[The Study for Standardization of Dose Evaluation Method in Cone-beam CT]

PURPOSE

This study aimed to compare the dose evaluation methods by constructing simulation models using the Monte Carlo calculation code and propose an evaluation method for cone beam CT (CBCT) that ensures accuracy and practicality.

METHODS

The Particle and Heavy Ion Transport code System (PHITS) ver. 3.26 was used as the Monte Carlo calculation code. CBCT doses were measured by CB dose index (CBDI) and American Association of Physicists in Medicine task group 111 (TG111) methods. The CBDI was compared with the equilibrium doses obtained by the TG111 method.

RESULTS

Although CBDI was lower than equilibrium doses obtained by the TG111 method, its practicality was ensured because it can be measured using the dosimeter and phantom that are commonly used. In contrast, the TG111 method guarantees accuracy, but it is difficult to prepare a long phantom to obtain the equilibrium dose. The TG111 method with a phantom length of 15 cm underestimated the equilibrium dose by 20% compared to that with a phantom length of 45 cm that satisfies the dose equilibrium. Therefore, the equilibrium dose obtained by the TG111 method with a phantom length of 15 cm is multiplied by 1.20 to obtain the equilibrium dose equivalent to that with a phantom length of 45 cm.

CONCLUSION

This study has proposed the dose evaluation method that combines guarantees accuracy and practicality in CBCT.

Basic characteristics of Vision badge and its performance as an eye lens dosimeter for endoscopists

Vision badge is an eye lens dosimeter to measureHp(3). This study aimed to evaluate the basic characteristics of the Vision badge and its performance as an eye lens dosimeter for endoscopists by phantom study. Energy dependence was evaluated by changing the tube voltage to 50 kV (effective energy of 27.9 keV), 80 kV (32.2 keV), and 120 kV (38.7 keV). Dose linearity was evaluated by changing the number of irradiation to 1, 5, and 40 times, which corresponded to 0.53, 5.32, and 21.4 mGy. Batch uniformity was evaluated by calculating the coefficient of variation ofHp(3) obtained from 10 Vision badges. Angular dependence was evaluated at 0° (perpendicular to the incident direction of x-rays), 30°, 60°, 75°, and 90°. The Vision badge and optically stimulated luminescence (OSL) dosimeter were attached to the inside of the radioprotective glasses, worn on the endoscopist phantom, and theHp(3) obtained from both dosimeters were compared. TheHp(3) obtained from the Vision badge with 38.7 keV was 3.8% higher than that with 27.9 keV. The Vision badge showed excellent linearity (R2= 1.00) with the air kerma up to 21.4 mGy. The coefficient of variation of theHp(3) for 10 Vision badges was 3.47%. The relative dose of the Vision badge decreased as the angle increased up to 75°, but increased at 90°. TheHp(3) obtained by the OSL dosimeter and the Vision badge were decreased as the endoscopist phantom was turned away from the patient phantom. TheHp(3) that was obtained by the Vision badge was 35.5%-55.0% less than that obtained by the nanoDot. In conclusion, the Vision badge showed specific angular dependence due to its shape, but satisfactory basic properties were exhibited for all characteristics. In phantom study, the Vision badge showed generally similar trends with the OSL dosimeter.

Half-value layer measurements using solid-state detectors and single-rotation technique with lead apertures in spiral computed tomography with and without a tin filter

Solid-state detectors (SSDs) may be used along with a lead collimator for half-value layer (HVL) measurement using computed tomography (CT) with or without a tin filter. We aimed to compare HVL measurements obtained using three SSDs (AGMS-DM+ , X2 R/F sensor, and Black Piranha) with those obtained using the single-rotation technique with lead apertures (SRTLA). HVL measurements were performed using spiral CT at tube voltages of 70-140 kV without a tin filter and 100-140 kV (Sn 100-140 kV) with a tin filter in increments of 10 kV. For SRTLA, a 0.6-cc ionization chamber was suspended at the isocenter to measure the free-in-air kerma rate (K ˙ air ) values. Five apertures were made on the gantry cover using lead sheets, and four aluminum plates were placed on these apertures. HVLs in SRTLA were obtained fromK ˙ air decline curves. Subsequently, SSDs inserted into the lead collimator were placed on the gantry cover and used to measure HVLs. Maximum HVL differences of AGMS-DM+ , X2 R/F sensor, and Black Piranha with respect to SRTLA without/with a tin filter were - 0.09/0.6 (only two Sn 100-110 kV) mm, - 0.50/ - 0.6 mm, and - 0.17/(no data available) mm, respectively. These values were within the specification limit. SSDs inserted into the lead collimator could be used to measure HVL using spiral CT without a tin filter. HVLs could be measured with a tin filter using only the X2 R/F sensor, and further improvement of its calibration accuracy with respect to other SSDs is warranted.

