Total imaging process consists of radiographic, display and sensory imaging process, it is therefore difficult problem that we derivate a function evaluating the image quality of radiography, only by means of the three phisical factors (sharpness, graininess and contrast) of radiographic imaging process. Ultimately total evaluation of the image quality of radiography makes necessary applications of signal detection theory involving even human decision principle. In this study, Signal Detection Theory composed of probability, statistics and information principle is fundamentally developped for to prepare describing uniformly each process from X-ray pattern to sensory image.
In october 1975,our hospital installed the first home made computed tomography (CT) unit in Japan (Hitachi CT-250). Since then, the unit has greatly contributed to the clinical diagnosis of head lesions. Because of the prototype, however, the instrument had a number of defects which should be improved. During early period, we encountered with many troubles of unknown cause. One of the difficulties was incomplete in the unit itself. We have described various problems on maintenance of CT as the artifact originating from CT.
When we use computed tomography in clinical cases, it is important to know the slice thickness of the body displayed by computed tomography. We are informed that the unit is equiped with A and B slice with 10 mm thickness. However, it is necessary to know what layer is scanned by computed tomography. For convenience "sake" we made a computed tomographic test phantom. It was acrylate plate of 10 mm thickness. The holes, 2 mm in diameter, were made with a distance of 2.5 mm between each hole. The total thickness of this test phantom was 60 mm in piles. This test phatom was placed in the center of rotation, measuing the slice thickness. The slice thickness can be obtained by counting the number of holes in the computed tomographic image. The present results showed that the slice thickness of A was 7.5 mm for low absorption objects, and 10 mm for high absorption objects. The thickness of B slice was 10 mm for the former and 12.5 mm for the latter, respectively.
By the previous paper, we reported the new method to measurement the thickness of slice at computed tomography, discribing that each image of A and B slice in CT was not divided completely and was partially overlapped with each other. In the present paper, we studied more detailed on the problem by using a new measuring phantom, which made us to be able to measurment of the thickness of slice to multiple direction and to observe the border line of A and B slice continuously, We examined to the relation between the thickness and the tube kilovoltage and effect of different absorptive grade of the materials (Teflon, Plaxiglas and Polyethylene) on the thickness of the slice. It was founded that the higher absorptive material made the thicker slice.
Recently the computed tomography CT has become to be applied rapidly in our field. In present paper, we intended to examine the quality of image by measuring the modulation transfer functions (MTF) and studied the effects of the kilovoltage and the water bag or the air type on the quality of the CT image. For this purpose, we used the star phantom 180 mm in diamter and 45 mm in thickness which was composed of twenty four wedges of plaxiglas and the spaces of the same numbers for water. We measured the MTF form the differences in CT value between water and plaxiglas. The following results were obtained 1. The MFT value of CT was relational to the value of the tube kilovoltage. This fact showed that the more raised the tube kilovoltage made the CT image better. 2. The MTF value of CT in the air type was considerably higher than that in the water bag. This fact showed that the quality of CT image by using the air type was far superior to that by using water bag.
Since there have been reported many calculating formulas to simulate the integral dose in radiation teletherapy, there were few formulas which were enough simple and applicable in routine clinical application. Based on the interaction of gamma photon with scattering medium and the concept of energy flux, a new simulating equation, for 60-cobalt gamma ray irradiation, is considered. Integral Dose [g-rad] [numerical formula] Dd : tumor does (depth d) [rad] (μ_<en>/ρ) med : mass energy absorption coefficient (0.0295) A : field area at depth d [cm^2] Th : thickness of irradiated body [cm] The equation can be of wide application, because the error range of the value calculated by this equation to the value by integration the dose from the curve of the isodose chart is independent on the field size and the thickness of irradiated body. And it can be adaptable in moving and conformation teletherapies. When the value of average skin-rotation axis distance, average field size and average thickness of irradiated body are introduced.
70mm voiding cystogram is digitized row by row and punched out in the form of paper tape using JEC-5 small computer system and a film scanner. These digitized date are read into core memory in a 64×64 array, and written on a magnetic tape as one data per word using DP-5000 image processing system. This system is constructed of central processor TEAC-16 which has a performance of 16 kW core memory. Before extracting the boundary of urinary bladder and urethra, authors preprocessed following methods. (1) Correcting the output voltage to the relative exposure using a least squares method. (2) Eliminating the noise which is caussed by the film scanner using the digital filtering techniques. A crucial problem in using image segmentation method based on the thresholding is that of how to select the threshold. In many cases it is not possible to do this in advance, since the correct threshold may not be same for all voiding cystograms. However, it is sometimes possible to select a good threshold for each image automatically by examining the frequency distribution of gray levels.The frequency of-gray levels is constructed of the moving matrix which moves along element by element including the urinary bladder. In order to extract the urinary bladder and the urethra easily, authors reverse the digitized voiding cystogram. In the reversal image, as the urinary bladder and urethra have a maximum gray level, authors could segment the image by choosing the threshold at the 1st bottom of the valley bordering the 1st peak and the 2nd peak. In making the frequency distribution of gray levels, authors used 53×53 for the moving matrix size and used 50 for the number of gray levels.
Receiver operating characteristic (ROC) curves have been used increasingly to evaluate radiographic imaging systems in terms of observer detection performance. In this study, we evaluate radiographic screed-film combinations by d'e and the maximum image information content (I_<max>) derived from ROC curves.
From the nine health surveys made on clinical radiation technicians working at health centers during the 18 years from 1957 to 1975,679 technicians on whom blood examinations were made for not less than ten consecutive years were sampled to investigate for chronological alterations in their blood parameters. The radiation protective means at the health centers have made rapid progress ever since the atomic bomb experiment in 1954,and the dose of exposure to radiation then began to decrease. On the other hand, it was in about 1960 that the measurement of individual exposure doses began to be made on 60% of all the technicians. Chronological alterations in the average blood counts of these technicians under the abovementioned situation were such that RBC and hemoglobin level continued to increase from 1963 until about 1967,but then began to decrease, and that WBC was as low as 5,883/mm^3 in 1957,but tended to increase though slightly at each of the subsequent surveys, and was increased to 6,570/mm^3 in 1975,that is, WBC has been approaching the normal count of 6,774/mm^3 in the Japanese, with a significant difference at a not more than 1% level of significance in each survey year. For the purpose of preventing radiation hazard, further efforts should be made to protect the technicians from exposure to radiation and to control their health.