It is known that the Wiener spectrum obtained by one dimension scanning method depends on both the slit length of scanning aperture and the modulation transfer function (MTF) of radiographic screen-film system. Although the former has been studied and made clear by many authors, no previous work of the latter has been done. The dependence of the measured Wiener spectrum on MTF was investigated theoretically and experimentally. As the result of present work, it appears that the measured Wiener spectrum at low frequencies is under-estimated and the amount of the under-estimation increases as the resolution of the system becomes lower and its behavior can be explained by the increase of the slit length of scanning aperture necessary for accurate measurement. If physical image qualities of the systems with different MTFs are calculated by using the under-estimated Wiener spectrum, they may lead to wrong results. It is shown that comparisons between the systems must be done by using image qualities estimated by proper physical image quantities.
Although linac radiosurgery has some advantages over gamma knife, required accuracy for this purpose is very strict and extended quality assurance programs are needed. We performed phantom measurements for the accuracy of our positioning method. Tungsten balls of 4 mm diameter were assumed to be intended targets for beam concentration. Four tungsten balls were placed randomly in a head phantom made of styrene foam. The phantom was held in a base frame and a stereotactic localization box for angiogram was attached. Two orthogonal x-ray films were exposed for antero-posterior and left-right view of the phantom. The coordinates of the tungsten balls were calculated referring fiducial points on the wall of the box. Displacements of the beam center from the target were measured from the linacgraphy taken at the top and side positions of the gantry head. The targets coincide with the isocenter of the linac within 0.25 mm. However, at the top position of the gantry, relatively large displacements of the beam center from the isocenter in z direction (patient cranio-caudal direction) were observed.
We set up a server and client system with CTN server (Mallinkrodt Institute of Radiology) and personal computer (PC) client to evaluate medical image database from practical point of view. We prepared 189 CT images of a single study. The images had been stored in ACR-NEMA Ver.2 format. We transformed the image data to DICOM3 format using a batch program. The maximum number of images in a series was limited to a hundred in CTN software. On the PC client, the images were displayed in an unexpected order. The reason of the problem was that the DIC-OM3 has not a query and retrieve service for an acquisition number. It is necessary to set up a supplemental data-base system to retrieve proper images from the image server.
We investigated the traceability of the ionization chambers calibrated by the standard dosimeter with Kyushu regional center (I) for standard doses in medicine. Accuracy management of the ionization chambers of Kyushu regional center (I) has been maintained within 0.5% by intercomparison with that of the National Institute of Radiological Sciences (NIRS). The number of hospitals and the number of intercomparisons were 17 and 33 on an average per year, respectively. Accuracy of the ionization chambers of each hospital in recent years was less than 0.5% to the hospitals of 65-80% and less than 1.0% to those of 80-90%.
The data formats and the communication protocols of Digital Imaging and Communication in Medicine (DICOM) Standard are defined based on the Object Oriented Analysis (OOA) of medical images in Radiological Information Systems (RIS) or Hospital Information System (HIS). At the first step in the design of a large scale software system, it is essential to analyze the real world entities in the domain of the problem. The OOA is one of a techniques for the analysis. In the OOA, entities are depicted as objects. An object has information and acts according to the information. The 00A depicts the structural relationships among the objects, the dependency of information contained by an object on that of another object, and interactions between the objects. With the better planning in the aid of OOA, we can construct the more useful RIS or HIS. This paper reviews the basic concepts of OOA for the better use of DICOM Standard and for the better planning of RIS/HIS based on DICOM.
There are some standards in the field of the medical image exchange. This paper presents up--todate status of the digital imaging communications in medicine (DICOM) standard. The DICOM is supported by the DICOM committee in USA. Formerly DICOM was named the ACR/NEMA standard established at 1985. The ACR/NEMA standard was made for the communication of the medical images, but recently the DICOM was expanded for the storage and exchange of the media. The DICOM committee is discussing the DICOM supplements which included the radiation therapy, visible light images and digital Xray object. On the other hand, in Japan the MWH showed the technical criteria for the electronic image storage, and the MEDIS standard was published for the conformant to the MWH's criteria. A part of the DICOM standard was referred to the MEDIS standard. The DICOM standard is expected to be the key standard in the medical image informatics.
We intended to develop a system that serves all of the personal computers in a hospital with DICOM images, which are now kept in Radiology Department. In this paper, we described the development of several prototypes. Through some years of development, we found out that the World Wide Web (WWW) is suitable for our intended purpose. Finally, we developed the server that combines the DICOM and the WWW. It features useful new technology, which gives the user a preview of a DICOM image.
and its supplements to DICOM Standards Committee in USA. They proposed some supplements for Japanese language handling like S9: Multi-byte Character Set Support as additional supplements. Also they have been working to spread DICOM standard in Japan using many times like demonstration in JMCP Exhibition.