Cultural adaptation, content, and protocol of a feasibility study of school-based "Let's learn about emotions" intervention for Finnish primary school children

Introduction

Emotional awareness and emotion regulation are crucial for cognitive and socio-emotional development in children. School-based interventions on socio-emotional skills have the potential to prevent these problems and promote well-being of children. The Japanese school-based program, Universal Unified Prevention Program for Diverse Disorders (Up2-D2), has shown preventive effects on mental health of children in Japan. The aims of this protocol paper are to describe the unique process of adapting the Up2-D2 from Eastern to Western context, and to present a feasibility study of the intervention, conducted in Finland.

Methods

The cultural adaptation process started with the linguistic translation of materials, followed by the modification of language to fit the Finnish context. While the Japanese ideology was saved, some content was adapted to fit Finnish school children. Further modifications were made based on feedback from pupils and teachers. The Finnish version of the program was named "Let's learn about emotions" and consisted of 12 sessions and targeted 8- to 12-year-old pupils. A teacher education plan was established to assist Finnish teachers with the intervention, including a workshop, teachers' manual, brief introductory videos, and online support sessions. A feasibility study involving 512 4th graders in the City of Hyvinkää, South of Finland, was conducted. It assessed emotional and behavioral problems, classroom climate, bullying, loneliness, perception of school environment, knowledge of emotional awareness, and program acceptability.

Discussion

The originality of this study underlies in the East-West adaptation of a cognitive behavioral therapy-based program. If promising feasibility findings are replicated in Finland, it could pave the way for further research on implementing such programs in diverse contexts and cultures, promoting coping skills, awareness, social skills and early prevention of child mental health problems.

Ethics

The ethical board of the University of Turku gave ethics approval for this research. The educational board of the City of Hyvinkää accepted this study.

Number of computed tomography scanners and regional disparities based on population and medical resources in Japan

This study aimed to discover the associations between the number of computed tomography (CT) scanners and the population, as well as number of medical resources to identify regional disparities in Japan. The number of CT scanners was tabulated for each detector row of CT scanners for hospitals and clinics in each prefecture. The number of CT scanners, patients, medical doctors, radiological technologists, facilities, and beds per 100,000 population was compared. Additionally, the number of hospitals with ≥ 200 beds and multidetector-row CT scanners with ≥ 64 rows were tabulated, and their ratios were calculated. Medical institutions in Japan have installed 14,595 scanners. CT scanners per 100,000 population were the highest in Kochi Prefecture, although the number of CT scanners in hospitals was the highest in Tokyo Prefecture. Multivariate analysis revealed the number of radiological technologists (β coefficient: 0.49; P = 0.03), facilities (β coefficient: 0.12; P < 0.01) and beds (β coefficient: 0.46; P < 0.01) as independent factors for the number of CT scanners. Prefectures with a high proportion of hospitals with ≥ 200 beds also had a relatively high proportion of CT scanners with ≥ 64 rows (P < 0.01). Our survey revealed an association between regional disparities in the number of CT scanners in Japan, the population, and number of medical resources. A positive correlation was found between hospital size and number of CT scanners with ≥ 64 rows.

Energy-based Hp(3) measurement using solid-state detector

This study aimed to develop an energy-based Hp(3) measurement method using a solid-state detector (SSD). Incident and entrance surface air kerma were measured using an ionization chamber placed free-in-air and in front of an anthropomorphic or slab phantom. Subsequently, three SSDs were placed free-in-air, and half-value layer and readings were obtained. After measurements, an X-ray beam quality correction factor $\left ({{k}}_{{Q},{{Q}}_{\mathbf{0}}}^{{SSD}}\right)$, backscatter factor (BSF) and conversion factor from incident air kerma to Hp(3) (C3) were determined. Then, the incident air kerma by SSD $\left ({{K}}_{{a},{i}}^{{SSD}}\right )$, Hp(3) and Hp(3)/${{K}}_{{a},{i}}^{{SSD}}$ were calculated. The ${{k}}_{{Q},{{Q}}_{\mathbf{0}}}^{{SSD}}$ was almost consistent for all SSDs. The C3 and BSF were found to increase as tube potential increased. The Hp(3)/${{K}}_{{a},{i}}^{{SSD}}$ calculated with the anthropomorphic and slab phantoms were consistent within 2.1% and 2.6% for all SSDs, respectively. This method improves the energy dependence of Hp(3) measurement and can estimate the Hp(3) measurement error for dedicated Hp(3) dosemeters.

Radiation dose and factors related to exceeding the diagnostic reference level in 496 transnasal ileus tube placement procedures from the REX-GI study

OBJECTIVE

We aimed to examine the factors contributing to radiation exposure exceeding the DRL of the transnasal ileus tube placement in this post hoc analysis from the cohort of the REX-GI study.

METHODS

Patients with transnasal ileus tubes were enrolled in the rex-gi study from may 2019 to december 2020. We investigated the endoscope insertion time (min), procedure time (min), tube insertion length (cm), fluoroscopy time (FT: min), air kerma at the patient entrance reference point (K_a.r: mGy), and air kerma-area product (P_KA: Gycm²). The third quartile value of the P_KA value was calculated as the diagnostic reference level (DRL) value. We explored the factors associated with radiation exposure exceeding the DRL.

