Radiological Physics and Technology最新文献

Previous studies have shown that high kilovoltage (kV) angiographic imaging techniques can reduce radiation doses to patients more effectively than using low kV techniques. While radiologists often accept the resulting image quality, a detailed quantitative comparison between these techniques remains limited. This study aimed to evaluate and compare the quality of cerebral angiographic images acquired using high kV (79-90 kV) and low kV (68-82 kV) techniques on a biplane digital subtraction angiography (DSA) system. Images were analyzed from patients with cerebral aneurysms as well as a quality assurance phantom (TO DSA), focusing on 2-dimensional angiography (2D-DSA). The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured at various vascular locations in posteroanterior (PA) axial and lateral views. While demographic data did not differ between groups, CNR for PA axial view and PA phantom images produced with high kV was significantly lower than that with low kV. In contrast, the high kV technique demonstrated higher SNR values in both PA and lateral views compared to the low kV technique. Radiation dose per frame confirmed a reduction in dose for the high kV protocol. Conversely, TO DSA images acquired using high kV had a lower SNR than those from low kV. The low kV technique achieved better vessel contrast, as evidenced by its higher CNR compared to the high kV technique. However, it also resulted in a lower SNR in patient images and a higher radiation dose. Protocol selection should, therefore, aim to optimize the trade-off between image quality and radiation exposure.

Purpose: The purpose of this study was to validate the accuracy of a method for determining the iodine contrast dose using effective diameter (D_eff) when performing dynamic computed tomography (CT) scans of the upper abdomen in patients with unknown body weight (BW).

Methods: D_eff was measured at the heart, at the right diaphragm upper edge, and at the right pulmonary rib diaphragm levels in the localizer radiograph and axial images. Correlation coefficients between D_eff and BW were determined for each cross section.

Results: D_{eff_axial} and BW showed the highest correlation at the right diaphragm upper edge level in men (r_S = 0.862) and at the right pulmonary rib diaphragm level in women (r_S = 0.890).

Conclusions: The BW estimated from D_eff showed a strong correlation with measured BW and may serve as a practical alternative in cases where BW is unknown.

This study evaluated dose differences to the heart, left anterior descending coronary artery (LADCA), and left main coronary artery (LMCA) between diastolic and systolic heart phases in radiation therapy for left-sided breast cancer using deep inspiration breath-hold (DIBH). Diastolic and systolic doses to the heart, LADCA, and LMCA were analyzed using electrocardiogram-gated cardiac computed tomography images from 15 women. Radiation therapy plans were created for a total dose of 50 Gy in 25 fractions. Parameters assessed included volume, D_mean, D_2%, V_5Gy, V_10Gy, V_20Gy, and V_25Gy for the heart; D_mean, D_2%, V_5Gy, V_10Gy, and V_20Gy for the LADCA; and D_mean and D_2% for the LMCA. The D_mean of the heart was 5.10 ± 3.04 Gy and 5.03 ± 3.05 Gy for diastole and systole, respectively (mean ± 1 standard deviation), and D_2% was 37.44 ± 16.03 Gy and 36.15 ± 16.76 Gy. Statistically significant differences were found in the D_mean. LADCA doses showed no significant differences, possibly due to anatomical variations. The D_mean of the LMCA was 1.88 ± 0.23 Gy and 2.02 ± 0.28 Gy for diastole and systole, and D_2% was 2.05 ± 0.28 Gy and 2.21 ± 0.30 Gy, with both parameters being statistically significantly higher during systole. Although small, cardiac-phase-dependent dose variations under DIBH were statistically significant, confirming that current non-ECG-gated DIBH remains adequate for cardiac dose management.

