Nihon Hoshasen Gijutsu Gakkai zasshi最新文献

Purpose: The purpose of this study was to perform auto-segmentation on cases in the head and neck region and to elucidate the characteristics of the extraction performance.

Methods: Auto-segmentation was performed on 100 cases in the head and neck region in Japan. The Auto-segmentation contours were compared with the clinical contours. The evaluation structures were the brain, brainstem, spinal cord, mandible, parotid gland, larynx, and eyeballs. DSC and HD were used for similarity evaluation.

Results: Overall, there was a high similarity in the eyeball and spinal cord. However, the lower the contrast with neighboring objects and the greater the variation in shape, the lower the similarity. In addition, metal artifacts lowered the similarity in some areas.

Conclusion: When auto-segmentation extraction was performed, differences were observed in the degree of similarity between organs. Depending on the case and morphology, the accuracy of auto-segmentation extraction varied from site to site, even for the same organ. The characteristics of the extractability found in this study make it useful for the manual modification of contouring.

Purpose: This study aimed to clarify the effects of radiopharmaceuticals and buffer solutions on the accuracy of the Hoffman phantom examination.

Methods: The Hoffman phantom was prepared using the water immersion method and was injected with 3 different solutions: ¹²³I-MIBG, ¹²³I-IMP only, and ¹²³I-IMP plus buffer solution. Single photon emission computed tomography (SPECT) / computed tomography (CT) imaging was performed at 3-time points: immediately after encapsulation, after 10 min of stirring, and after 20 min of stirring. The relative SPECT counts and left-right ratios of the images obtained under each condition were evaluated.

Results: The results revealed that the buffer solution facilitated the mixing of ¹²³I-IMP, affecting the initial distribution of the radiopharmaceutical. However, after 20 min of stirring, no significant differences were observed in the relative SPECT counts and the left-right ratio of SPECT images among the different solutions, regardless of the radiopharmaceutical type or the presence of the buffer, in most regions.

Conclusion: Buffer solution promotes the mixing process; however, it was confirmed that sufficient agitation alone can produce comparable SPECT images, indicating that the use of a buffer may not be necessary if proper agitation is ensured during phantom preparation.

Purpose: In DRLs 2020, in addition to the fluoroscopic dose rate, air kerma at the patient entrance reference point (K_a,r) and air kerma-area product (P_KA) by types of medical treatment and diseases were set as DRL quantity. We surveyed the current equipment setting dose at each facility and the exposure dose in clinical practice. We considered the optimal DRL classification of K_a,r and P_KA for the next DRLs update.

Methods: We conducted a questionnaire survey of 428 facilities in Japan with angiography devices and analyzed the obtained angiography dose data.

Results: Fluoroscopic dose rate, K_a,r, and P_KA were lower values compared to past studies and DRLs 2020 data, and significant differences were observed in K_a,r and P_KA by procedure.

Conclusion: Equipment setting doses have been optimized at each facility, and it is expected that radiological protection will be optimized by setting DRL values that reflect the current situation.

Purpose: There are attempts to assess tumor heterogeneity by texture analysis. However, the ordered subsets-expectation maximization (OSEM) reconstruction method has problems depicting heterogeneities. The aim of this study was to identify image reconstruction parameters that improve the ability to depict internal tumor necrosis using a self-made phantom that simulates internal necrosis.

Methods: Self-made phantoms were prepared using polypropylene cylinders with inner diameters of 18.0 mm and 6.0 mm. The concentration ratios of the simulated tumor : tumor interior were 4 : 0 and 4 : 1. For each reconstruction method, the iteration for OSEM and OSEM+point spread function (PSF) were 1 to 25 and the subset was 12. The β values for block sequential regularized expectation maximization (BSREM) were set between 10 and 400. We evaluated the features of the profile curve, contrast-to-noise ratio, and grey-level co-occurrence matrix (GLCM).

Results: In the phantom study, OSEM and OSEM+PSF showed a better delineation of the differences between the inside and outside of the cylinder as iteration was increased and BSREM showed a better delineation as β was decreased. The highest value for each feature, both 4 : 0 and 4 : 1, was BSREM β 10 for angular second moment (ASM) and inverse differential moment (IDM), OSEM iteration 25 for contrast and entropy.

