For measurement of MTF of screen-film systems with a square wave chart, manual determination of maximum and minimum densities from the output of a microdensitometer is needed. However, manual determination may sometimes lead to errors. Therefore, the aim of this work is to develop a method of calculating the maximum and minimum densities of a chart image by computer. In this paper, the finite Fourier series with minimum AIC (Akaike Information Criterion) is introduced to approximate the density distribution data, and the maximum and minimum density values are determined by the finite Fourier series. The square wave response function (SWRF) is then computed from the characteristic curve. The results showed that SWRF obtained by the finite Fourier series method accorded well with SWRF obtained by manual measurements over the whole spatial frequency range.
Stereoradiographs have features of high spatial and high temporal resolution as an examination for blood vessels, and give us useful internal geometrical information. However, viewing point is fixed to the point of X ray source, so that radiologists perceive depth with the technique of “cross eyed stereoscopy” in general. We are studying 3D reconstruction using a pair of stereoradiographs in order to observe from any direction and obtain geometrical information. In this paper, we described a method of geometrical determination and an edge feature extracting procedure for finding correct binocular correspondence. The edge feature extracting procedure is modeled the procedure to find binocular correspondence on the visual nervous system. The procedure can be classified into 2 main processes.1) The contrast enhancement process; original images are convolved with difference of two Gaussians (DOG) operator. The DOG operator has a characteristic of a small central excitatory part and a larger inhibitory region that extends over the entire 11 by 11 receptive field.2)The edge features extracting process; the contrast enhanced images are convolved with operators that have a sensitivity of specified direction. Using these results as excitatory input and inhibitory input over the receptive field, direction and position of edge are recognized by processing with the “shunt” characteristic. We also investigated relation between spatial resolution and pixel size. Finally, we presented examples of automatic 3D reconstruction using stereoradiography.
In order to assess the PME constituents on 31P in vivo MR spectra with unresolved PME peak, we developed a method to manipulate the chemical shift of PME and pH. This method was applied to spectra from 14 malignant extremity tumors, and the results were consistent with high resolution NMR data appeared in previous literature. This analytical method might make an good estimation of the major constituents of the PME peak in case a decoupling technique is not available for in vivo spectroscopy.
The wobbler method is not applicable to strongly bunched beams, though it has superiority in the adjustment of the size of irradiation field. In this short note, the author propose an alternative method of beam broadning utilizing a co axial electric current. The technological feasibility of the method is also discussed briefly.
Quality assurance (QA) system in modern radiotherapy has been established in the United States early in the 1990's followed by European countries. In Japan, similar research started only several years ago, especially in clinical aspect. QA system includes three major categories; namely, structure, process and outcome. Modern radiation therapy is so complex that close relationships among radiation oncologists, medical physicists, radiation technologists, nurses are essential and their responsibility should be clarified. This article reviewed recent advances in QA system in the U. S. and Europe and referred to several QA programs in Japan and Gunma Prefecture.
There has been a great advancement in the technique and practice of mammography since the 80's. Briefly reviewed are recent development of mammography technique and brast cancer screening in Europe and North America, including American College of Radiology (ACR) Mammography Accredition Program, and Mammography Quality Standard Act (MQSA), as well as activities in this area in Japan such as publication of Mammography Quality Control Guideline by Japan Radiological Society. Importance of quality control and a team work aproach in establishing high quality mammography is stressed with cooperation of medical physicists, radiologists and other health professionals.
The image quality of mammogram has improved over the past 2 decades as a result of the development of specially designed mammography unit. For mammography to achieve high sensitivity and specificity, all aspects of the imaging process must be optimized. This paper describes the recent development in breast imaging technologies, including design of the x-ray equipment (traget and filtration materials), detector (screen-film system), and processing used for mammography. The methods for acceptance testing and quality control on mammography have been also reported.
Facilities, which perform mammographic screening, must ensure high quality mammograhic examination of patients and minimize the risk due to patient dose. To obtain high-resolution, high-contrast, low-dose images in mammography, it is necessary to use dedicated X-ray equipment which meets the quality requirements of mammography, to optimize technique factors concerning image recording system and processing patient positioning and bresat compression, and to implement routine check and periodic quality control to maintain these optimum conditinne
Radiation exposure to a patient should be kept as low as possible, yet the image quality of radiograph is dependent on the radiation dose. There must be some trade off between the image quality and the exposure dose. In the case of mammography, mammary gland is highlty sensitive to radiation, the above statement is especially important. Actual diagnostic dose may depend on such factors as technique, equipment and facility. One important aspect of the quality control of mammography is the standardization of dosimetry. Here in an effort to make protocol of dosimetry, some problems associated with the standardization of dosimetry are discussed with reference to articles.
Breast cancer is the most prevalent cancer among women in the U. S., with over 175,000 new cases and 45,000 breast cancer related deaths occurring annually. Mammography Quality Standards Act of 1992 (MQSA) was enacted to establish uniform, national quality standards for mammography quality assurance. Key elements of the MQSA are the requirements of each facility to (a) obtain accreditation by an FDA approved accrediting body, (b)meet quality standards for personnel, equipment, and quality assurance, (c) employ regular quality control practices including performance of an annual survey by a qualified medical physicist, (d) document compliance with MQSA requirements, and (e) undergo annual inspection. ACR program serve as the model for the statutory accrediting body. A 21 question survey prepared by the ACR was sent to most medical physicists who perform evaluations of mammographic units.510 physicists said that they will meet 1996 qualification guidelines of certification. A sufficient number of certified medical physicists will be available to provide required annual performance evaluations of all mammography units in the U. S.. It is the problem that Japan and U. S. are extermely different in the number of medical physicists.