Accurate estimation of absorbed doses in organs/tissues is essential for effective internal dosimetry. This is especially the case for positron-emission tomography-utilized radiopharmaceuticals that contain positron-emitting radionuclides. To achieve this, it is essential to calculate S-coefficients (S), basic coefficients representing the absorbed dose in the target organ per unit of nuclear transformation in the source organ. In addition, as the evolution of computational phantoms from stylized, voxelized, to mesh-type models continues, updating the S-coefficients to correspond with the new phantom generation becomes required. We employed the DoseCalcs Monte Carlo platform to estimate S-coefficients for four positron-emitting radionuclides, namely, C-11, N-13, O-15, and F-18. Based on decay and energy data for emitted positrons that were obtained from ICRP Publication 107, the simulations involved 24 regions as internal radiation sources in the male and female mesh-type phantoms of the International Commission on Radiological Protection (ICRP). We calculated the S-coefficients for 25 radiosensitive target regions. The graphs of S-coefficients for all target $\leftarrow$ source pairs exhibit similar trends for the four radionuclides. We compared the results with the OpenDose database, which calculated S-coefficients for voxelized phantoms. The comparison showed that the S-coefficients and the OpenDose voxelized values were very close for most target regions in the mesh-type phantoms. However, discrepancies were observed in specific cases, such as thyroid $\leftarrow$ UBCs and liver $\leftarrow$ HeW. These discrepancies arise primarily from the differences in organs/tissues locations and shapes, as well as the differences in material composition, which is distributed across the large inter-distance between the source and target, contributing to significant variations.

High-resolution cone-beam computed tomography (HR-CBCT) during cerebral angiography raises concerns regarding high radiation exposure in exchange for high spatial resolution, but detailed dose assessments are lacking. This study aimed to accurately estimate organ dose (OD) and effective dose (ED) for HR-CBCT using the NCIRF Monte Carlo software, which incorporates projection-specific variations in X-ray output, and to derive dose conversion coefficients for clinical application. Four sites prone to cerebral aneurysms were scanned using a phantom, and exposure parameters were recorded for each projection angle. OD and ED were calculated using NCIRF. Simulation accuracy was validated by comparing lens doses measured with radiophotoluminescence glass dosimeters, and the results were compared with a conventional method that ignores projection-specific dose variations. The maximum brain OD was 46.2 mGy for males and 61.7 mGy for females. ED ranged from 0.70 to 0.89 mSv for males and 0.86-1.11 mSv for females. The relative difference between simulated and measured lens doses was less than 6.0%, demonstrating good agreement. The proposed method reduced lens dose error by approximately 20% compared to the conventional method. Conversion coefficients were calculated for each site and sex to estimate OD and ED from the air kerma-area product. This study demonstrated that dynamic Monte Carlo simulation incorporating projection-specific exposure variations can provide highly accurate dose estimations for HR-CBCT. The derived conversion coefficients offer a practical tool that can support optimization of patient radiation protection in clinical settings using similar equipment and protocols.

This study aimed to predict optimal imaging conditions for dynamic chest radiography (DCR) using exposure times derived from auto exposure control (AEC) during chest X-ray (CXR) imaging and to validate their effectiveness against conventional body mass index (BMI)-based protocols. A total of 579 datasets from patients who underwent both CXR and DCR on the same day were analyzed. The relationship between exposure time for CXR and tube current-time product (mAs) in DCR was assessed, and linear regression models were developed for perfusion and ventilation imaging. Using these models, a refined protocol was developed and evaluated based on deviation from the target S-value (3000). The S-value represents the system sensitivity index in general X-ray imaging, and the target value of 3000 was used as a reference. The evaluation was performed using absolute error (AE) from which mean absolute error (MAE) and mean absolute percentage error (MAPE) were calculated. A strong correlation was observed between exposure time for CXR and mAs values of DCR (r = 0.901 for perfusion; r = 0.831 for ventilation). The refined protocol showed significantly lower MAE and MAPE than the conventional protocol, with narrower error distributions and fewer outliers, indicating improved consistency in image quality. The proposed protocol, based on exposure time for CXR, enables stable imaging conditions in DCR regardless of patient body size or condition and is expected to support dose optimization and standardization of image quality.

We evaluated atlas selection methods for multi-atlas-based segmentation (MABS) in breast cancer radiotherapy planning. Forty-five patients were divided into 30 atlas and 15 test cases. The 30 atlases were stratified into three groups based on breast separation, height, and volume. Firstly, MABS was performed on each of the 30 atlas cases using the remaining 29 atlases. Secondly, MABS was performed on 15 test cases using the 30 atlases. The Dice similarity coefficient (DSC) was calculated to assess the agreement between MABS and manual segmentation. The DSC was found to increase as more atlases were selected. Although this led to an increase in the computational time, the implementation of patient stratification reduced the computational time compared with using the entire dataset. Atlas selection from the height-matched and volume-matched tertile datasets provided median DSC values > 0.9. Breast height may be a practical surrogate for breast volume which is unknown before segmentation.