Radiological Physics and Technology最新文献

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.

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.

To assess the reproducibility of native T1 value measurements across different myocardial slice positions and cardiac phases using a 1.5T magnetic resonance (MR) system. Twenty-seven healthy male volunteers (mean age 31.2 ± 4.8 years) underwent native T1 mapping on a 1.5T MR scanner (Ingenia, Philips) using a modified look-locker inversion recovery (MOLLI) 5-(3)-3 sequence. Short-axis images were acquired at the basal, mid, and apical levels of the left ventricle during both diastolic and systolic phases. Each acquisition was repeated twice. Native T1 values were measured using semi-automated region of interest (ROI) placement with Cvi42 software. Reproducibility was evaluated using Bland-Altman analysis. Native T1 values were 982.1 ± 27.9 ms (base), 988.3 ± 21.3 ms (mid), and 993.8 ± 49.2 ms (apex) during diastole, and 981.1 ± 35.1 ms (base), 989.1 ± 24.3 ms (mid), and 984.4 ± 33.3 ms (apex) during systole. No significant differences were observed between diastolic and systolic phases or across slice positions. Bland-Altman analysis revealed the narrowest 95% limits of agreement for mid-ventricular slices in systole (- 24.8 to 22.7 ms) and the widest for apical slices in diastole (- 48.1 to 56.2 ms). Reproducibility was consistently superior during systole compared to diastole. Native myocardial T1 values at 1.5T demonstrated reproducibility across both cardiac phases and slice positions in healthy subjects. However, systolic imaging provided narrower limits of agreement, particularly at the apex. Therefore, imaging in systole is recommended for assessing apical T1 values.

The global increase in computed tomography (CT) use, highlighted by a 40% growth in South Korea over the past decade, has made CT a significant source of medical radiation exposure, emphasizing the need for accurate effective dose (ED) estimation. This study aimed to develop population-specific effective dose conversion factors (k-factors) for brain CT examinations across the range of tube voltages used in Korean hospitals. Clinical dose parameters were obtained from the Korean National CT Dose Index Registry (KNCTDIR), which compiles large-scale dose-length product (DLP) data from 45 hospitals nationwide. The mean, maximum, and minimum kVp and DLP values were selected to represent typical clinical variations. Monte Carlo simulations were performed using GATE version 10.0b8 with Korean-sized XCAT phantoms for adult and pediatric groups. Organ and effective doses were calculated following ICRP 103 tissue-weighting factors, and k-factors were derived for each age, sex, and voltage condition. The results showed consistent k-factors across the evaluated voltage range, with only minimal sex-related differences. Infants had the highest coefficients (0.0029 mSv/mGy·cm), while pediatric k-factors were lower and remained relatively stable from ages 2 to 15 years. Comparisons with previous Korean and international studies revealed notable quantitative differences, emphasizing the need for updated, population-specific coefficients. The revised k-factors facilitate practical and consistent effective-dose estimation in Korean brain CT procedures.