A highly sensitive dosimeter with a small scintillation probe was devised for precise dosimetry of CT exposure. The probe, which was constructed using a small plastic scintillator and optical fibers coupled with photo-multipliers, had the advantages of directional and dose-rate independence of sensitivity on incident x-rays. Sensitivity, however, increased with x-ray effective energy, having a rate of 10% / 10keV at 50keV. The scintillation probe was placed on the surface and in the center of a human chest phantom with elliptical cross-section that was constructed using tissue-equivalent materials, and dose profiles were measured over a 300 mm scan width using a Toshiba TCT300 conventional scanner. Multiple scan average doses(MSADs)were estimated from the dose profiles as a function of the number of scans, and it was found that they were not saturated for the maximum number of 30 scans with a 10 mm slice and 10 mm distance between scans. Absorbed doses on the phantom's surface differed according to the position of the surface, where doses on the top were about 1.7 times larger than those on the side. MSADs estimated for the 30 scans on the top and side surfaces and in the center were 33.0, 19.6, and 34.1mGy, respectively, with maximum MSAD at the center of the phantom.
Observer performance experiments were performed with a digital radiography system (Regius model 330:DR system)using photostimulable storage phosphors(RbBr:TI^+)and a conventional screen-film system (HGM-UR1:S-F system)for chest radiography. A phantom lung with simulated opacities was used (nodule, miliary opacity, consolidation, and reticular opacity), and was exposed with the DR system (sampling distance:175μm, 2, 048×2, 048 pixels, 12bits)and S-F system under the same conditions of exposure. Eight physicians with 10 years of almost daily practice in interpreting chest radiographs evaluated the visibility of the simulated opacities and ranked them. The ranking data were analyzed by means of normalized ranked data and the scoring method. Statistical analyses were performed by two-way analysis of variance (ANOVA) and the least significant difference (LSD) method with Studentized t-value, and the confidence coefficients of the ranking were calculated. Evaluation of the visibility of simulated opacities in the lung field showed that the chest radiographs obtained with the DR system using THX2 (look-up table:LUT for chest radiography) were equal to or better than those obtained with the S-F system. In conclusion, the DR system (THX2 with LUT) is a highly useful modality for chest radiography because of its superior performance in comparison with the S-F system under the radiographic conditions used in this study.
Physical factors (physically evaluated values)and psychological factors (fuzzy measurements)of breast x-ray images were comprehensively evaluated by applying breast x-ray images to an extended stratum-type fuzzy integrating model. In addition, x-ray images were evaluated collectively by integrating the quality (sharpness, graininess, and contrast)of x-ray images and three representative shadows (fibrosis, calcification, tumor)in the breast x-ray images. We selected the most appropriate system for radiography of the breast from three kinds of intensifying screens and film systems for evaluation by this method and investigated the relationship between the breast x-ray images and noise equivalent quantum number, which is called the overall physical evaluation method, and between the breast x-ray images and psychological evaluation by a visual system with a stratum-type fuzzy integrating model. We obtained a linear relationship between the breast x-ray image and noise-equivalent quantum number, and linearity between the breast x-ray image and psychological evaluation by the visual system. Therefore, the determination of fuzzy measurement, which is a scale for fuzzy evaluation of psychological factors of the observer, and physically evaluated values with a stratum-type fuzzy integrating model enabled us to make a comprehensive evaluation of x-ray images that included both psychological and physical aspects.
Cinefilm will gradually be replaced by some digital media for the archiving of angiographic images. We constructed a network system of coronary angiographic movies with an image server, two acquisition systems(Catheter Laboratory), and eight image viewers. We examined the image transmission speed of each modality, and that of the latest one was 7.2 frames per second. The review speed from network iamge to viewer is less than half the acquisition rate, but the review speed is not reduced by multiple, simultaneous requests to the server for the same data
MRCA by two-dimentional-segmented k-space turbo FLASH(2D-STFL)is a noninvasive method of describing the coronary artery. However, this technique is not widely used owing to the complexity of handling. We examined 262 branches of the coronary artery in 160 cases to determine whether MRCA could be used as a method of evaluating stenosis of the coronary artery. MRCA images were classified into five groups(normal, vessel narrowing, reduced intensity, breakage of vessel, and inability to image), and we then compared the MRCA findings with percent diameter stenosis demonstrated by coronary angiography. The sensitivity specificity, and accuracy of MRCA for coronary arterial stenosis of 90% or more, breakage of vessel, and inability to image were 0.70, 0.87, and 0.85, respectively. Further, the sensitivity, specificity, and accuracy of MRCA for coronary arterial stenosis of 75% or more, including reduced intensity, were 0.83, 0.79, and 0.80, respectively, and those of 50% or more were 0.95, 0.86, and 0.90, respectively, including reduced intensity. In conclusion, MRCA is considered to be highly useful as a noninvasive method for the evaluation of coronary lesions.