 10.54 ± 1.72） respectively, with the image noise score of group A being the smallest and group C the largest （P 〈0.05 in all）. The mean mAs value at the neck level in group A, B and C was （99.32 ± 9.80） mAs, （62.07 ± 4.46） mAs and （58.84 ± 5.47 ） mAs respectively, with the value of group A being the largest and group C the smallest （P 〈 0.05 in all ）. The image noise score at the neck level in group A, B and C was （ 4.93 ± 0.75 ）, （6.16 ± 0.87 ） and （ 6.43 ± 0.84） respectively, with the image noise score of group A being the smallest （ P = 0.000 ） , and the difference in the image noise score between group B and C was not statistically significant （ P 〉 0.05）. The mean mAs value at the shoulder level in group A, B and C was （ 147.30 ± 1.24） mAs, （ 146.74 ± 1.17 ） mAs and （ 146.70 ± 1.27 ） mAs respectively, and the image noise score at the shoulder level in group A, B and C was （ 10.97 ± 1.61 ） , （ 11.49 ± 1.28 ） and （ 11.61 ± 1.59 ） respectively, and the differences between each other among the three groups were not statistically significant （ P 〉 0.05 in all）. Conclusion It is feasible to adopt low-dose 64-slice spiral CT scanning for the performance of head and neck digital subtraction CT angiography by combination use of automatic tube current modulation technique. Scan protocol of NI = 10.0 HU can ensure a satisfactory image quality for diagnostic purpose.