Gunma Prefectural College of Health Sciences

BackgroundSecondary‐radiation background (BG) generated in kilovoltage X‐ray flat‐panel detectors (FPDs) under scanning proton beam irradiation has not been thoroughly analyzed.PurposeThis study aimed to determine and mathematically model the characteristics of secondary‐radiation BG in FPDs under scanning proton beam irradiation.MethodsUsing a synchrotron‐based proton system and two FPDs mounted on a gantry tilted at 135° to the proton beam axis, we acquired images of two phantoms (block and thorax). The FPD images were captured during three conditions: only X‐ray exposure, proton irradiation, and pauses between proton irradiations. Because the FPD readout rate (30 fps) was twice the X‐ray exposure rate (15 pps), the images were further categorized into two types: those corresponding to with and without X‐ray exposure. These FPD images were analyzed to determine the characteristics of the secondary‐radiation BG. In addition, a Monte Carlo simulation was conducted to complement the performed measurements.ResultsAnalysis of the FPD images without X‐ray exposure revealed that the pure secondary‐radiation BG appeared as sparse spike patterns without a noticeable spatial bias across the FPD area in most images. The BG affected only 1.25% of the FPD pixels and could be modeled as an exponentially decreasing function with increasing pixel intensity. When considering typical X‐ray image brightness for the block and thorax phantoms, the impact of the BG on mean‐pixel‐intensity variation was < 1%. Monte Carlo simulations suggested that prompt photons were the primary source reaching the FPD.ConclusionsThis study demonstrates that the secondary‐radiation BG characteristics observed in the X‐ray FPD images during scanning proton beam irradiation can be quantitatively modeled. The impact of the secondary‐radiation BG on mean‐pixel‐intensity of FPD images was minimal.

Abstract Objective: To elucidate the anatomical characteristics and three-dimensional continuity of a previously unrecognized thin adipose compartment between the colonic mesentery and retroperitoneum, using correlative microscopy and block-face imaging (CoMBI). Summary Background Data: The interface between the colonic mesentery and retroperitoneum has traditionally been considered a fusion fascia (e.g., Toldt’s fascia). However, emerging evidence suggests more complex fascial remodeling, with previous studies lacking comprehensive spatial context. Methods: Seven adult cadavers were examined. Histological analysis was conducted on six specimens using paraffin sections stained with Elastica van Gieson and Masson’s trichrome. One cadaver underwent three-dimensional morphological analysis using CoMBI. Serial block-face images of the perirenal region were captured at 100 μm intervals, and three-dimensional reconstruction segmentation was performed. Results: A distinct thin adipose compartment (0.3–2.0 mm thick) was consistently observed between the colonic mesentery and perirenal fat, enclosed by dense connective tissue and containing small vessels. Similar compartments were also found between the perirenal fat and pararenal fat, and beneath the peritoneum along the abdominal wall. These compartments extended in three directions from the peritoneal reflection and demonstrated craniocaudal continuity, laterally, these form a triad-like junction. Conclusions: The thin adipose compartment represents a structurally organized anatomical unit rather than amorphous filler. Its consistent continuity and integration with adjacent structures support a compartment-based framework of intra-abdominal anatomy, with implications for surgical navigation.

The PET Imaging Site Qualification Program for amyloid positron emission tomography (PET) in Japan includes visual evaluation of the cylinder phantom. This visual evaluation requires observation of the entire image of the phantom and confirmation of the absence of apparent artifacts. Because the evaluation is visually performed, inter-observer differences might exist among evaluators for difficult cases. Therefore, the workload of the staff who perform approval tasks must be reduced, and objective evaluation methods are needed. Thus, we attempted to develop an artificial-intelligence-based objective method for anomaly detection. Three artificial intelligence methods for anomaly detection were developed, and their accuracy was evaluated using AutoEncoder, AnoGAN, and a method combining feature extraction using AlexNet and a one-class support vector machine. In total, 10,207 normal images from 128 facilities and 594 abnormal images from eight facilities, all of which were submitted as part of application for amyloid PET certification, were used. Group five-fold cross-validation was employed for artificial intelligence training and evaluation. In addition, the performance of each artificial intelligence method was assessed using receiver operating characteristic analysis. The areas under the curve for anomaly detection using AutoEncoder, AnoGAN, and the method combining feature extraction using AlexNet and a one-class support vector machine were 0.80 ± 0.04, 0.77 ± 0.03, and 0.99 ± 0.01, respectively. Artificial intelligence effectively distinguished between normal and abnormal images with high accuracy. In the future, its practical implementation is anticipated to reduce the workload in the approval work for the Japanese site qualification program for amyloid PET.