RESULTS

In the REX-GI study, 496 patients who underwent transnasal ileus tube placement were enrolled. The median age of the patients was 71 years. The median endoscopy insertion time, procedure time, and tube insertion length were 6 min, 20 min, and 170 cm, respectively. The third quartile/median FT, K_a.r, and P_KA were 18/11.9 min, 99.2/54.4 mGy, and 46.9/28 Gycm², respectively. The third quartile value of P_KA (47 Gycm²) was set as the DRL value. There were differences in distribution by the hospital. Compared with procedures under the DRL, the FT (19 vs 10 min), procedure time (25 vs 18 min), and tube insertion length (185 vs 165 cm) were significantly longer for procedures above the DRL.

CONCLUSION

We report the DRL for transnasal ileus tube placement in Japan. A longer procedure time and tube insertion length may be associated with DRL exceedance.

ADVANCES IN KNOWLEDGE

Transnasal ileus tube placement under fluoroscopy guidance is a standard clinical procedure for bowel obstruction. However, the appropriate radiation dose level has not yet been established.We report the (DRL) for transnasal ileus tube placement in Japan. A longer procedure time and tube insertion length may be associated with DRL exceedance.

Eye lens dose for medical staff assisting patients during computed tomography: comparison of several types of radioprotective glasses

Medical staff sometimes assists patients in the examination room during computed tomography (CT) scans for several purposes. This study aimed to investigate the dose reduction effects of four radioprotective glasses with different lead equivalents and lens shapes. A medical staff phantom was positioned assuming body movement restraint of the patient during chest CT, and H_p(3) at the eye surfaces of the medical staff phantom and inside the lens of the four types of radioprotective glasses were measured by changing the distance of the staff phantom from the gantry, eye height, and width of the nose pad. The H_p(3) at the right eye surface with glasses of 0.50-0.75 mmPb and 0.07 mmPb was approximately 83.5% and 58.0%, respectively, lower than that without radioprotective glasses. The dose reduction rates at left eye surface increased with over-glass type glasses by 14%-28% by increasing the distance from the CT gantry to the staff phantom from 25 to 65 cm. The dose reduction rates at the left eye surface decreased with over-glass type glasses by 26%-31% by increasing the height of the eye lens for the medical staff phantom from 130 to 170 cm. The H_p(3) on the left eye surface decreased by 46.9% with the widest nose pad width compared to the narrowest nose pad width for the glasses with adjustable nose pad width. The radioprotective glasses for staff assisting patients during CT examinations should have a high lead equivalent and no gap around the nose and under the front lens.

Physical and visual evaluations of CT image quality of large low-contrast objects with visual model-based iterative reconstruction technique: a phantom study

We aimed to verify whether the image quality of large low-contrast objects can be improved using visual model-based iterative reconstruction (VMR) while maintaining the visibility of conventional filtered back projection (FBP) and reducing radiation dose through physical and visual evaluation. A 64-row multi-slice CT system with SCENARIA View (FUJIFILM healthcare Corp. Tokyo, Japan) was used. The noise power spectrum (NPS), task-based transfer function (TTF), and signal-to-noise ratio (SNR) were physically evaluated. A low contrast object as a substitute for a liver mass was visually evaluated. In the noise measurement, STD1 showed an 18% lower noise compared to FBP. STR4 was able to reduce noise by 58% compared to FBP. The NPS of VMR was similar to those of FBP from low to high spatial frequency. The NPS of VMR reconstructions showed a similar variation with frequency as FBP reconstructions. STD1 showed the highest 10% TTF, and higher 10% TTF was observed with lower VMR level. The SNR of VMR was close to that of FBP, and higher SNR was observed with higher VMR level. In the results of the visual evaluation, there was no significant difference in visual evaluation between STD1 and FBP (p = 0.99) and between STD2 and FBP (p = 0.56). We found that the NPS of VMR images was similar to that of FBP images, and it can reduce noise and radiation dose by 25% and 50%, respectively, without decreasing the visual image quality compared to FBP.

Accuracy of patient dose estimation in cone beam computed tomography in breast irradiation by size-specific dose estimates with position correction

This study aims to investigate the effects of the position correction of size-specific dose estimates (SSDE) on patient dose estimation in cone beam computed tomography (CBCT). The relationship between the phantom position and absorbed dose in the right breast was studied using optically stimulated luminescence dosimeters and a simulated human body phantom. The effect of position correction for CT dose index (CTDI) on SSDE was investigated in 51 patients who underwent right breast irradiation by comparing the SSDE with position correction and SSDE without position correction. The absorbed dose in the right breast tended to decrease by 10.2% as the phantom was placed away from the center of CBCT. The mean and standard deviation of SSDE were 2.54 ± 0.29 and 2.92 ± 0.30 mGy with and without position correction, respectively. The SSDE with position correction was 13.1% lower than that without position correction (p < 0.05). SSDE was different when the patient's torso center was located at the isocenter of CBCT, and when it was not. The same tendency was seen in the case of the breast. Therefore, if the center of the patient is not at the acquisition center of the CT scanner, position correction is required when estimating SSDE.

