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.

Deep convolutional neural network for reduction of contrast-enhanced region on CT images.

This study aims to produce non-contrast computed tomography (CT) images using a deep convolutional neural network (CNN) for imaging. Twenty-nine patients were selected. CT images were acquired without and with a contrast enhancement medium. The transverse images were divided into 64 × 64 pixels. This resulted in 14 723 patches in total for both non-contrast and contrast-enhanced CT image pairs. The proposed CNN model comprises five two-dimensional (2D) convolution layers with one shortcut path. For comparison, the U-net model, which comprises five 2D convolution layers interleaved with pooling and unpooling layers, was used. Training was performed in 24 patients and, for testing of trained models, another 5 patients were used. For quantitative evaluation, 50 regions of interest (ROIs) were selected on the reference contrast-enhanced image of the test data, and the mean pixel value of the ROIs was calculated. The mean pixel values of the ROIs at the same location on the reference non-contrast image and the predicted non-contrast image were calculated and those values were compared. Regarding the quantitative analysis, the difference in mean pixel value between the reference contrast-enhanced image and the predicted non-contrast image was significant (P < 0.0001) for both models. Significant differences in pixels (P < 0.0001) were found using the U-net model; in contrast, there was no significant difference using the proposed CNN model when comparing the reference non-contrast images and the predicted non-contrast images. Using the proposed CNN model, the contrast-enhanced region was satisfactorily reduced.

Evaluation of mouthpiece fixation devices for head and neck radiotherapy patients fabricated in PolyJet photopolymer by a 3D printer.

PURPOSE: The purpose of our study was to evaluate the usefulness of a biocompatible class VI resin PolyJet photopolymer Objet MED610 (MED610)-made mouthpiece fabricated using a 3D printer as a fixation device for head and neck radiotherapy patients. METHODS: Five mouthpieces made of GC Exafine putty type (GCEP) were fabricated from five dry skull bones. After computed tomography reconstruction of the GCEP-made mouthpiece and its surface extraction, the MED610-made mouthpieces were replicated. The sizes of the GCEP and MED610 mouthpieces were measured with a vernier caliper in width, length, and height, respectively. The volumes of these mouthpieces were measured by Archimedes' principle using pure water. For dose evaluation, the GCEP and MED610 mouthpieces were placed in the same part of a water phantom, and a 4-MV X-ray beam was located at the left maxillary gingiva, buccal mucosa, and oral floor. The dose for the planning target volume (PTV) was evaluated. RESULTS: The differences in the mean size and volume between the GCEP and MED610 mouthpieces were 0.03 mm and 0.21 cm3, respectively. Compared with the conventional GCEP mouthpiece, the dose absorption in the MED610 mouthpiece was closer to that in only water. When the mouthpiece was within the PTV margin, the minimum coverage dose at 95% of the PTV increased by 2.4% in the maxillary gingiva and by 3.6% in the buccal mucosa. CONCLUSION: A 3D printer can construct a mouthpiece accurately. The MED610 mouthpiece is suitable for use in dosimetry in head and neck radiotherapy.

Diffusion-weighted MR microimaging of the lacrimal glands in patients with Sjogren's syndrome.

OBJECTIVE: The purpose of this study was to detect quantitative diffusion-weighted abnormalities in the lacrimal glands of patients with Sjogren's syndrome. MATERIALS AND METHODS: Diffusion-weighted MRI was performed on 31 healthy volunteers and 11 Sjogren's syndrome patients with impaired lacrimal function. The volunteers and patients underwent MRI with a single-shot spin-echo echo-planar technique using a 47-mm microscopy coil. The apparent diffusion coefficient (ADC) of the lacrimal and parotid glands was obtained with b factors of 500 and 1,000 sec/mm(2). T1-weighted and fat-suppressed T2-weighted MR microscopic images were also obtained to evaluate the gland morphology and signals. RESULTS: MR microscopy provided high-resolution images of the lacrimal glands that enabled ADC measurements. The ADCs of the normal lacrimal glands showed no significant sex- or age-related changes. The ADCs for the lacrimal glands were significantly higher than those of the parotid glands in the same subjects (mean +/- SD, 891 +/- 103 vs 703 +/- 84 x 10(-6) mm(2)/sec, respectively; p < 0.0001, Mann-Whitney U test). We found that ADCs of the lacrimal glands in Sjogren's syndrome patients were significantly lower than those from the normal glands of age-matched healthy volunteers (736 +/- 34 vs 923 +/- 84 x 10(-6) mm(2)/sec; p < 0.0001, Mann-Whitney U test). CONCLUSION: These findings suggest that the measurement of ADCs may be a useful tool to assess abnormalities of the lacrimal glands in patients with Sjogren's syndrome.