A study of clinical appliance of multidetector-row CT in the maxillo-facial region

本研究旨在明确颌面部多层螺旋CT临床应用的最佳扫描条件。为评价颌骨畸形或颞下颌关节紊乱病患者的颞下颌关节（TMJ）骨质改变，对该模型的TMJ区域进行了不同条件下的扫描。对每一次扫描的CT数据进行4个不同的重建间隔的重建，然后将重建后的图像制成多平面重建（MPR）图像。MPR冠状位和矢状位图像是评价颞下颌关节骨性结构的最佳图像，最佳组合为：通过对管电流、螺距、重建函数、重建间隔等参数的分析，确定了TMJ区的最佳扫描方案，扫描范围：体模中TMJ区50mm（恒定条件）管电位：120kV（恒定条件）CT光束准直：1.25mm（恒定条件）管电流：80mA（非恒定条件）螺距：3（非恒定条件）重建间隔：0.25mm在上述条件组合下，扫描时间、CT剂量指数（CTDI）和剂量长度乘积（DLP）分别为14.8秒、25.08mGy、和139.15mGycm。在相同重建间隔条件下比较图像，提示管电流并不总是影响图像的易观察性。可以认为，重建间隔更能有效地获得清晰的MPR图像。

This study was carried out mainly to make clear the optimal scanning conditions in clinical appliance of multidetector-row CT in the maxillo-facial region. Thinking of the appliance to evaluation of bone change of temporomandibular joint(TMJ) in the patients with jaw deformity or temporomandibular joint disorder, the region of TMJs of the phantom was scanned in several conditions. CT data obtained from every scanning was reconstructed in the different reconstruction interval of 4, then multi planar reconstruction(MPR) images were made with the reconstructed images. Coronal and sagittal images of MPR was used to estimate better imagse to evaluate bone in TMJ, the most suitable combination of the conditions i.s. tube current, helical pitch, reconstruction function, and reconstruction interval.Optimal scanning protocol of the region of TMJs was considered as follows.Scanning range : 50mm of the region of TMJ in the phantom (constant condition)Tube potential : 120kV (constant condition)CT beam collimation : 1.25mm (constant condition)Tube current : 80mA (inconstant condition)Helical pitch : 3 (inconstant condition)Reconstruction interval : 0.25mm (inconstant condition)In the combination of the conditions as above, scanning time, computed tomography dose index(CTDI), and dose-length product(DLP) were 14.8 seconds, 25.08mGy, and 139.15mGycm, respectively. Comparing images in the same condition of reconstruction interval, it might be suggested that tube current was not always effect on the ease of observation of images. It could be considered that reconstruction interval is more effective to make clear MPR images.