[Accuracy Evaluation of Air Kerma-area Product of Over-couch-type X-ray Fluoroscopic System]

PURPOSE

The purpose of this study was to evaluate the accuracy of incident air kerma (K_a,r) and air kerma-area product (P_KA) displayed on over-couch-type X-ray fluoroscopic systems by comparing them with the measured values.

METHODS

An ionizing chamber was placed at the patient entrance reference point to measure the K_a,r. The P_KA was calculated by multiplying the K_a,r by the irradiation area. These measured values were compared with the displayed values.

RESULTS

The differences between measured and displayed K_a,r and P_KA were less than ±35%, which was the criteria of the Japanese Industrial Standards (JIS). However, the accuracy of the displayed values differed depending on the manufacturer and the device.

CONCLUSION

Although no error exceeding the JIS criteria was observed, it is necessary to understand the characteristics of the X-ray fluoroscopic systems related to displayed dose and to manage the systems by performing dose measurements periodically.

[Organ and Effective Doses Using Automation Organ Dose Estimation Software for Lung Cancer Screening Using Low-dose Computed Tomography]

PURPOSE

The purpose of this study was to evaluate the differences in the organ doses and the effective doses using three types of automated organ dose estimation software for low-dose computed tomography (CT) screening for lung cancer and to evaluate the correlations between each dose and size-specific dose estimates (SSDEs).

METHODS

Seventy-two adults who underwent low-dose CT screening for lung cancer were included, and the organ doses and the effective doses were calculated using each of automated organ dose estimation software. We evaluated differences between software for the organ doses and the effective doses and the correlations between each dose and SSDEs.

RESULTS

Differences in organ doses and effective doses were observed among the software. The organ doses showed a strong correlation (r=0.833-0.995) with SSDEs for organs within the scan range. The effective doses showed a strong correlation (r=0.830-0.970) with SSDEs, although there were significant differences among the software.

CONCLUSION

Although the organ doses and the effective doses differed between software, it may be possible to estimate them from SSDEs by using linear regression equations.

Reducing stray radiation with a novel detachable lead arm support in percutaneous coronary intervention

Background

Placing radioprotective devices near patients reduces stray radiation during percutaneous coronary intervention (PCI), a promising technique for treating coronary artery disease. Therefore, lead arm support may effectively reduce occupational radiation dose to cardiologists.

Purpose

We aimed to estimate the reduction of stray radiation using a novel detachable lead arm support (DLAS) in PCI.

Materials and methods

A dedicated cardiovascular angiography system was equipped with the conventional 0.5‐mm lead curtain suspended from the table side rail. The DLAS was developed using an L‐shaped acrylic board and detachable water‐resistant covers encasing the 0.5‐, 0.75‐, or 1.0‐mm lead. The DLAS was placed adjacent to a female anthropomorphic phantom lying on the examination tabletop at the patient entrance reference point. An ionization chamber survey meter was placed 100 cm away from the isocenter to emulate the cardiologist's position. Dose reduction using the L‐shaped acrylic board, DLAS, lead curtain, and their combination each was measured at five heights (80–160 cm in 20‐cm increments) when acquiring cardiac images of the patient phantom with 10 gantry angulations, typical for PCI.

Results

Median dose reductions of stray radiation using the L‐shaped acrylic board were 9.0%, 8.8%, 12.4%, 12.3%, and 6.4% at 80‐, 100‐, 120‐, 140‐, and 160‐cm heights, respectively. Dose reduction using DLAS with a 0.5‐mm lead was almost identical to that using DLAS with 0.75‐ and 1.0‐mm leads; mean dose reductions using these three DLASs increased to 16.2%, 45.1%, 66.0%, 64.2%, and 43.0%, respectively. Similarly, dose reductions using the conventional lead curtain were 95.9%, 95.5%, 83.7%, 26.0%, and 19.6%, respectively. The combination of DLAS with 0.5‐mm lead and lead curtain could increase dose reductions to 96.0%, 95.8%, 93.8%, 71.1%, and 47.1%, respectively.

Conclusions

DLAS reduces stray radiation at 120‐, 140‐, and 160‐cm heights, where the conventional lead curtain provides insufficient protection.

Automated development of the contrast-detail curve based on statistical low-contrast detectability in CT images

Purpose

We have developed a software to automatically find the contrast–detail (C–D) curve based on the statistical low‐contrast detectability (LCD) in images of computed tomography (CT) phantoms at multiple cell sizes and to generate minimum detectable contrast (MDC) characteristics.

