锥形束CT不同扫描参数对下颌骨骨微结构显示的影响

Effects of different scanning parameters of cone beam CT on displaying microstructure of mandible

目的比较锥形束CT(cone beam CT,CBCT)不同扫描参数对下颌骨颏孔前区域骨微结构显示的影响,为合理选择CBCT扫描参数提供基础。方法获得南京大学医学院附属口腔医院伦理委员会批准,离体研究使用CBCT对8个干燥人下颌骨离体标本进行ProMax 3D Mid扫描,采用5组方案进行扫描,分别为组A:90 kV/6.3 mA,组B:90 kV/8.0 mA,组C:90 kV/10.0 mA,组D:75 kV/8.0 mA,组E:60 kV/8.0 mA,扫描共得到40个CBCT图像;并记录不同扫描条件下的体表入射剂量(entrance surface dose,ESD)及CT剂量指数(computed tomography dose index,CTDI)。将收集的原始CBCT图像导入图像分析软件(Hiscan Analyzer)测量下颌骨兴趣区的4个骨微结构测量参数,分别是骨小梁厚度(trabecular thickness,Tb.Th),骨小梁数目(trabecular number,Tb.N),骨小梁间隙(trabecular space,Tb.Sp),骨小梁体积百分数(bone volume/tissue volume,BV/TV)。回顾性收集临床种植患者分别使用90 kV/6.3 mA、90 kV/8.0 mA、90 kV/10.0 mA中任一组扫描条件得到的CBCT图像共计108个,同样测量下颌骨兴趣区的上述4个参数。使用SPSS 26.0分别比较离体标本及临床患者CBCT图像的4个骨微结构测量参数的差异。结果离体标本研究结果显示,球管电压及球管电流减低均会导致ESD及CTDI剂量指数下降。当球管电压保持90 kV,球管电流改变时:BV/TV、Tb.N、Tb.Th数值随球管电流增大而增大;Tb.Sp数值随球管电流增大而减小,但4个骨形态参数均无统计学差异(P>0.05)。当球管电流保持8.0 mA,球管电压改变时:BV/TV、Tb.N随球管电压增大而减小,Tb.Sp数值随球管电压增大而增大,且BV/TV、Tb.N、Tb.Sp具有统计学差异(P<0.05)。临床患者CBCT扫描时,当球管电压为90 kV,而球管电流不同时(6.3、8.0、10.0 mA),4个骨形态参数均不具有统计学差异(P>0.05)。结论本研究中,球管电压固定为90 kV、球管电流增大时下颌骨前区骨微结构显示无差异,临床患者CBCT扫描需显示下颌骨前区骨微结构时可适当减少球管电流以降低患者所受辐射剂量,推荐使用参数90 kV,6.3 mA。

Objective To compare the effect of different scanning parameters of cone beam computed tomography(CBCT)on displaying trabecular microstructure in the anterior region of the mental foramen of the mandible,and to provide a basis for the rational selection of CBCT scanning parameters.Methods This study was approved by the Ethics Committee of the Affiliated Stomatological Hospital,Medical School of Nanjing University.An in vitro study was con⁃ducted using CBCT(ProMax 3D Mid)to scan eight dry human mandibular specimens with five scanning protocols:Group A:90 kV/6.3 mA,Group B:90 kV/8.0 mA,Group C:90 kV/10.0 mA,Group D:75 kV/8.0 mA,and Group E:60 kV/8.0 mA,resulting in a total of 40 CBCT images.Entrance surface dose(ESD)and computed tomography dose index(CTDI)under different scanning conditions were recorded.The original CBCT images were imported into the image anal⁃ysis software(Hiscan Analyzer)to measure four trabecular bone microstructural parameters in the region of interest of the mandible:trabecular thickness(Tb.Th),trabecular number(Tb.N),trabecular space(Tb.Sp),and bone volume/tissue volume(BV/TV).A total of 108 CBCT images were retrospectively collected from clinical implant patients using any of the 90 kV/6.3 mA,90 kV/8.0 mA,or 90 kV/10.0 mA scanning conditions,and the above four parameters of the region of interest of the mandible were also measured.SPSS 26.0 software was used to compare the differences in the four tra⁃becular bone microstructural parameters between the CBCT images of the mandibular specimens in vitro and clinical pa⁃tients in vivo.Results The in vitro study results showed that reducing the tube voltage and tube current would lead to a decrease in the ESD and CTDI.When the tube voltage was maintained at 90 kV and the tube current was changed,BV/TV,Tb.N,and Tb.Th values increased with the increase of tube current;Tb.Sp values decreased with the increase of tube current,but there was no statistically significant difference in the four bone morphological parameters(P>0.05).When the tube current was maintained at 8.0 mA and the tube voltage was altered,BV/TV and Tb.N decreased with the increase of tube voltage,Tb.Sp values increased with the increase of tube voltage,and BV/TV,Tb.N,and Tb.Sp showed statistically significant differences(P<0.05).In clinical patients undergoing CBCT scanning,when the tube voltage was 90 kV and the tube current was different(6.3,8.0,10.0 mA),there was no statistically significant difference in the four bone morphological parameters(P>0.05).Conclusions In this study,when the tube voltage was fixed at 90 kV,there was no difference in the trabecular microstructure of the anterior region of the mandible when the tube current was in⁃creased.When CBCT scanning of clinical patients needs to show the trabecular microstructure of the anterior region of the mandible,the tube current can be appropriately reduced to decrease the radiation dose received by the patient.Thus,it is recommended to use the parameters 90 kV and 6.3 mA for CBCT scanning.