Nihon Hoshasen Gijutsu Gakkai zasshi最新文献

Purpose: We investigated flip angle (FA) and cerebrovascular imaging performance in three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA) without using a venous signal saturation pulse in the diagnosis of acute cerebral infarction.

Methods: 3D TOF-MRA was performed in healthy volunteers at FAs of 9°-21° without using a venous signal saturation pulse. The contrast of cerebral arteries, veins, and parenchyma was measured, and the visualization of blood vessels was compared by visual evaluation.

Results: Cerebral artery contrast was highest at a 19° FA, and the visual evaluation also showed the highest rated results at a 19° FA. The cerebral venous contrast did not depend on the FA, and it was almost constant.

Conclusion: A repetition time of 10 ms and a 19° FA are the optimal settings for 3D TOF-MRA without using a venous signal saturation pulse, which reduces the imaging time by approximately 60% compared to the conventional method.

Purpose: In radiation therapy, the absorbed dose is corrected for changes in the nominal treatment distance using the inverse square law. However, in the case of electron beams, the inverse square law using the nominal treatment distance is invalid. Therefore, an effective source-to-surface distance (SSD) should be determined. The effective SSD must be measured for all electron beam energies and applicator sizes. Here, we calculated the effective SSD using a radiotherapy planning system with an electron Monte Carlo (eMC) calculation algorithm and evaluated its usefulness.

Methods: The effective SSD was calculated from the absorbed dose ratio at d_max at extended SSDs under 5 gap conditions, using both eMC calculations and LINAC measurements. The consistency between calculated and measured values was evaluated based on the absorbed dose ratio at d_max, effective SSD, and distance correction factor.

Results: The difference in the absorbed dose ratio at d_max between eMC calculations and measurements at extended SSDs was within 1.38%, and the effective SSD values agreed within 5.40 cm. Larger discrepancies in effective SSD were observed under conditions of high energy with large field sizes and low energy with small field sizes.

Conclusion: The good agreement in absorbed dose ratio at d_max, effective SSD, and distance correction factor between eMC calculations and measurements indicates that effective SSD calculation using eMC is feasible and can be employed for comparative verification against measured values.

Purpose: The objective of this study is to achieve site-specific three-dimensional (3D) automatic segmentation of skeletal muscles in body CT images. We aimed to improve recognition accuracy of nine muscle regions: sternocleidomastoid, erector spinae, trapezius, supraspinatus, rectus abdominis, obliques, quadratus lumborum, psoas major, and iliacus. Then, we focused on utilizing all skeletal muscle areas outside the target recognition regions that were not previously used.

Methods: Our method trains the 2D U-Net to learn both the target site-specific skeletal muscle region and all other skeletal muscles together. We utilized 30 cases of unenhanced body CT images and performed three-fold cross-validation.

Results: The proposed method achieved an average Dice coefficient of 88.37% across nine regions, showing improvements of 25.78% and 1.86% compared to the individual learning of each region (baseline) and the simultaneous learning of erector spinae (previous method), respectively.

Conclusion: Comprehensive learning of all skeletal muscle regions successfully improved the accuracy of U-Net-based 3D automatic segmentation for site-specific skeletal muscles in body CT. It leads to enhanced, precise body composition analysis for skeletal muscle regions.