Nihon Hoshasen Gijutsu Gakkai zasshi最新文献

Purpose: This study aimed to evaluate the influence of the scanning speed of whole-body scans on the detectability of positive vertebral bone images in bone scintigraphy.

Methods: We used SIM² bone phantom to obtain planar images equivalent to scanning speeds of 15, 17, and 20 cm/min. Receiver operating characteristic (ROC) analysis to evaluate lesion detectability and average count (Ct)/pixel, contrast ratio, and contrast-to-noise ratio (CNR) of the normal vertebral body and the simulated tumor site were measured.

Results: The average area under the ROC curves (AUC) was 0.936, 0.929, and 0.915 at speeds of 15, 17, and 20 cm/min, respectively. The average AUC at 20 cm/min was significantly lower than that at 15 cm/min (p<0.05) . However, no other significant differences were found (p=0.448, 0.139). The average Ct/pixel and CNR decreased at 15, 17, and 20 cm/min. The contrast ratio did not change.

Conclusion: The results showed that increasing the scan speed from 15 cm/min to 17 cm/min had no effect on the detection of vertebral lesions. Thus, it is possible to reduce the scan time, albeit slightly.

Purpose: To evaluate the robustness of the latest periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technology from each vendor against head movements and to investigate their characteristics for effective clinical use.

Methods: Using a phantom simulating the T2-weighted image of the human brain, images were acquired with devices from CANON MEDICAL SYSTEMS (Tochigi, Japan; hereinafter "Canon"), GE HealthCare (Chicago, IL, USA; hereinafter "GE"), Philips (Amsterdam, Netherlands), and Siemens Healthineers (Forchheim, Germany; hereinafter "SIEMENS"). The head motion patterns were divided into rotation angle dependency (single rotation and multiple rotations) and rotation frequency dependency and evaluated using structural similarity (SSIM).

Results: For rotation angle dependency, Canon was robust against small rotation angles and fine movements. Despite the rotation angle, GE was robust against movements, with deep learning reconstruction (DLR) improving correction functionality. Philips could be used with compressed sensitivity encoding (CS), and robustness varied with blade width. SIEMENS was robust against large movements. For rotation frequency dependency, results were similar across the 4 vendors.

Conclusion: The rotation angle and rotation frequency dependencies of the PROPELLER technology from the 4 vendors were quantitatively evaluated. Understanding the characteristics of PROPELLER allows for the possibility of providing diagnostic-quality images even for patients who move during head MRI exams by appropriately using PROPELLER.

Purpose: We evaluated the measurement accuracy and time efficiency of the tumor respiratory motion evaluation methods using a dynamic thorax motion phantom.

Methods: A total of 12 patterns of 4DCT images with different tumor displacements and artifacts were used for the measurement. Three methods were employed to measure tumor motion. The first method was the manual delineation of the tumor on each phase CT image with a treatment planning system (RTPS [Manual]). The second method was the automatic delineation of the tumor structure by deformation and copying (RTPS [Auto]). The third method was tumor motion analysis software (Simple 4D Analysis Ver.1.3.1 [Simple 4D]; Triangle Products, Chiba, Japan). For each method, the difference between the phantom motion and the measured value was determined.

Results: The differences (mean±standard deviation: SD) in the superior-inferior direction for RTPS (Manual), RTPS (Auto), and Simple 4D in the without-artifact images were -0.6 mm±0.6 mm, -5.0 mm±2.2 mm, and -1.0 mm±0.0 mm, respectively. The difference in the left-right and anterior-posterior directions was within 1 mm for all methods. Furthermore, the time required for Simple 4D was shorter than for the other methods.

Conclusion: Simple 4D showed the comparable measurement accuracy and improvement time efficiency to RTPS (Manual) and RTPS (Auto), and was useful for tumor respiratory motion analysis.

Purpose: To validate the effects of subject position on single energy metal artifact reduction (SEMAR) of a reverse shoulder prosthesis using computed tomography (CT).

