1. 4次元MRIを用いた顎関節部の撮像条件の検討 SI-dとSNR-dによる評価

「I. Purpose」The aim of this study was to establish the optimal contrast of the imaging characteristic for 4 Dimensional MRI with steady-state free precession (SSFP) sequence for evaluation of the TMJ during mandibular movement especially the position and morphology of the articular disc. 「II. Materials and Methods」This study examined 12 TMJs from 6 subjects, mean age of 25.67 years old, ranging from 20 to 32 years. All subjects had no abnormality in the Temporomandibular function. MRI examinations were performed on a 1.5T MR System (Philips) with SSFP sequence and a phased array coil. Sagittal images of each TMJ were taken in the closed mouth position by setting various flip angles (FA) with 10-degree interval between 10 and 100 degrees. The contrasts of images were evaluated in 4 main anatomical structures of TMJ; posterior band of articular disc, retrodiscal tissues, condylar head, and lateral pterygoid muscle. Image quality was evaluated by the signal intensity (SI-d) and signal-to-noise ratio (SNR-d). The average values of SI-d and SNR-d of total subjects were analyzed by 2-way ANOVA with TMJ structures and flip angles as 2 factors, and Bonferroni multiple comparison tests. 「III. Results」Main anatomical structures of TMJ mostly had the highest SI-d and SNR-d values at FA 30 and 40 degrees. There were significant differences between SI-d of articular disc and SI-d of other structures, the most was at FA 40 degrees, the next were at FA 30 and 50 degrees respectively, and no significant difference of SNR-d values between FA 30 and 40 degrees. 「IV. Conclusion」These results suggest that flip angle approximately 30 to 40 degrees is appropriate for obtaining the optimal contrast of the imaging characteristic for 4D MR with SSFP sequence of the TMJ imaging, for evaluation of TMJ during its functions.