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BACKGROUND Skeletal mandibular protrusion would influence to the muscle fatigue of the masticatory muscles. Establishing a diagnostic procedures combining physiological and biochemical information is necessary for quantitative evaluation of masticatory muscle fatigue. OBJECTIVE The transverse relaxation time (T2 time) of muscle functional magnetic resonance imaging (mfMRI), and 31 P-magnetic resonance spectroscopy (MRS) were used to investigate the reliability as parameters for measuring the masseter muscle in patients with skeletal mandibular prognathism. METHOD The subjects were 19 patients diagnosed as skeletal mandibular protrusions and 19 healthy subjects as a control group. Transverse relaxation time (T2 value) determined by mfMRI along with creatine phosphate (PCr) and inorganic phosphorus (Pi) determined by 31 P-MRS before, during, and after clenching were used for molecular imaging of muscle fatigue. RESULTS The average T2 value of the patient group was significantly higher than that of the healthy control group at rest. Furthermore, the average T2 value transiently increased in both groups during experimental clenching. The PCr and Pi showed a tendency toward a transient decrease and increases, respectively. The pH in the masseter muscle showed a transient decrease in both groups prior to and following experimental clenching. The pH in the masseter muscle of the patient group was significantly lower than that in the healthy control group at rest and recovery. CONCLUSION We showed mfMRI and 31 P-MRS are useful for evaluating masseter fatigue during clenching, and the masseter muscle in the prognathic patients showed more severe fatigue than the healthy controls.

The basic principles and diagnostic methods of magnetic resonance imaging (MRI) for beginning surgeons are described in this review. MRI is an important technique that is essential for diagnoses in the maxillofacial area. It is a scanning method that obtains tomographic images of the human body using a magnetic field. In contrast to computed tomography, it does not utilize X-rays and, therefore, represents a noninvasive test that lacks radiation exposure. It is particularly effective for soft-tissue diagnoses. MRI involves imaging protons in vivo. Protons emit a signal when a radio frequency pulse is applied in a magnetic field; the MRI device then forms an image from these signals. The basic images produced are T1- and T2-weighted images; comparison of these images is the first step of MRI-based diagnosis. Short-T1 inversion recovery images, which eliminate the signal from fat, are also useful for diagnosis. Gadolinium is used as a contrast agent for MRI. Taking sequential images at fixed intervals while injecting the contrast agent and then graphing the contrast effect along the time axis produces a time–signal intensity curve, which is useful for identifying features such as malignant neoplasms based on the graph pattern.

To compare magnetic resonance imaging (MRI) findings between patients with malignant lymphoma (ML) and squamous cell carcinoma (SCC) in the head and neck regions, and to show the characteristic findings for ML. We analyzed 10 lesions in nine patients with ML and 25 lesions in 25 patients with SCC. Diffusion-weighted imaging, T1-weighted imaging, and T2-weighted imaging were performed for all lesions. We estimated the apparent diffusion coefficients (ADCs) with b-factors of 0, 500, and 1000 s/mm2, and obtained the means and standard deviations. In 29 cases, dynamic contrast-enhanced MRI (DCE-MRI) was performed and time–intensity curves were obtained. The peak time, maximum-to-initial ratio (MI ratio), end-to-maximum ratio, and end-to-initial ratio (EI ratio) were estimated. Receiver-operating characteristic analyses were performed to estimate the diagnostic power for these indices. The mean ADC for ML (0.762 ± 0.126 × 10−3 mm2/s) was significantly lower than that for SCC (1.24 ± 0.22 × 10−3 mm2/s, p

The aim of this study was to display the lingual artery superimposed on the anatomical image and to confirm its course and relation to the adjacent structures, noninvasively. Nineteen volunteers participated in the magnetic resonance imaging (MRI) study and one was excluded for excessive movement during scanning. A three-dimensional phase-contrast sequence (3D-PC) of magnetic resonance angiography (MRA) was used for vessel images, and a 3D-T1 high-resolution volume examination (THRIVE) was used for anatomical images. Colour-coded vessel images from 3D-PC MRA were superimposed on the 3D volume anatomical images, and the arterial course and relation to the adjacent structures were confirmed with multiplanar reconstructed cross-sectional (MPR) images. 3D-PC MRA images visualized the lingual artery in all 18 subjects and the sublingual artery in 14 subjects. In seven of 18 cases the bilateral sublingual arteries were shown to run side by side but had no contact with the sublingual veins. They ran together with the sublingual veins in four cases. Three cases showed irregular patterns. The bilateral sublingual arteries could not be identified in four cases. 3D-PC MRA images of the lingual artery superimposed on the anatomical images may be clinically useful to confirm its course and relationship to the adjacent structures before surgery, in order to prevent haemorrhage.

Background Diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) can be used to evaluate changes that accompany skeletal muscle contraction. Purpose To investigate whether jaw opening or closure affect the diffusion parameters of the masseter muscles (MMs). Material and Methods Eleven healthy volunteers were evaluated. Diffusion-tensor images were acquired to obtain the primary (λ1), secondary (λ2), and tertiary eigenvalues (λ3). We estimated these parameters at three different locations: at the level of the mandibular notch for the superior site, the level of the mandibular foramen for the middle site, and the root apex of the mandibular molars for the inferior site. Results Both λ2 and λ3 during jaw opening were significantly lower than that at rest at the superior ( P = 0.006, P < 0.0001, respectively) and middle site ( P = 0.004, P = 0.0001, respectively); however, the change in λ1 was not significant. At the lower site, no parameter was significantly different at rest and during jaw opening. There was no significant difference in T2 between at rest (40.3 ± 4.4 ms) and during jaw opening (39.2 ± 2.7 ms; P = 0.12). The changes induced by jaw closure were marked at the inferior site. In the middle and inferior sites, the three eigenvalues were increased by jaw closure, and the changes in λ1 ( P = 0.0145, P = 0.0107, respectively) and λ2 ( P = 0.0003, P = 0.0001) were significant (especially λ2). Conclusion The eigenvalues for diffusion of the MM were sensitive to jaw position. The recruitment of muscle fibers, specific to jaw position, reflects the differences in changes in muscle diffusion parameters.