Conclusion: We have identified image reconstruction parameters that improve the ability to visualize internal tumor necrosis. The parameter was BRSEM β 10.

Purpose: To investigate the accuracy of proton density fat fraction (PDFF) measurement using chemical shift-encoded MRI (CSE-MRI) with fast imaging techniques in a phantom.

Methods: A 1.5T imaging system (Prodiva; Philips Healthcare) and PDFF phantom (Fat Fraction Phantom Model 300; Calimetrix) were used in this study. The acquisitions without fast imaging techniques (conventional acquisition), with parallel imaging in phase-encode direction (SENSE acquisition), with compressed sensing (CS-SENSE acquisition), and with parallel imaging in both phase-encode and slice-encode direction (Dual-SENSE acquisition) were performed. The following acceleration factors in SENSE and CS-SENSE acquisition were used: 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0. For Dual-SENSE acquisition, the same acceleration factors (1.5, 2.0, 3.0, 4.0, 5.0) were set in each of the two directions. The relationships between reference PDFF values and PDFF measurements obtained using each acquisition were assessed using linear regression analysis and Bland-Altman analysis.

Results: According to the linear regression analysis, the slopes and intercepts of regression lines were from 0.87 to 1.02 and from 0.06% to 3.55%, respectively. According to Bland-Altman analysis, there were fixed bias between reference PDFF values and PDFF measurements obtained using SENSE acquisition with reduction factor 8.0 and Dual-SENSE acquisition with reduction factor 5.0. For CS-SENSE acquisition with reduction factor from 7.0 to 8.0, SENSE acquisition with reduction factor from 3.0 to 8.0, and Dual-SENSE acquisition with reduction factor from 2.0 to 5.0, some vials had ±1.5% or more errors between the reference PDFF values and PDFF measurements in the range of 0% to 50% PDFF.

Conclusion: In CS-SENSE acquisition, the accuracy of PDFF measurement was maintained within 1.5% up to a reduction factor 6.0. The accuracy of PDFF measurement was maintained within 1.5% up to a reduction factor 2.0 in SENSE acquisition and a reduction factor 1.5 in Dual-SENSE acquisition.

Purpose: The purpose of this study was to propose a method for measuring the maximum leaf velocity (V_max) of the multileaf collimator (MLC) in a dynamic MLC irradiation.

Methods: The irradiation was carried out with a plan in which the MLC leaves were constantly and gradually accelerated. Based on this plan, it was assumed that the velocity of each leaf v(t) (t is the elapsed time) would initially increase but plateau once it reached its maximum velocity. In the proposed method, v(t) was calculated from the log file data during irradiation, and fitted by a piecewise linear function consisting of 2 linear segments (constant acceleration and constant velocity segments); V_max was determined as the velocity in the constant velocity segments. The V_max values in each accelerator were obtained periodically for 7 months (20 measurements in total).

Results: In all measurements, the constant acceleration and constant velocity segments in v(t) were clearly distinguished by the piecewise linear approximation, and the V_max was determined. The mean V_max value of each leaf ranged from 3.63 to 4.32 cm/s with standard deviations (SD) less than 0.04 cm/s.

Conclusion: The proposed method made it possible to confirm the long-term stability of the V_max easily.

Purpose: Hereditary breast and ovarian cancers (HBOC) carry a high risk of breast cancer, and detailed screening with contrast-enhanced breast MRI (breast MRI surveillance) is recommended. With the increase in the number of individuals diagnosed with HBOC, the demand for breast MRI surveillance is also rising. However, the current system is inadequate, with factors such as lack of knowledge and indifference among healthcare professionals, and insufficient understanding of breast MRI surveillance being cited. This study aims to investigate the knowledge of HBOC and the awareness of breast MRI surveillance among radiological technologists, and to analyze the factors that promote these practices.

Methods: A web-based survey was conducted among radiological technologists at 1278 facilities with MRI installations.

Results: Responses were obtained from 433 individuals. The knowledge of HBOC was insufficient, with 49.6% unaware that breast MRI surveillance is recommended. Factors promoting awareness included the amount of knowledge about HBOC, age, and the presence of MRI specialists and mammography screening specialists.

Conclusion: By enhancing the acquisition of knowledge about HBOC and raising awareness of breast MRI surveillance, it is expected that discussions towards building a robust system will deepen.