[Usefulness of Post-processing Scatter Correction in Portable Abdominal Radiography Using a Low Ratio Anti-scatter Grid].

OBJECTIVES: The aim of this study was to evaluate an influence of post-processing scatter correction in portable abdominal radiography using a low ratio anti-scatter grid (grid). METHODS: To assess tube voltage on portable abdominal radiography, a burger phantom was used to measure for inverse of image quality figure (IQFinv). For evaluation of the influence on using or not the grid, IQFinv were measured. Abdominal phantom radiographies were assessed subjectively, in random order, by six radiologic technologists. The radiographies were performed without scatter correction [IG (-)] and with scatter correction at equivalent for grid ratio 6 [IG (6)] and 8 [IG (8)]. RESULTS: There was no significant decrease in IQFinv with 75 and 80 kV in comparison of 70 kV. Even processing scatter correction, IQFinv with using the grid was significantly higher than that without using the grid. The ability to detect nasogastric tube and stomach gas were significantly better in the scatter correction. Deviation index for IG (6) and IG (8) were significantly lower than that of IG (-). DISCUSSION: Portable abdominal radiographies will be improved image quality by utilizing scatter correction, although, it is necessary to consider the scatter correction processing as this may significant decrease deviation index in the practical situation. CONCLUSION: The post-processing scatter correction should be useful for detection nasogastric tube and stomach gas in portable abdominal radiography.

Examination for Effectiveness of Scatter Correction in Portable Chest Radiography.

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.

[Usefulness of spatially adaptive noise reduction processing in computer-assisted diagnosis system for bone scintigraphy].

OBJECTIVES: The goal of this study was to assess the diagnostic accuracy of Pixon-processed images in comparison with raw images for computer-assisted interpretation of bone scintigraphy (BONENAVI). METHODS: Whole-body scans of 57 patients with prostate cancer who had undergone bone scintigraphy for suspected bone metastases were obtained approximately 3 h after intravenous injection of 740 MBq (99m)Tc-methylene diphosphonate. We obtained two image sets: raw images and images processed using the Pixon method. Artificial neural network (ANN) values, bone scan index (BSI), number of hotspots and regional ANN value of two images set were automatically calculated by the BONENAVI software. Areas under the receiver operator characteristic curves (AUC) were calculated in patient-based and lesion-based analyses. RESULTS: In ten cases with bone metastases, ANN, BSI and number of hotspots for processed images were equivalent to those in the raw images. However, in 47 cases without bone metastases, ANN, BSI and number of hotspots for processed images showed significantly lower values than those for the raw images (p<0.05). Sensitivity, specificity and accuracy of the raw images were 90.2, 44.7 and 65.9%, and those of the processed images were 90.2, 57.4 and 72.7%, respectively. The AUC for processed images was equivalent to that for raw images. CONCLUSIONS: Specificity and accuracy in the detection of bone metastases showed the Pixon-processed images to have high diagnostic performance. We conclude that the precision of computer-assisted interpretation of bone scintigraphy can be enhanced by using Pixon processing.

Artifacts caused by insufficient contrast medium filling during C-arm cone-beam CT scans: a phantom study.

We investigated artifacts due to late-arriving contrast medium (CM) during C-arm cone-beam computed tomography. We scanned a phantom filled with water or with 100, 50, or 5% v/v concentrations of CM and then virtually produced CM-delayed projection data by partially replacing the projection images. Artifacts as a function of concentration, percentage of filling time, and size and position of the filling area were assessed. In addition, we used an automatic power injector with different injection delays to inject CM during the scans. A decrease in filling times caused by a lag in CM arrival during the scan resulted in a decrease in pixel values, distortion of the filling area, and appearance of streak artifacts. Even a delay of approximately 20% in CM arrival in the total scan time resulted in obvious distortion of the filling area. The distortion and streak artifacts tended to worsen at higher CM concentrations. Use of a minimum CM concentration based on the purpose of the examination and constant filling at the target region are effective for avoiding these artifacts.

Iterative estimation of coherent-scattering profiles from given positions by use of a single-direction beam.

The coherent-scattering distribution is useful for characterization of materials in the medical field, and obtaining this information from a given position in the object is a useful new diagnostic approach. We propose a simpler geometric approach, which requires only a single-direction X-ray beam with no collimator in front of the detector. This method iteratively estimates coherent-scattering profiles from given positions along the beam path, based on the projections positioned at different object-to-detector distances. We confirmed the proposed calculation algorithm by numerical simulation and performed a simple experiment including attenuation correction. The accuracy of matching with the original profiles was dependent on the number of iterations, the distance between the first and second detectors, the distance between two objects, and the shape of the scattering profile. Whereas multiple scattering was the main problem in the experiment, the calculated scattering profiles matched well with the original profile. This technique indicates the feasibility of developing a coherent-scatter imaging system.