Hiroshi Kunitomo

To investigate the spatial accuracy of delineating prostatic calcifications by quantitative susceptibility mapping (QSM) in comparison with computed tomography (CT), we conducted phantom and human studies. Five differently-sized spherical hydroxyapatites mimicking prostatic calcification (pseudo-calcification) were arranged in the order of their sizes at the center of a plastic container filled with gelatin. This calcification phantom underwent magnetic resonance (MR) imaging, including the multiple spoiled gradient-echo sequences (SPGR) for the QSM and CT as a reference. The volume of each pseudo-calcification and center-to-center distance between the pseudo-calcifications delineated by QSM and CT were measured. In the human study, eight patients with prostate cancer who underwent radiation therapy and had some prostatic calcifications were included. The patients underwent CT and SPGR and modified DIXON sequence for MR-only simulation. The hybrid QSM processing combined with the complex signals in the SPGR and water and fat fraction maps estimated from the modified DIXON sequence were used to reconstruct the pelvic susceptibility map in humans. The threshold of CT numbers was set at 130 HU, while the QSM images were manually segmented in the calcification phantom and human studies. In the phantom study, there was an excellent agreement in the pseudo-calcification volumes between QSM and CT (y = 1.02x - 7.38, R2  = 0.99). The signal profiles had similar trends in CT and QSM. The center-to-center distances between the pseudo-calcifications in the phantom were also identical in QSM and CT. The calcification volumes were almost identical between the QSM and CT in the human study (y = 0.95x - 9.32, R2  = 1.00). QSM can offer geometric and volumetric accuracies to delineate prostatic calcifications, similar to CT. The prostatic calcification delineated by QSM may facilitate image-guided radiotherapy in the MR-only simulation workflow.

BACKGROUND: R2* relaxometry analysis combined with quantitative susceptibility mapping (QSM), which has high sensitivity to iron deposition, can distinguish microstructural changes of the white matter (WM) and iron deposition, thereby providing a sensitive and biologically specific measure of the WM owing to the changes in myelin and its surrounding environment. This study aimed to explore the microstructural WM alterations associated with cognitive impairment in patients with Parkinson's disease (PD) using R2* relaxometry analysis combined with QSM. MATERIALS AND METHODS: We enrolled 24 patients with PD and mild cognitive impairment (PD-MCI), 22 patients with PD and normal cognition (PD-CN), and 19 age- and sex-matched healthy controls (HC). All participants underwent Montreal Cognitive Assessment (MoCA) and brain magnetic resonance imaging, including structural three-dimensional T1-weighted images and multiple spoiled gradient echo sequence (mGRE). The R2* and susceptibility maps were estimated from the multiple magnitude images of mGRE. The susceptibility maps were used for verifying iron deposition in the WM. The voxel-based R2* of the entire WM and its correlation with cognitive performance were analyzed. RESULTS: In the voxel-based group comparisons, the R2* in the PD-MCI group was lower in some WM regions, including the corpus callosum, than R2* in the PD-CN and HC groups. The mean susceptibility values in almost all brain regions were negative and close-to-zero values, indicating no detectable paramagnetic iron deposition in the WM of all subjects. There was a significant positive correlation between R2* and MoCA in some regions of the WM, mainly the corpus callosum and left hemisphere. CONCLUSION: R2* relaxometry analysis for WM microstructural changes provided further biologic insights on demyelination and changes in the surrounding environment, supported by the QSM results demonstrating no iron existence. This analysis highlighted the potential for the early evaluation of cognitive decline in patients with PD.

PURPOSE: To evaluate image quality for chest radiography at different radiation qualities, using phantoms with scatter fractions similar to those of lungs. METHODS: Two base phantoms with 10 and 4 cm thicknesses, respectively, made of a soft tissue-equivalent material, were used to mimic the X-ray attenuation of the human lung. Two plates with soft tissue- and bone-equivalent materials, respectively, were placed on the base phantom as contrast objects. The image data were obtained with the same entrance surface dose in each radiation quality. Six radiation qualities generated using 120 and 90 kV, and additional copper filters with thicknesses 0, 0.1, and 0.2 mm were selected. The signal-difference-to-noise ratio (SdNR) and a contrast ratio of the soft tissue to the bone were measured for the six radiation qualities. RESULTS: The thicker the additional filter, the better the SdNR at both tube voltages. The SdNR values were not significantly different between 120 and 90 kV for the same filter thickness. The contrast ratio was higher at 120 than at 90 kV by approximately 8%. CONCLUSIONS: Because of the advantage of the contrast ratio and the highest SdNR, the radiation quality with 120 kV and 0.2-mm copper filtration was the best. It was indicated that the conventional tube voltage of 120 kV remains to be better than the lower tube voltage of 90 kV.

Mammography equipment attached to the digital breast tomosynthesis (DBT) system is widespread in Japan. However, there are no guidelines for quality control methods for DBT in Japan. Therefore, it is necessary to rapidly establish a performance evaluation procedure and a quality control procedure for DBT. In this study, we conducted basic experiments using DBTs of five companies (Canon Medical, Fujifilm Medical, GE Healthcare, Hologic, Siemens) already sold in Japan and examined feasible common items. We aimed to establish a quality control method for DBT in Japan. The measurement was performed based on the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF) breast tomosynthesis quality control protocol, version 1.03. In this study, we tried to measure 18 items in DBT. We examined whether the 18 items could be measured using each device; it is not an evaluation of device performance based on the measured values. There were some management items that were difficult to implement due to the specifications of DBT, such as devices that required pressure on DBT operation, problems due to the shape of bucky, and devices that did not have stationary mode. There were also problems with measurement data; for example, devices could not retrieve projection data and reconstruction data. This study clarified points to be considered for establishing common quality control items. In the future, we will carefully refer to the recently published IEC 61223-3-6, consider international harmonization, and establish DBT guidelines customized for the Japanese market.

To clarify the temperature dependence of susceptibility estimated by quantitative susceptibility mapping (QSM) analysis, we investigated the relationship between temperature and susceptibility using a cylinder phantom with varying temperatures. Six solutions with various concentrations of superparamagnetic iron oxide (SPIO) nanoparticles were employed. These tubes were placed in a cylinder phantom and surrounded with water. The temperature of the circulated water was adjusted to change the temperature in the cylinder phantom from 25.8 °C to 42.5 °C. The cylinder phantom was scanned via a three-dimensional multiple spoiled gradient-echo sequence for R2* and QSM analyses with varying temperatures. The relationships between temperature, susceptibility, and R2* values were determined. Moreover, the temperature coefficients of susceptibility (χ-Tc) and (R2*-Tc) were calculated at each concentration and the linearities in these indices against each SPIO concentration were validated. Significant inverse correlations were found between temperature, susceptibility, and R2* values at each SPIO concentration due to the decrease in paramagnetic iron susceptibility that occurred with increasing temperature based on Curie's law. Moreover, although there were significant correlations between the susceptibility and R2* values at any temperature, the slopes of the regression lines grew in height with greater temperatures. The percentage of difference per Celsius degree in susceptibility in any SPIO concentration was lower than the corresponding finding among the R2* results. There were strong linearities between the SPIO concentration, χ-Tc (r = -0.994; p < 0.001), and R2*-Tc (r = -0.998; p < 0.001). The χ-Tc and R2*-Tc outcomes in a particular voxel varied considerably with the iron contents. Although there was an inverse correlation noted between temperature and susceptibility, the susceptibility analysis showed smaller temperature dependence relative to the R2* analysis. QSM analysis might be a more suitable option for magnetic resonance-based iron quantification in comparison with R2* relaxometry.