Diffusion-weighted magnetic resonance imaging of the oral and maxillofacial region: optimal fat suppression method.

OBJECTIVE: To compare 3 fat suppression methods-water excitation (WE), chemical shift selective (CHESS), and short T1 inversion recovery (STIR)-for optimal image quality and apparent diffusion coefficient (ADC) values with magnetic resonance imaging (MRI) using diffusion-weighted imaging (DWI) of the oral and maxillofacial region. STUDY DESIGN: In total, 53 patients with 73 lesions were enrolled in this study. MRI using DWI protocols with the 3 fat suppression methods were performed in addition to a conventional MRI protocol. The diagnostic image quality of lesions, image uniformity, degree of image artifacts, and ADC values of the lesions were evaluated. Average visual scores and ADC values were compared, and post hoc pairwise comparisons were performed, with the level of significance set at P < .0167. RESULTS: Diagnostic image quality was not significantly different among the fat suppression methods (P ≥ .042). Image uniformity was significantly higher (P < .001), and the degree of image artifacts was significantly lower (P < .001), in images using the STIR method. Mean ADC values did not differ significantly among the 3 methods. CONCLUSIONS: The STIR method was the most useful fat suppression method for DWI of the oral and maxillofacial region because of its high level of image uniformity and few image artifacts.

T2 relaxation times of the retrodiscal tissue in patients with temporomandibular joint disorders and in healthy volunteers: a comparative study.

OBJECTIVE: The aims of this study were to compare the temporomandibular joint (TMJ) retrodiscal tissue T2 relaxation times between patients with temporomandibular disorders (TMDs) and asymptomatic volunteers and to assess the diagnostic potential of this approach. STUDY DESIGN: Patients with TMD (n = 173) and asymptomatic volunteers (n = 17) were examined by using a 1.5-T magnetic resonance scanner. The imaging protocol consisted of oblique sagittal, T2-weighted, 8-echo fast spin echo sequences in the closed mouth position. Retrodiscal tissue T2 relaxation times were obtained. Additionally, disc location and reduction, disc configuration, joint effusion, osteoarthritis, and bone edema or osteonecrosis were classified using MRI scans. The T2 relaxation times of each group were statistically compared. RESULTS: Retrodiscal tissue T2 relaxation times were significantly longer in patient groups than in asymptomatic volunteers (P < .01). T2 relaxation times were significantly longer in all of the morphologic categories. The most important variables affecting retrodiscal tissue T2 relaxation times were disc configuration, joint effusion, and osteoarthritis. CONCLUSIONS: Retrodiscal tissue T2 relaxation times of patients with TMD were significantly longer than those of healthy volunteers. This finding may lead to the development of a diagnostic marker to aid in the early detection of TMDs.

Effectiveness of the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique for reducing motion artifacts caused by mandibular movements on fat-suppressed T2-weighted magnetic resonance (MR) images.

PURPOSE: To compare a fat-suppressed T2-weighted periodically rotated overlapping parallel lines with enhanced reconstruction (T2W-PROPELLER) sequence with a fat-suppressed T2-weighted fast spin-echo (T2W-FSE) sequence in the oral and maxillofacial regions for the evaluation of the presence of motion artifacts caused by mandibular movements. METHODS: Fifty-six healthy adult volunteers were examined in a closed mouth position and then with three different rhythmical mandibular movements throughout MR scanning: open-close movement (movement 1), lateral movement (movement 2) and open-close and lateral movement (movement 3). All subjects were scanned first with fat-suppressed T2W-FSE and then with fat-suppressed T2W-PROPELLER while performing the same movements. Motion artifacts, including ghosting or pulsation artifacts, streak artifacts, susceptibility artifacts and the overall image quality were independently evaluated by two oral and maxillofacial radiologists using a five-point scale. The score graded by the two observers was averaged. RESULTS: The inter-observer agreement was almost perfect for all evaluated items (κ ≥ 0.81). The T2W-PROPELLER images showed significantly fewer ghosting artifacts than T2W-FSE images in subjects performing the mandibular movements throughout MR scanning (P < .001). T2W-PROPELLER images also showed significantly fewer pulsation artifacts than T2W-FSE images, regardless of the performance of a movement, throughout MR scanning (P < .001). Finally, the T2W-PROPELLER images showed a significantly better overall image quality than T2W-FSE images in subjects performing movements 2 or 3 throughout MR scanning (P < .001). CONCLUSION: The PROPELLER technique was found to be effective in reducing the motion artifacts caused by mandibular movements on fat-suppressed T2W MR images in the oral and maxillofacial regions.

Accuracy and precision of manual segmentation of the maxillary sinus in MR images-a method study.

OBJECTIVE: To assess the accuracy and precision of segmentation of the maxillary sinus in MR images to evaluate the potential usefulness of this modality in longitudinal studies of sinus development. METHODS: A total of 15 healthy subjects who had been both craniofacial CT and MR scanned were included and the 30 maxillary sinus volumes were evaluated using segmentation. Two of the authors did segmentation of MRI and one of these authors did double segmentation. Agreement in results between CT and MRI as well as inter- and intraexaminer errors were evaluated by statistical and three-dimensional analysis. RESULTS: The intraclass correlation coefficient for volume measurements for both method error, inter- and intraexaminer agreement were > 0.9 [maximal 95% confidence interval of 0.989-0.997, p < 0.001] and the limit of agreement for all parameters were < 5.1%. Segmentation errors were quantified in terms of overlap [Dice Coefficient (DICE) > 0.9 = excellent agreement] and border distance [95% percentile Hausdorff Distance (HD) < 2 mm = acceptable agreement]. The results were replicable and not influenced by systematic errors. CONCLUSION: We found a high accuracy and precision of manual segmentation of the maxillary sinus in MR images. The largest mean errors were found close to the orbit and the teeth. Advances in knowledge: MRI can be used for 3D models of the paranasal sinuses with equally good results as CT and allows longitudinal follow-up of sinus development.