Methods

A simple graphical user interface was developed to set the initial parameters needed to create multiple grid region of interest of various cell sizes with a 2‐pixel increment. For each cell in the grid, the average CT number was calculated to obtain the standard deviation (SD). Detectability was then calculated by multiplying the SD of the mean CT numbers by 3.29. This process was automatically repeated as many times as the cell size was set at initialization. Based on the obtained LCD, the C–D curve was obtained and the target size at an MDC of 0.6% (i.e., 6‐HU difference) was determined. We subsequently investigated the consistency of the target sizes for a 0.6% MDC at four locations within the homogeneous image. We applied the software to images with six noise levels, images of two modules of the American College of Radiology CT phantom, images of four different phantoms, and images of four different CT scanners. We compared the target sizes at a 0.6% MDC based on the statistical LCD and the results from a human observer.

Results

The developed system was able to measure C–D curves from different phantoms and scanners. We found that the C–D curves follow a power‐law fit. We found that higher noise levels resulted in a higher MDC for a target of the same size. The low‐contrast module image had a slightly higher MDC than the distance module image. The minimum size of an object detected by visual observation was slightly larger than the size using statistical LCD.

Conclusions

The statistical LCD measurement method can generate a C–D curve automatically, quickly, and objectively.

Usefulness of a lead-acrylic shield for reducing lens dose of assistant in x-ray CT examination

In computed tomography (CT) examinations, the usefulness of protective glasses for reducing lens exposure to assistants has been reported. The present study aimed to compare the dose reduction effect for assistants with lead-acrylic shields and protective glasses (0.07 mm Pb, 0.5 mm Pb) during CT examination. The air dose distribution in a CT examination room with and without a lead-acrylic shield was compared. It was found that the amount of scattered radiation was significantly reduced by installing a lead-acrylic shield at the CT gantry aperture. Moreover, the reduction rate of air kerma at the assistant's lens was higher using the lead acrylic shield than with the protective glasses-95.7% during head holding and 76.1% during assisted ventilation.

[Scientific Research Group Report: Nationwide Survey on Radiation Exposure of Pediatric CT Examination in Japan (2018)]

PURPOSE

To understand the latest pediatric computed tomography (CT) exposure required for the revision of national DRLs.

METHODS

A questionnaire was sent to 409 facilities where the members of the Japanese Society of Radiological Technology and the Japanese Society of Pediatric Radiology are enrolled. We investigated the imaging conditions, CTDI_vol, and DLP of the pediatric head, chest, and abdominal CT examinations.

RESULTS

In all, 43 facilities (11%) responded to our survey. multi detector-row CT (MDCT) systems were available in all surveyed facilities. More than 98% of the MDCT systems had more than 64 detector rows. The CTDI_vol of all CT protocols was lower than the NDRL due to the progress of updating to MDCTs with radiation exposure reduction functions such as an iterative reconstruction, but the DLP of head and abdominal CT protocols of some age group were higher than NDRL.

CONCLUSION

It is necessary to review the imaging protocol with the attending physician and radiologist and consider further optimization of medical exposure.

The measurement of entrance surface dose using optically stimulated luminescence dosimeters for determining average glandular dose in digital breast tomosynthesis: Measurement and simulation study

This study aimed to evaluate the feasibility of using optically stimulated luminescence dosimeters (OSLDs), nanoDots, for the determination of an average glandular dose (AGD) with a specific digital breast tomosynthesis (DBT) system, whereas the X-ray tube was fixed (2D mode) and moved (3D mode). The entrance surface air kerma (ESAK) was measured by placing the nanoDots on the surface of a polymethyl methacrylate (PMMA) phantom with 25, 28, and 34 kV W/Rh techniques. The experimental setup of the ESAK measurement was simulated using a Monte Carlo simulation code to determine the ESAK and the backscatter factor (BSF). The AGD was calculated by dividing the ESAK values over the corresponding BSF factors for each PMMA phantom thickness and multiplying the AGD conversion factors. The AGD determination by the nanoDots variated within ±5% for both 2D and 3D modes, compared to those determined using an ionization chamber. The results were similarly observed for the simulation, except for the 25 kV on the 3D mode. Regarding the International Atomic Energy Agency technical reports series number 457, the nanoDots can be used for the AGD determination with realistic 2D and 3D image acquisitions based on ±10% uncertainty.

[Effect of Automatic Extraction Accuracy by Different Image Reconstruction Methods Using a Three-dimensional Image Analysis System for Pulmonary Segmentectomy Preoperative CT Angiography]

This study aimed to determine the optimal image reconstruction method for preoperative computed tomography (CT) angiography for pulmonary segmentectomy. This study enrolled 20 patients who underwent contrast-enhanced CT examination for pulmonary segmentectomy. The optimal image reconstruction algorithm among four different reconstruction algorithms (filtered back projection, hybrid iterative reconstruction, model- based iterative reconstruction, and deep learning reconstruction [DLR]) was investigated by assessing the CT numbers, vessel extraction ratios, and misclassification ratios. The vessel extraction ratios for main and subsegment branches reconstructed using DLR were significantly higher than those using other reconstruction algorithms (96.7% and 90.8% for pulmonary artery and vein, respectively). The misclassification ratios at the right upper lobe pulmonary vessels (V1 and V2) were especially high because they were close to the superior vena cava, and their CT numbers were similar in all four reconstructions. In conclusion, the DLR allows a high extraction rate of pulmonary blood vessels and a low misclassification rate of automatic extraction.

