Radiological Physics and Technology最新文献

In plain chest radiography (CXR), automatic exposure control (AEC) is generally used to standardize image quality. In contrast, dynamic chest radiography (DCR) systems preliminarily require manual setting of tube current-time products (mAs value). Body mass index (BMI) of patients is one of the indexes to determine the mAs value; however, standardization is limited because the anatomical differences are not considered. In this study, for further standardization, we propose a practical procedure to determine the individual mAs value of DCR using data obtained from CXR. To evaluate its effectiveness, we retrospectively analyzed 97 patients who underwent both CXR and DCR on the same day. DCR was performed in the following procedures: (1) obtain the relationship between the mAs value and the exposure indicator (S value, Konica Minolta, Inc.) obtained in CXR acquisition, (2) calculate the mAs value of DCR for the target S value of 2500, and (3) record the S value in DCR. The tube voltages for CXR and DCR were set to 120 kV and 100 kV with a copper filter, respectively. The differences in exposure doses were corrected by measuring the air kerma using a CdTe detector. As a result, the S values of CXR and DCR were 133 ± 13 (Coefficient of Variation (CV) = 9.9%) and 2629 ± 207 (CV = 7.9%), respectively, which were not dependent on the patient size based on evaluating the S values of five classified BMI groups. In conclusion, our proposed procedure enables standardization of the image quality in DCR by optimizing the patient-specific exposure conditions.

In ²⁰¹Tl myocardial perfusion single-photon emission computed tomography (SPECT), gastric wall uptake can impact the inferior wall. This study aimed to evaluate the effectiveness and usefulness of the masking on un-smoothed image (MUS) method for ²⁰¹Tl myocardial perfusion SPECT. A hemispherical gastric wall phantom was created to simulate the gastric fundus located closest to the myocardium, and the activity was enclosed to achieve an SPECT count ratio against the myocardium equivalent to that observed in clinical practice. The minimum values of the defect chip in the circumferential profile curve were compared for six SPECT count ratios and seven gap distances. In the conventional method, increasing SPECT count ratios or gap distances interfered with myocardial perfusion SPECT evaluation. Artifacts were less apparent when the MUS method was applied. The MUS method effectively suppressed the gastric wall uptake on ²⁰¹Tl myocardial perfusion SPECT.

We aimed to develop a technique to precisely measure the shrinkage of immobilization sheets (ISs) using a three-dimensional (3D) tracking of multiple points on IS using a near-infrared camera. A thermoplastic sheet and an elastomer sheet were used in this study. The inter-marker distance (IMD) of neighboring marker pairs and the triangular area (TA) formed by neighboring three markers were analyzed as a function of time since molding each IS. Thermal distance ratio (TDR), IMD normalized to IMD after 48 h, and thermal area ratio (TAR), TA normalized to TA after 48 h, were analyzed using an exponential function. The 3D visualization of the initial shrinkage amplitude (ISA) was created for each IS. The mean ISA and the time constant (TC) in the exponential function (ISA, TC) for horizontal and vertical pairs were (0.34 $\pm$ 0.06, 3.9 $\pm$ 0.9) and (0.60 $\pm$ 0.05, 7.6 $\pm$ 0.9) for HFT and (0.13 $\pm$ 0.02, 25.0 $\pm$ 4.7) and (0.06 $\pm$ 0.03, 4.7 $\pm$ 3.5) for SF, respectively. The mean (ISA, TC) for HFT and SF were (0.76 $\pm$ 0.07, 7.1 $\pm$ 0.9) and (0.22 $\pm$ 0.03, 17.7 $\pm$ 4.2), respectively. Horizontal pairs showed smaller ISA and shorter TC than vertical pairs for HFT, while horizontal pairs showed larger ISA and longer TC than vertical pairs for SF, possibly due to different chemical characteristics of each material under the effect of mechanical force. The mean TDR and TAR are considered useful for evaluating the gross property of IS. The visualized distributions of ISA are considered useful to provide spatial information for investigating relationships between actual handlings and shrinkage of IS.

Image quality, in addition to radiation dose, is the most important physical parameter in digital mammography. Image quality should be periodically monitored using the CDMAM phantom. The aim of this study is to investigate the effect of the number of analyzed images on the result of threshold image contrast measurements using the CDMAM phantom in different versions. The images obtained using two versions of the CDMAM phantom, i.e., 3.4 and 4.0, were analyzed. The image analysis was performed and repeated 10 times for 2, 4, 6, 8, 12, 16, 24, and 32 images from a pool of 43 images, separately for each phantom. For the CDMAM 3.4 phantom, a statistical difference was demonstrated between the following groups: S2 vs S6 (p < 0.006), S6 vs S16 (p < 0.001), S6 vs S24 (p < 0.002), S6 vs S32 (p < 0.021), S8 vs S16 (p < 0.019), S8 vs S24 (p < 0.048). For the CDMAM 4.0 phantom, a statistically significant difference was demonstrated between all groups and the N2 group (p < 0.000). For the CDMAM 3.4 phantom, the most favorable number of images required for analysis cannot be clearly determined. For the CDMAM 4.0 phantom, it is recommended to perform 24 images for analysis. Particular attention should be paid when determining the threshold image contrast for a disk diameter of 0.1 mm, as this parameter is used during exposure automation control.