Methods: A water phantom with a reverse shoulder prosthesis was scanned at four positions on the XY plane of the CT gantry (on-center, 50 mm, 100 mm, and 150 mm from on-center in the negative direction of the X axis, respectively). We obtained images with and without SEMAR. The artifact index (AI) was measured via physical assessment. Scheffé's (Ura) paired comparison methods were performed with the amount of metal artifact by ten radiological technologists via visual assessment.

Results: The AI was significantly reduced when using SEMAR. As the phantom moved away from the on-center position, the AI increased, and metal artifacts increased in Scheffé's methods.

Conclusion: SEMAR reduces metal artifacts of a reverse shoulder prosthesis, but metal artifacts may increase as the subject position moves away from the on-center position.

Purpose: Cerebral CT perfusion (CTP) summary maps classify the ischemic core, penumbra, and normal tissue from traditional parametric maps, which is a criterion for indicating thrombectomy. Since perfusion maps change when the CTP radiation dose is reduced, summary maps also might change. This study aimed to assess the noise characteristics of a summary map in simulation experiments.

Methods: We added various amounts of noise to a digital phantom and clinical CTPs, used Vitrea (Canon Medical Systems, Tochigi, Japan) to perform perfusion analysis, and assessed the relationship between the noise and cerebral blood volume (CBV), time to maximum (Tmax), and ischemic core and penumbra volumes.

Results: As the noise increased, the obtained CBV increased, the obtained Tmax shortened, and the obtained ischemic core and penumbra volumes decreased, which depended on the tissue's CBV and Tmax.

Conclusion: Under low-dose conditions, the ischemic core and penumbra volumes decreased, so the criteria for thrombectomy may differ from those for standard doses.

We investigated the impact of the tumor-to-normal bone ratio (TNR) on the concordance rate between a detectability score classified by software (DS_soft) using an automatic quantification package for bone SPECT (Hone Graph) and a detectability score classified by visual assessment (DS_visual), and considered the feasibility of applying this software to various TNR images. ^99mTc solution was filled into a SIM² bone phantom to achieve TNRs of 4, 6, and 8, performed by dynamic SPECT acquisitions performed for 12 minutes; reconstructions were performed using ordered subset expectation maximization at timepoints ranging from 4 to 12 minutes. This yielded a total of 384 lesions (96 SPECT images). We investigated the weighted kappa (κ_w) coefficient between DS_soft and DS_visual at various TNRs and evaluated the change in analysis accuracy before and after applying newly created analysis parameters. DSs were defined on a 4-point scale (4: excellent, 3: adequate, 2: average, 1: poor), and visual evaluations were conducted by three board-certified nuclear medicine technologists. The κ_w coefficients between DS_soft and DS_visual were 0.75, 0.97, and 0.93 for TNRs 4, 6, and 8, respectively, with each κ_w coefficient being significant (p<0.01). In the TNR 4 image group, κ_w coefficients significantly increased with the implementation of new parameters proposed in this study. We concluded that the software's automatic analysis would be closer to a visual assessment within the TNR range of 4-8 and that applying new parameters derived from this study to images with TNR 4 further improves the software's automatic analysis accuracy of DS_soft. We suggest that software will be a useful tool for optimizing bone SPECT imaging techniques.

Purpose: In DRLs 2020, the entrance surface air kerma (Ka,e) was set to 17 mGy/min as the reference dose rate in fluoroscopy. But, Ka,e in fluoroscopy for different regions and Ka,e in exposure was not set. A multicenter survey was conducted to evaluate Ka,e by each area.

Methods: Ka,e for each area was analyzed for 79 facilities attending this survey (274 machines and 461 protocols). When the protocols were changed by the difference in disease, angiography, or IVR, the difference rate of Ka,e was evaluated. Ka,e before and after modifying the incident air kerma at the patient entrance reference point (Ka,r) and air kerma area product (P_KA) difference rate were calculated when protocols were changed, considering the DRLs 2020.