Determination of geometric information and radiation field overlaps on the skin in percutaneous coronary interventions with computer-aided design-based X-ray beam modeling

PURPOSE

This study aimed to develop a method for the determination of the source-to-surface distance (SSD), the X-ray beam area in a plane perpendicular to the beam axis at the entrance skin surface (A_p ), and the X-ray beam area on the actual skin surface (A_s ) during percutaneous coronary intervention (PCI).

MATERIALS AND METHODS

Male and female anthropomorphic phantoms were scanned on a computed tomography scanner, and the data were transferred to a commercially available computer-aided design (CAD) software. A cardiovascular angiography system with a 200 × 200 mm flat-panel detector with a field-of-view of 175 × 175 mm was modeled with the CAD software. Both phantoms were independently placed on 40 mm thick pads, and the examination tabletop at the patient entrance reference point. Upon panning, the heart center was aligned to the central beam axis. The SSD, A_p , and A_s were determined with the measurement tool and Boolean intersection operations at 10 gantry angulations.

RESULTS

The means and standard deviations of the SSD, A_p , and A_s for the male and female phantoms were 573 ± 15 and 580 ± 15 mm, 8799 ± 1009 and 9661 ± 1152 mm² , 10495 ± 602 and 11913 ± 600 mm² , respectively. The number of A_s overlaps for the male and female phantoms were 15/45 and 21/45 view combinations, respectively.

CONCLUSIONS

CAD-based X-ray beam modeling is useful for the determination of the SSD, A_p , and A_s . Furthermore, the knowledge of the A_s distribution helps to reduce the A_s overlap in PCI.

[A Simple Measurement Method for Verifying the Accuracy of the Displayed Dose on an Over-couch-type X-ray Fluoroscopic System]

The purpose of this study was to establish a simple measurement method to verify the accuracy of incident air kerma (K_{a, r}) and air kerma area product (P_KA) displayed on an over-couch-type X-ray fluoroscopy system. A dosimeter was located at the patient entrance reference point, and the irradiation field size was set to 10×10 cm. A lead plate was placed on the couchtop to protect the image receptor, and the duration of fluoroscopy was set to 1 min. The K_{a, r} was measured with the proposed method and the Japanese Industrial Standards (JIS) method on three X-ray fluoroscopy units of different manufactures. The effect of backscattered X-rays from the lead plate was calculated using Monte Carlo methods. The errors of the displayed K_{a, r} and P_KA to the measured K_{a, r} and P_KA with our proposed method were calculated. There was no significant difference in the measured K_{a, r} between the proposed method and the JIS method in all units. The effect of backscattered X-ray was ≤0.5%. The errors of displayed K_{a, r} and P_KA to those measured were in the range of 3.4 to 15.7% and -4.1 to 20.3%, respectively, which met the tolerance for accuracy of ±35% in accordance with the JIS method. We found that our proposed method was simple and that the accuracy of measured values was comparable to that of the JIS method.

Effect of equalization filters on measurements with kerma-area product meter in a cardiovascular angiography system

Purpose

This study aimed to evaluate the effect of equalization filters (EFs) on the kerma‐area product (KAPQKM) and incident air‐kerma (Ka,i,QKM) using a kerma‐area product (KAP) meter. In addition, potential underestimations of the Ka,i,QKM values by EFs were identified.

Materials and methods

A portable flat‐panel detector (FPD) was placed to measure the X‐ray beam area (A) and EFs dimension at patient entrance reference point (PERP). Afterward, a 6‐cm³ external ionization chamber was placed to measure incident air‐kerma (Ka,i,Qext) at PERP instead of the portable FPD. KAP reading and Ka,i,Qext were simultaneously measured at several X‐ray beam qualities with and without EFs. The X‐ray beam quality correction factor by KAP meter (kQ,Q0KM) was calculated by A, Ka,i,Qext and KAP reading to acquire the KAPQKM and Ka,i,QKM. Upon completion of the measurements, KAPQKM, Ka,i,QKM, and Ka,i,Qext were plotted as functions of tube potential, spectral filter, and EFs dimension. Moreover, Ka,i,QKM/Ka,i,Qext values were calculated to evaluate the Ka,i,QKM underestimation.