In therapy with Synchrony® mounted on Radixact®, the fiducial marker (FM) and adrenal gland metastasis, which shift with respiratory phase, require margin compensation for high-dose prescriptions. Although compensation is critical, no studies have examined the margin to compensate for the respiratory phase shift. Therefore, we aimed to suggest the compensating margin for the FM and adrenal metastasis shift along with respiratory phase. We used images from four-dimensional computed tomography (4DCT) taken twice and gated CT taken once before therapy initiation with available contour data for FM and adrenal gland metastasis in each image. The distance between the FM and the center of the gross tumor volume (GTV) in each image of a ten-set 4DCT was defined as the correlating association, and a relative cumulative frequency distribution was created based on it. The values of the margins compensating for respiratory displacement were obtained from the relative cumulative frequency distribution in the right-left/posterior-anterior/superior-inferior (S-I) directions. In cases wherein the FM was placed inside the GTV, the margin values decreased in the S-I direction.

To quantify radiation dose reduction in radiotherapy treatment-planning CT (RTCT) using a deep learning-based reconstruction (DLR; AiCE) algorithm compared with adaptive iterative dose reduction (IR; AIDR). To evaluate its potential to inform RTCT-specific diagnostic reference levels (DRLs). In this single-institution retrospective study, 4-part RTCT scans (head, head and neck, lung, and pelvis) were acquired on a large-bore CT. Scans reconstructed with IR (n = 820) and DLR (n = 854) were compared. The 75th-percentile CTDI_vol and DLP (CTDI_IR, DLP_IR vs. CTDI_DLR, DLP_DLR) were determined per site. Dose reduction rates were calculated as (CTDI_DLR - CTDI_IR)/CTDI_IR × 100% and similarly for DLP. Statistical significance was assessed by the Mann-Whitney U-test. DLR yielded CTDI_vol reductions of 30.4-75.4% and DLP reductions of 23.1-73.5% across sites (p < 0.001), with the greatest reductions in head and neck RTCT (CTDI_vol: 75.4%; DLP: 73.5%). Variability also narrowed. Compared with published national DRLs, DLR achieved 34.8 mGy and 18.8 mGy lower CTDI_vol for head and neck versus UK-DRLs and Japanese multi-institutional data, respectively. DLR substantially lowers RTCT dose indices, providing quantitative data to guide RTCT-specific DRLs and optimize clinical workflows.

Rotational cerebral angiography requires accurate dosimetry. The National Cancer Institute Dosimetry System for Radiography and Fluoroscopy (NCIRF), a Monte Carlo-based dosimetry software, can evaluate the organ dose (OD) and effective dose (ED) with higher accuracy than the conventional Monte Carlo software (PCXMC). We estimated the OD and ED for three-dimensional digital subtraction angiography (3D-DSA) and cone beam computed tomography (CBCT) using the NCIRF, reflecting dose variations during rotational cerebral angiography. The 3D-DSA and CBCT simulation parameters were obtained by rotational imaging of a physical head phantom using the Artis Q biplane system. The air kerma area product for each projection was determined based on the ratio of the tube current-time product for each projection; the NCIRF was used with male and female voxel-type reference computational phantoms. To validate the simulation results, the lens dose of the phantom was measured using radiophotoluminescence glass dosimeters and compared to the simulated lens dose. The highest ODs were delivered to the brain: 8.8 mGy (males) and 11.6 mGy (females) in 3D-DSA and 50.0 mGy (males) and 59.4 mGy (females) in CBCT. The EDs were 0.27 mSv (males) and 0.35 mSv (females) in 3D-DSA and 1.49 mSv (males) and 1.83 mSv (females) in CBCT. Lens doses differed within 8.0% between measurements and simulations, with 45.9-65.5% overestimation in simulations that did not account for dose variability. Simulations that considered dose variability using the NCIRF more accurately estimated OD and ED in rotational cerebral angiography.

Accurate lateral knee radiographs are essential for assessing pathology and planning surgery. However, achieving adequate femoral condyle overlap is technically challenging because of individual variations in lower limb alignment. We analyzed the alignment-dependent bone morphology and proposed practical X-ray tube angles to optimize lateral imaging. Full-length lower limb radiographs of 212 normal and 191 knees with osteoarthritis (KOA) were examined. The lateral distal femoral angle (LDFA) and medial proximal tibial angle were measured to classify the alignment into varus, neutral, and valgus types. The LDFA increased with varus alignment in both the normal (89.1°, 88.0°, and 85.2°) and KOA knees (90.2°, 88.0°, and 85.0°). The joint line orientation consistently exhibited an apex-distal pattern. The distal femoral tangent angle (θ = 90° - LDFA) ranged from - 0.2° to 5.0°, providing reference targets for X-ray tube inclination. This alignment-based approach improved imaging reproducibility and diagnostic accuracy in both normal and KOA knees.

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.