Objectives: The aim of this study was to evaluate the effectiveness of scatter correction in the portable chest radiography. Methods: Digital radiographies were performed without anti-scatter grid (grid), with the scatter correction and with the grid ratio of 3 : 1 in this study. The scatter fraction and the detectability of low contrast signals were measured using the four acrylic phantoms of different thicknesses. The chest phantom radiographs were assessed subjectively, in random order, by six radiologic technologists. Results: The scatter fraction was higher in the no-grid technique, and was lower for the grid technique. The detectability of low contrast signals did not significantly differ between the scatter correction and the grid technique (p>0.05). The area under the receiver operating characteristic curve for the grid technique was higher than that for the scatter correction technique (0.888 vs. 0.855), although no significant difference was found between the grid and the scatter correction technique (p> 0.05). The ability to detect the nasogastric tube was significantly better in the grid technique (p<0.001). Discussion: In the scatter correction technique, the ability of scatter removal increased as the scatter fraction increased. The scatter correction technique was unnecessary to extremely accurate alignment. In addition, patient dose can be reduced by the scatter correction technique. Conclusions: It seemed to be effective for the scatter correction in the portable chest radiography.
Purpose: The aim of this study was to evaluate the effects of inaccurate attenuation correction due to the misalignment between the computed tomography (CT)-based μ-map and the positron emission tomography (PET) data on a brain PET. Methods: CT and PET scans were performed on a 3-dimension (3D) brain phantom, in which the grey matter region was filled with 18F-fluorodeoxyglucose (18F-FDG), and the skull region was filled with/without the bone-equivalent solution. The shifted PET images relative to the CT image were generated by the software-based translation of PET data in the cephalad/caudal and right directions, with a magnitude of the shift up to 30 mm and a step size of 5 mm. The regions of interest (ROIs) were drawn on the areas of the temporal lobes, parietal lobes, thalami, and cerebellums in the no-shifted image (reference). For each ROI, the radioactivity concentrations in the shifted images were compared with those of the reference. Results: The errors in the radioactivity concentrations were increased with the increasing magnitude of the shift in all brain regions except for thalamus. For a 5 mm shift in the right direction, ± 10% errors were observed in the left/right temporal lobes. The accuracy of the radioactivity concentration in the temporal lobe was very sensitive to misalignment in the right directions. Conclusion: The misalignment between CT-based μ-map and PET data had larger effects on the surface regions of the brain rather than on deep brain structures.
Palpation is a standard clinical tool to diagnose abnormal stiffness changes in soft tissues. However, it is difficult to palpate the supraspinatus muscle because it locates under the trapezius muscle. The magnetic resonance elastography (MRE) uses harmonic mechanical excitation to quantitatively measure the stiffness (shear modulus) of both the superficial and deep tissues. The purpose of this study was to build a vibration system for applying the MRE to the supraspinatus muscle. In this study, a power amplifier and a pneumatic pressure generator were used to supply vibrations to a vibration pad. Six healthy volunteers underwent MRE. We investigated the effects of position (the head of the humerus and the trapezius muscle) of the vibration pad on the patterns of wave propagation (wave image). When the vibration pad was placed in the trapezius muscle, the wave images represented clear wave propagation. On the other hand, when the vibration pad was placed in the head of the humerus, the wave images represented unclear wave propagation. This result might be caused by wave interferences resulting from the vibrations from bones and an intramuscular tendon of the supraspinatus muscle. The mean shear modulus also was 8.12 ± 1.83 (mean ± SD) kPa, when the vibration pad was placed in the trapezius muscle. Our results demonstrated that the vibration pad should be placed in the trapezius muscle in the MRE of the supraspinatus muscle.
Purpose: The contrast agent used in the diagnostic department has high atomic numbers and might influence dose deposition in the particle therapy. In particular, the influence of gadolinium-based (Gd) contrast agent on range in carbon ion radiotherapy has not yet been evaluated. For this reason, we avoid carbon treatment and planning computed tomography (CT) acquisition on days when the contrast-enhanced magnetic resonance image (MRI) is performed. In this study, we evaluated the time required for this beam range effect to vanish by evaluating the temporal changes in the CT values after an enhanced MRI as well as the stopping power of Gd solution. Materials and methods: Two types of diluted solutions with Gd contrast agent were used for comparing their transferred stopping power (TSP) and measured stopping power (MSP). The TSP was calculated with a CT value to stopping power ratio table that was created previously. Additionally, to evaluate in vivo attenuation, we measured the CT values in the renal pelvis from the CT images with and without contrast agent for 73 patients. Results: The maximum difference between the TSP and MSP was 85%. The difference between the TSP after 4 hours and the TSP with non-enhanced cases was less than 1%. Moreover, the difference between the MSP after 1 hour and the MSP with non-enhanced cases was less than 0.1%. Conclusion: It was found that the impact of Gd contrast agent can be neglected 1 hour after administration for carbon beam irradiation and 4 hours after for planning the CT image acquisition.
Purpose: The purpose of this study was to investigate the effects of the metal artifact reduction using single energy metal artifact reduction (SEMAR) with a prosthetic hip joint in different field of view (FOV). Methods: A prosthetic hip joint was arranged at the center of the phantom. The phantom images were scanned by changing calibrated-FOV (C-FOV) of 240, 320, 400, and 500 mm. Those images were reconstructed by changing the display-FOV (D-FOV) of 120, 180, 240, and 320 mm. The metal artifact reduction with the SEMAR was evaluated by calculating the artifact index (AI) and its decrease ratio. Results: The AI of C-FOV (500 mm) and D-FOV (120, 180, 240, or 320 mm) were 15.8, 15.8, 15.7, and 14.4 with SEMAR. For changed C-FOV, the AI of C-FOV (240 mm) was significantly higher than any other C-FOVs. The AI of C-FOV (240 mm) was 29.8–30.0 and that of the other C-FOV were 12.4–15.8 with SEMAR. In addition, the decrease ratio of AI was 52.2–54.1% for C-FOV (240 mm) and 58.9–73.2% for the other C-FOVs. Conclusion: Although the SEMAR decreased the metal artifact, the effect of reducing the metal artifact was affected by C-FOV.
Purpose: The purpose of this study was to evaluate the advantage of 80-row non-helical scan methods (NH) for the head computed tomography (CT). Methods: We calculated the noise power spectrum (NPS), contrast-to-noise ratio (CNR), CT values and standard deviation (SD) at slice position, and coefficient of variation (CV) value in head phantom. This study compared the NH method with the helical scan method (HE). Results: The NPS and CNR of NH were improved compared to the HE in equivalent volume-CT dose index (CTDIvol). However, the NH was inferior to the HE in CT values and the SD at slice position. The CV values of NH were increased than the HE in the skull base. On the other hand, the CV values of NH were decreased than the HE in basal ganglia and parietal. Conclusions: The non-helical scan method in head CT have advantage for the detection of lesion in basal ganglia and parietal.