Results

The kQ,Q0KM values increased with an increase in the X‐ray tube potential and spectral filter, and the maximum kQ,Q0KM was 1.18. KAPQKM and Ka,i,QKM decreased as functions of EFs dimension, whereas Ka,i,Qext was almost constant. Ka,i,QKM/Ka,i,Qext decreased with an increase in EFs dimension but increased with an increase in tube potential and spectral filter, and the range was 0.55–1.01.

Conclusions

Ka,i,QKM value was up to approximately two times lower than the Ka,i,Qext values by EFs. When using the Ka,i,QKM value, the potential Ka,i,QKM underestimation with EFs should be considered.

A comparison of automatic and manual compensation methods for the calculation of tube currents during off-centered patient positioning with a noise-based automatic exposure control system in computed tomography

Automatic exposure control (AEC) is used to optimize the X-ray tube output during computed tomography (CT) scans. However, calculation of the tube current by AEC can be affected when a patient is not aligned with the rotational center of the X-ray tube. An automatic couch height-positioning compensation mechanism provides a corrective function when the patient is off-center. In this study, we aimed to (a) evaluate the performance characteristics of the positioning compensation mechanism and (b) confirm whether our proposed compensation method can be properly applied to a noise-based AEC system even if the CT device is not equipped with a positioning compensation mechanism. An elliptical phantom was scanned at various table heights on systems without/with the positioning compensation mechanism. Expressions describing the offset from the gantry's isocenter and adjusted standard deviation settings were derived and used in our proposed compensation method. A phantom was scanned at various table heights with our proposed compensation method, and volume CT dose index (CTDI_vol) and image noise levels were obtained. An anthropomorphic chest phantom was also scanned using the proposed compensation method to verify its accuracy. When the positioning compensation mechanism was used, it yielded a constant CTDI_vol and image noise levels at various table heights tested. A comparison between our proposed method and the positioning compensation mechanism for both the elliptical and chest phantoms yielded similar CTDI_vol. Therefore, both automatic and manual positioning compensation methods are useful for avoiding AEC miscalculations in off-centered patient positioning cases.

Evaluation of the relationship between phantom position and computed tomography dose index in cone beam computed tomography when assuming breast irradiation

This study aims to investigate the influence of the phantom position on weighted computed tomography dose index (CTDIw ) in cone beam computed tomography (CBCT) when assuming breast irradiation. Computed tomography dose index (CTDI) was measured by the x-ray volume imaging of CBCT using parameters for image-guided radiation therapy (IGRT) in right breast irradiation. The measurement points of CTDI ranged from 0 (center) to 16 cm in the right-left (RL) direction, and from 0 (center) to 7.5 cm in the anterior-posterior (AP) direction, which assumed right breast irradiation. A nonuniform change exists in the relative value of CTDIw when the phantom deviated from the isocenter of CBCT. The CTDIw was ~30% lower compared with the value at the isocenter of CBCT when the phantom deviated 7.5 and 16 cm at the AP and RL directions, respectively. This study confirmed the influence of the phantom position on the CTDI values of CBCT. The CTDI measured at the isocenter of CBCT overestimates that measured at the irradiation center of the breast.

Effects of Rice Wine Lees on Cognitive Function in Community-Dwelling Physically Active Older Adults: A Pilot Randomized Controlled Trial

BACKGROUND

Rice wine lees (RWL), a Japanese traditional fermented product, is a rich source of one-carbon metabolism-related nutrients, which may have beneficial effects on cognitive function.

OBJECTIVES

We aimed to examine the effect of the RWL on cognitive function in community-dwelling physically active older adults.

DESIGN

Double-blind, randomized, placebo-controlled study (clinical trial number: UMIN 000027158).

SETTING

Community-based intervention including assessments conducted at the University of Hyogo and a public liberal arts school in Himeji City, Japan.

PARTICIPANTS

A total of 35 community-dwelling older adults (68-80 years) who performed mild exercise before and during the trial were assigned to either the RWL (n=17) or the placebo group (n=18).

INTERVENTION

Daily consumption of 50 g RWL powder, which contained one-carbon metabolism-related nutrients, or the placebo powder (made from soy protein and dextrin) for 12 weeks. Both supplements included equivalent amounts of energy and protein.

MEASUREMENTS

Montreal Cognitive Assessment, computerized cognitive function test, and measurements of serum predictive biomarkers (transthyretin, apolipoprotein A1, and complement C3) were conducted at baseline and follow-up.

RESULTS

Visual selective attention and serum transthyretin significantly improved in the RWL group, whereas there was no significant change in the placebo group. No significant group difference was observed in the remaining cognitive performance tests.

CONCLUSIONS

RWL supplements seem to have a few effects on cognitive function in community-dwelling physically active older adults. However, the impact was limited; therefore, further studies with sufficient sample size are warranted to elucidate this issue.

[An Evaluation of Radiation Dose for Wide Volume Scan during Chest CT]

PURPOSE

A volume scan can cover a range of 160 mm with a single gantry rotation. It can be performed sequentially (a wide volume [WV] scan) to cover more than 160 mm, and volume Xact+ (Xact+) can be used when volume scan is done to extend the reconstruction area. The purpose of this study was to investigate the dose distribution and organ doses for a WV scan during chest CT.