Evaluating prostate MRI resolution is challenging due to motion artifacts caused by body movement or intestinal gas, which can degrade image quality. One simple approach to resolution assessment is the ladder method, but reports of its application to clinical images remain limited. This study aimed to compare the ladder method with visual evaluation to assess its utility. T2-weighted images of the prostate in healthy volunteers and a ladder phantom at various resolutions with altered pixel sizes (0.5, 0.7, 0.9 and 1.1 mm) were acquired. Three radiologists conducted visual evaluations of the prostate images. Correlation coefficients between the visual evaluation scores and the ladder index(LI) obtained from the ladder method were compared. Average visual evaluation scores were 7.7, 5.9, 3.8, and 2.1, while the spatial frequencies corresponding to LI = 0.5 (50%LI) were 0.86, 0.81, 0.54, and 0.42 cycles/mm for each pixel size ranging from 0.5 to 1.1 mm, demonstrating higher values at smaller pixel sizes. The correlation coefficients exceeded 0.7 at most spatial frequencies, indicating a strong correlation. Inter-reader agreement was high (Kendall's W = 0.87), indicating consistent evaluation among radiologists. Spatial resolution for prostate MRI could be evaluated objectively using the ladder method.

Introduction: White matter hyperintensity (WMH) is associated with cognitive impairment, although the clinical significance of WMH remains unclear. We aimed to elucidate the clinical significance of WMH volume and whether a fully automated quantitative analysis of WMH would be an effective marker of cognitive function. Methods: Patients with suspected cognitive impairment were retrospectively examined. Clinical data, including patient information, neuropsychological examinations, diagnoses of dementia disorders, and fluid-attenuated inversion recovery (FLAIR) images, were collected. Patient information included sex, age, and educational level. Neuropsychological examinations included the Mini-Mental State Examination (MMSE) and Japanese version of the Montreal Cognitive Assessment (MoCA-J). WMH volumes were analyzed from FLAIR images using a fully automatic analysis software. The relationship between WMH volume and clinical data was investigated. Results: WMH volume was analyzed using 889 FLAIR cases. The WMH volume did not differ significantly between the sexes. WMH volume showed a positive correlation with age. Multiple comparison tests showed no significant difference in WMH volume between junior high school and high school graduates, but all other differences were significant. Multiple comparison tests revealed significant differences in mean WMH volume among all groups in the classified MMSE. The Mann-Whitney U test revealed significant differences in WMH volume between the two groups. Multiple comparison tests revealed significant differences in WMH volume among all the groups of classified diagnostic results. Conclusion: Quantitative analysis of WMH volume from FLAIR images may provide useful information for dementia treatment and may be effective as a new marker in cognitive function examinations.

Introduction. Monte Carlo simulation codes simulating medical imaging nuclear detectors (SIMIND) are notable tools used to model nuclear medicine experiments.This study aimed to confirm the usability of SIMIND as an alternative method for nuclear medicine experiments with a cardiac phantom HL, simulating human body structures, by comparing the actual experiment data.Methods. A cardiac phantom HL that simulates myocardial scintigraphy using123I-meta-iodobenzylguanidine was developed, and single-photon emission computed tomography/computed tomography imaging was performed using Discovery NM/CT 670 scanner. Aside from the main-energy window(159 keV ± 10%), additional windows were set on the low(137.5 keV ± 4% ) and high(180.5 keV ± 3%)-energy sides. The simulations were performed under the same conditions as the actual experiments. Regions of interest (ROIs) were set in each organ part of the experiments and simulated data, and a polar map for the myocardial part was developed. The mean, maximum (max), and minimum (min) counts within each ROI, as well as the relative errors of each segment in the polar map, were calculated to evaluate the accuracy of the simulation.Results. Overall, the results were favorable with relative errors of <10% except in some areas based on the data from the main-energy window and postreconstruction. On the other hand, relative errors of >10% were found in both the low and high subenergy windows. The smallest error occurred when assessing using mean values within the ROIs. The relative error was high at the cardiac base in the polar map evaluation; however, it remained <10% from the mid to apical heart sections.Conclusion. SIMIND is considered an alternative method for nuclear medicine experiments using a myocardial phantom HL that closely resembles human body structures. However, caution is warranted as accuracy may decrease under specific conditions.