We measured modulation transfer functions (MTFs) of liquid crystal displays (LCDs) by rectangular waveform analysis. This method is taking a picture of the bar pattern on the monitor surface with a digital camera, and analyzing the picture with a personal computer. The monitors used are the monochrome LCDs of 1M(about 1 million of the number of pixels), 2M, 3M, and 5M, and the color LCDs of 1M, 2M, 3M. The display of 2M used IPS system and VA system. 3M and 5M of the monochrome LCDs were examined when there was a protective filter or not. Two or three displays are used for each system. In both the monochrome and the color LCDs, MTFs became high as the matrix size increased. In the monochrome LCDs, MTF in horizontal direction was higher than MTF in vertical direction. And there was no difference when a protective filter was used or not. MTFs of the color LCDs had little difference in horizontal direction and the vertical direction. MTFs of the LCDs are influenced on the form and the fill factor of a pixel, and composition of sub-pixels.
An automatic extraction of pulmonary emphysema area on 3-D chest CT images was performed using an adaptive thresholding technique. We proposed a method to estimate the ratio of the emphysema area to the whole lung volume. We employed 32 cases (15 normal and 17 abnormal) which had been already diagnosed by radiologists prior to the study. The ratio in all the normal cases was less than 0.02, and in abnormal cases, it ranged from 0.01 to 0.26. The effectiveness of our approach was confirmed through the results of the present study.
We previously developed a scheme to automatically detect pulmonary nodules on CT images, as a part of computer-aided diagnosis (CAD) system. The proposed method consisted of two template-matching approaches based on simple models that simulate real nodules. One was a new template-matching technique based on a genetic algorithm (GA) template matching (GATM) for detecting nodules within the lung area. The other one was a conventional template matching along the lung wall [lung wall template matching (LWTM)] for detecting nodules on the lung wall. After the two template matchings, thirteen feature values were calculated and used for eliminating false positives. Twenty clinical cases involving a total of 557 sectional images were applied; 71 nodules out of 98 were correctly detected with the number of false positives at approximately 30.8/case by applying two template matchings (GATM and LWTM) and elimination process of false positives. In this study, five features were newly added, and threshold-values of our previous features were reconsidered for further eliminating false positives. As the result, the number of false positives was decreased to 5.5/case without elimination of true positives.
We have applied the equivalence statistical test designs in the success rate to the equivalence test in the ROC analysis. Here, in the ROC analysis, it is difficult to determine the acceptable difference. We consider the ROC curve in the binormal model, and the maximum allowable value of the true difference in the area under the binormal ROC curve between two treatments is considered to be the one corresponding to the maximum acceptable value of the true difference in the sensitivity with the same specificity (or specificity with same sensitivity) between two treatments. Here, we have shown the tolerable true difference of the areas under the binormal ROC curve will be calculated in the case of the same slope in the binormal ROC plane, if an acceptable true difference of the sensitivity with same specificity (or specificity with same sensitivity) is given. So, one is able to test the equivalence in diagnostic performance of two medical image tests by using the ROC analysis, by testing a null hypothesis of an acceptable difference calculated from an acceptable sensitivity (or specificity) difference versus an alternative hypothesis of a true difference less than it.
The purpose is to verify the clinical usefulness of newly developed visual test-objects including chest images and contrast test images for a safe usage of CRT monitor. Various kinds of test images including the contrast-detail method were created. Here, the 11 CRT monitor display conditions that simulated the CRT monitors degraded by the long-term usage were tested. The soft-copy test-images under 11 kinds of monitor-luminance conditions were observed. From the results of the threshold contrast values at which the target was just visible, we determined the border zone of CRT monitor luminance below which the diagnostic performance was inferior to that of the normal CRT monitors. In the darker display conditions in which the maximum luminance was 0.607 or less of the normal CRT luminance (480 cd/m2), the correct detection rates of targets were significantly inferior to that in the normal CRT display condition (480 cd/m2)(p<0.05). In the perception study of the contrast test images luminance where the monitor became apparently too dark for the image interpretation was 0.52 to 0.59 of the normal CRT luminance. The method with proposed visual test-objects is practical for daily check of diagnostic CRT monitors and convenient for diagnostic radiologists.
An advanced auto-stereoscopic display is described that permits the observation of a stereo pair by several persons simultaneously without the use of special glasses and any kind of head tracking devices for the viewers. The system is composed of a right eye system, a left eye system and a sophisticated head tracking system. In the each eye system, a transparent type color liquid crystal imaging plate is used with a special back light unit. The back light unit consists of a monochrome 2D display and a large format convex lens. The unit distributes the light of the viewers' correct each eye only. The right eye perspective system is combined with a left eye perspective system is combined with a left eye perspective system by a half mirror in order to function as a time-parallel stereoscopic system. The viewer's IR image is taken through and focused by the large format convex lens and feed back to the back light as a modulated binary half face image. The auto-stereoscopic display employs the TTL method as the accurate head tracking. The system was worked as a stereoscopic TV phone between Duke University Department Tele-medicine and Nagoya University School of Medicine Department Radiology using a high-speed digital line of GIBN. The applications are also described in this paper.
We are developing automated-detection schemes for the masses and clustered microcalcifications on laser-digitized mammograms (0.1 mm, 10-bit resolution, 2000 X 2510) by using a conventional workstation. The purpose of this paper is to provide an overview of our recent schemes and to evaluate the current performance of the schemes. The fully automated computer system consists of several parts such as the extraction of breast region, detection of masses, detection of clustered microcalcifications, classification of the candidates, and the display of the detected results. Our schemes tested with more than 200 cases of Japanese women achieved an about 95% (86%) true-positive rate with 0.61 (0.55) false-positive masses (clusters) per image. It was found that the automated method has the potential to aid physicians in screening mammograms for breast tumors. Initial results for the mammograms digitized with the pixel sizes of 25, 50, and 100 micrometers are also discussed, in which a genetic algorithm (GA) technique was applied to the detection filter for the microcalcifications. It was indicated from the experiment with a breast phantom that 100- micrometers pixel size is not enough for the computer detection of microcalcifications, and it seems that at least 50-micrometers pixel size is required.