METHOD

We arranged radiophotoluminescence glass dosimeters (RPLDs) linearly on the surface and inside of the phantom to evaluate the dose distribution along the z-axis. We also placed RPLDs at the lens, thyroid, and breast positions to evaluate organ doses. We performed WV and helical scans and WV scan using Xact+.

RESULT

The absorbed doses increased at the borders of the volume scans, and dose peaks were observed there. The organ doses for the WV scan outside the acquisition range were lower than those for the helical scan. The organ doses inside the acquisition range changed by the locations of borders.

CONCLUSION

The WV scan increases the absorbed doses at the overlapping scanned regions, which can be reduced by using Xact+.

Characterization of Small Dosimeters Used for Measurement of Eye Lens Dose for Medical Staff during Fluoroscopic Examination

This study aimed to evaluate the property of small dosimeters used for measuring eye lens doses for medical staff during fluoroscopic examination. Dose linearity, energy dependence, and directional dependence of scattered X-rays were evaluated for small radiophotoluminescence glass dosimeters (RPLDs), those with a tin filter (Sn-RPLDs), and small optically stimulated luminescence dosimeters (OSLDs). These dosimeters were pasted on radioprotective glasses, and accumulated air kerma was obtained after irradiating the X-rays to a patient phantom. Strong correlations existed between fluoroscopic time and accumulated air kerma in all types of dosimeters. The energy dependence of Sn-RPLD and OSLD was smaller than that of RPLD. The relative dose value of the OSLD gradually decreased as the angle of the OSLD against the scattered X-rays was larger or lower than the right angle in the horizontal direction. The ranges of relative dose values of RPLD and Sn-RPLD were larger than that of OSLD in the vertical direction. The OSLDs showed lower doses than the RPLDs and Sn-RPLDs, especially on the right side of the radioprotective glasses. These results showed that RPLDs, Sn-RPLDs, and OSLDs had different dosimeter properties, and influence measured eye lens doses for the physician, especially on the opposite side of the patient.

Evaluation of peak skin dose during percutaneous coronary intervention procedures: relationship with fluoroscopic pulse rate and target vessel

This study aimed to evaluate the relationship between the peak skin dose (PSD) associated with radiation skin injury and the fluoroscopic pulse rate or target vessel during percutaneous coronary intervention (PCI) procedures. We consecutively included 213 patients who underwent PCI procedures. The fluoroscopic time (FT), total number of cine frames, reference air kerma (RAK), and PSD were compared between the two types of fluoroscopic pulse rates (10 and 7.5 pulses/s) and among target vessels. The total number of X-ray tube angulations for each target vessel was also investigated. The median FT was 21.5 min in the 10 pulses/s group and 19.4 min in the 7.5 pulses/s group (p = 0.068, Wilcoxon rank sum test). The median PSD in the 10 pulses/s group was 749 mGy, which was significantly higher than that in the 7.5 pulses/s group (549 mGy) (p < 0.001). The median RAK in the right coronary artery (RCA) was equivalent to that in the left anterior descending artery. However, among the target vessels, the median PSD tended to be the highest in the RCA. There was a difference in the X-ray tube angulation used depending on the target vessel. PCI in the RCA used the left anterior oblique angle more frequently than PCI in the other vessels and tended to use only one angulation. The calculated PSD was related to the target vessel of the PCI procedure, and it was also closely related to the X-ray tube angulation.

CT dose management of adult patients with unknown body weight using an effective diameter

PURPOSE

To assess the usefulness of effective diameter (D_eff) for CT dose management of adult patients with unknown body weight.

METHODS

A total of 642 adult patients whose height and weight had been measured before CT examination (chest CT using Aquilion Prime SP, 428 patients; chest CT using Biograph mCT, 100 patients; and abdominal CT using Aquilion Prime SP, 114 patients) were retrospectively examined between April 2018 and September 2019. The D_eff was automatically calculated from the lateral diameter on a CT localizer radiograph by a dose management software (Radimetrics). In order to determine the correlation between body weight and D_eff, we compared volume CT dose index and dose length product between patients with body weight between 50 and 70 kg and those with D_eff equivalent to body weight between 50 and 70 kg. Correlation analysis was performed by Pearson's product-moment correlation, and statistical analyses were performed by using t-test.

RESULTS

The correlation coefficient values between body weight and D_eff were 0.920 for chest CT using Aquilion Prime SP, 0.929 for chest CT using Biograph mCT, and 0.805 for abdominal CT using Aquilion Prime SP. In both chest and abdominal CT scans, there were no significant differences in volume CT dose index and dose length product between patients with body weight between 50 and 70 kg and those with D_eff equivalent to body weight between 50 and 70 kg.

CONCLUSIONS

The D_eff may be useful as a somatometric parameter for CT dose management of adult patients with unknown body weight.