Purpose

　The assessment of bone foramina is essential for evaluating surgical results after ACL reconstruction. Typically, CT scans are used to evaluate bone tunnels, whereas 3D MRI images are rarely used for evaluation. Therefore, the purpose of this study was to use MRI to verify whether surface renderings created using the image processing software installed in the MRI system were useful for evaluating femoral bone tunnels without using workstation software.

Method

　To determine the optimal 3D sequence parameters for evaluating bone tunnels, we created 3D images of 20 male and 20 female patients, aged 15-56 years who underwent ACL reconstruction surgery and evaluated the images using the quadrant method. We compared CT and MRI using the quadrant method to determine whether MRI can be used to evaluate bone tunnels.

Conclusion

　Calculation of concordance rates among kappa coefficients of MRI and CT images for the position coordinates and foramina diameters obtained by the quadrant method determined kappa coefficients which were ≥0.87. Accordingly, MRI using surface rendering is a useful imaging method without exposure to radiation as an alternative to CT for bone hole evaluation after ACL reconstruction.

Purpose : Residual aliasing artifacts are often generated in MR images acquired using parallel imaging (PI) and/or echo-planar imaging (EPI). Existing denoising methods based on convolutional neural networks (CNNs) assume that an image has spatial locality. Since the artifacts do not satisfy the assumption of CNNs, denoising methods based on CNNs cannot remove artifacts efficiently. In this presentation, the author proposes a new method that can significantly reduce residual aliasing artifacts. The proposed method utilizes the locations of aliasing artifacts and/or N-half ghost artifacts, which can be analytically calculated.

Methods : CNNs based on ResNet, with and without aliasing layers (ALs), were used to remove artifacts from the reconstructed MR images. For training and testing the CNNs, 31 fluid-attenuated inversion recovery (FLAIR) images (30 training, 1 testing) were used. PI aliasing artifacts were simulated by adding noise to the k-space. In the case of EPI, even and odd encodes in k-space were shifted to simulate aliasing artifacts.

Results : The use of ALs significantly reduced training and validation errors. The CNN without ALs suppressed the brain structures where signals were weak. In contrast, the correction method using CNNs with the proposed ALs suppressed parallel imaging aliasing and EPI ghosting artifacts, selectively.

Conclusion : The correction method using the proposed AL could effectively remove PI aliasing and EPI ghosting artifacts.

　We analyzed changes in apparent diffusion coefficient (ADC) during the cardiac cycle of the brain using bulk-motion-compensated diffusion imaging. ADC changes during the cardiac cycle were predominantly caused by water molecule fluctuations due to brain pulsation rather than the bulk motion of the brain parenchyma.

　According to the view that cerebrospinal fluid (CSF) and ISF exchange dynamically and form a pathway to remove waste products from the brain, CSF is likely to contain a high concentration of waste products. Based on recent results of T2 analyses, CSF seems to contain low protein, suggesting that this might not be the case.

　In this study, we evaluated the association between time-dependent apparent diffusion coefficient (ADC) at different diffusion times and histopathological features, such as the cellular area in a tumor and Ki-67 labeling index, in two breast cancer xenograft models. The ADC values decreased with diffusion time (from 2 ms to 27.6 ms). ADC change can be a more useful quantitative parameter than single ADC measures for estimating detailed pathological features, and it might also reflect tumor proliferation.

　Sarcopenia, a condition characterized bedridden skeletal muscle atrophy, is frequently encountered in today's aging society, in which healthy living needs to be improved.

　Skeletal muscle cells are composed of slow and fast twitch muscle fibers, and it is known that fast twitch fibers change to slow twitch ones with age. However, there is no way to capture the changes in which fast twitch slows down in clinical research.

　Slow twitch muscle fibers are known to have larger cells than fast twitch ones; however, in recent years, a muscle cell visualization method using these differences in muscle cell size has been reported using qsi. In this study, we captured age-related muscular atrophy with q-space imaging and explored the possibility of a quantitative evaluation by observing its transition.

　This study was approved by the Keio University School of Medicine's Ethics Committee. It included a total of 24 people (16 men and 8 women, with a mean age 56.1±14.7 years) who gave their informed consent. We used a 3T MRI (Siemens) machine to obtain horizontal magnetic resonance images at a certain level (L3/4).

　T2WI and DWI were imaged in the b-value range of 0 to 4000 (mm²/s). The muscle cross-sectional area was measured from the obtained T2WI, and q-space analysis was performed using DWI to calculate HWHM, KT, and ZP. In addition, the ADC values were measured using DWI. Pearson's product-moment correlation coefficients between these image parameters and age were calculated.

　The qsi metrics showed a superior correlation. This shows that the amount of displacement of water molecules changes in the elderly, and the possibility qsi analysis is useful for the diagnosis of quantitative sarcopenia.

　It is necessary to measure the rate of transition of muscle fibers such as slow and fast twitch fibers, and histological changes such as those that occur in fibers due to sarcopenia, and to validate it by combining clinical, histological, and MRI findings in the future.

　The purpose of this study was to detect free radical generation induced by X-ray irradiation using dynamic nuclear polarization (DNP)-MRI. The Electron Spin Resonance (ESR) signal intensity of the capillary, including that of Tempol and glutathione (GSH), decreased after X-ray radiation therapy. The reduction in the Tempol radical was dependent on the irradiation dose. The gel phantom, including Tempol, GSH, and 1% agarose, were clearly visualized radiation dose and trajectory using DNP-MRI. These results suggest that the DNP-MRI/Tempol gel method might be a useful technique for the visualization of X-ray irradiation.