Results: There were dose differences in Ka,e by each area. Compared to DRLs 2020, 36 protocols from 13 facilities modified their protocols, all of which reduced Ka,e.

Conclusion: Although reducing Ka,e does not necessarily reduce Ka,r, and P_KA, comparison of Ka,e by each area is expected to optimize medical exposure protection, including evaluation of quality control.

Purpose: To investigate the effect of different source dwell positions on dose distribution in the treatment of cervical cancer with brachytherapy.

Methods: Treatment planning data for cervical cancer patients were used. Treatment plans were created at 1 mm intervals, varying up to 5 mm. For intracavitary brachytherapy and intracavitary and interstitial brachytherapy, the following dose parameters were evaluated: 90% high-risk clinical target volume (HR-CTV D_90%), rectum 2 cm³ dose (Rectum D_{2 cc}), small intestine 2 cm³ dose (Small D_{2 cc}), sigmoid colon 2 cm³ dose (Sigmoid D_{2 cc}), bladder 2 cm³ dose (Bladder D_{2 cc}), point A dose.

Results: In intracavitary brachytherapy, the HR-CTV D_90%, Rectum D_{2 cc}, Small D_{2 cc}, and Sigmoid D_{2 cc} doses increased as the source dwell position changed in the direction. On the other hand, the dose of Bladder D_{2 cc} increased when the source position changed in the outward direction. The same trend was observed in the case of intracavitary and interstitial brachytherapy.

Conclusion: It was shown that a 1 mm change in the source dwell position can affect the dose by up to 2% or more. The accuracy of the source dwell position is very important and should be checked before using the device.

Purpose: We investigated whether peripheral pulse synchronization (PPUS) can be an alternate method for electrocardiographic synchronization (ECGS) in measuring myocardial T1 values in cardiac magnetic resonance imaging (CMRI).

Methods: T1 map imaging was performed on 49 patients undergoing CMRI using the 5s (3s) 3s modified Look-Locker inversion recovery (MOLLI) method for both ECGS and PPUS. The short-axis images of basal, mid, and apical segments were obtained. The T1 map images were analyzed using an image processing system, and T1 values were obtained for each cardiac segment. To assess the degree of agreement between T1 values obtained from ECGS and PPUS, the Bland-Altman analysis and the estimating intraclass correlation coefficient (ICC) were performed for the average T1 value of the entire myocardium and T1 values of each cardiac segment. Also, to evaluate whether PPUS imaging is possible in the diastole phase, we measured the length of systole in the electrocardiogram and the length of transmission (R-R') from R in the electrocardiogram to R (R') in the pulse waveform.

Results: From the comparison of T1 values, a good agreement of ICC was confirmed between the ECGS and PPUS (whole myocardium: 0.97, apical: 0.93, mid: 0.98, and basal: 0.97). The results of the Bland-Altman analysis also indicated good agreement. Moreover, it was shown that the heart was imaged in the diastole phase even with the default scan parameters of PPUS.

Conclusion: Our results indicated that PPUS can be an alternate method for ECGS.

Purpose: In this study, we evaluated image quality and radiation dose reduction when a Copper (Cu) filter was added to hip joint X-ray imaging.

Methods: We measured effective energy without (0 mm) and with (0.1/0.2 mm) Cu-added filter at 70 kV, and we calculated soft tissue-bone contrast and signal-difference-to-noise-ratio (SDNR) under constant entrance surface dose. After that, we estimated the dose reduction rate.

Results: The effective energy was 32.07 keV for 0 mm Cu, 37.59 keV for 0.1 mm Cu, and 40.91 keV for 0.2 mm Cu. As the thickness of the Cu-added filter was increased, contrast decreased, but SDNR increased. The dose reduction rate in bone calculated measuring SDNR was 34% for 0.1 mm Cu and 47% for 0.2 mm Cu in max.

Conclusion: It was suggested that adding Cu filter to hip-joint X-ray imaging could reduce entrance surface dose while maintaining the image quality based on SDNR.