It is very important for the proton therapy to detect the transmission length of oroton beam in a patient's body to verify the irradiated field. We measured activities of positron-emitters in water and MiX -DP bombarded by proton beam (experimental irradiation conditions; dose rate: 5cGy/min, dose: lGy). As a result of this experiment, it was suggested that it was possible to estimate the transmission length of protons from the depth-activity distribution in the region of depth deeper than the maximum activity depth, which decreased exponentially with depth. The activities in water and MiX DP immediately after bombarment by protons with an energy of about 130 MeV were about 1.6kBq/g and 1.2kBq/g, respectively. Immediately after bombarment, the main sources of the activity were 15O and 11C.

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A hot-cathode flash x-ray generating system driven by an oscillation- type high-voltage pulser has been studied for testing an availability in the biomedical application.
The essential parts of the system are a negative high-voltage pu lser with a trigger device, an x-ray tube and a DC supplier for heating a filament of the tube. The high-voltage pulser is composed of an oscillation pulser with two ceramic condencers and a coil. A doubled high-voltage is provided by inverting a polarity of one of the two charged condensers connected in series by a trigger of air-gap spark.
In the present work, the tube voltage is nearly equal to the pulser output, even if the tube current flows in the x-ray tube. The tube voltage is, therefore, about 1.4 times the charged voltage and its maximum is about 100kV with the maximum tube current of 0.75A. An effective duration of the oscillating voltage is less than 7 ps and the repetition rate of the pulser output attains to about 100Hz. Under the charged voltage of -70kV, the maximum x -ray intensity is about 72.1 nc / kg per pulse at the distance of 0.5m, and the focus spot is of 3.0 x 4.0mm in size.
The values of floating capacity and resistivity are also estimated from the observed da mped oscillating from of the pulser output.

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The history, the present status of the art and the future of the research and development activities of PACS in the world as well as here in Japan are reviewed and discussed. Themes of research and development on PACS which are appropriate to radiological physicists are listed and explained. They are in the field of physics, computer sciences, mathematics and engineerings. Three typas of approach attitude to these themes by physicists are described, and classification of these themes are tried.
The another emphasizes the significance of the role of radiological physicists in researc h, development, implementation and operation of PACS, by raising concrete examples of fruitful activities of researchers. The leadership to medical doctors, radiological technologists and manufacturer's engineers are expected to be taken by radiological physicists.
specific items of research such as ima ge data compression algorithm, image quality analysis, neural network application are of course candidates of leadership taken by radiological physicist. But integrated research projects should be organized and performed by them in large scaled field such as technology assessemet. Very concrete and qnantitative analysis of measured data to verify effectivenees of PACS will be highly appreciated by fudget controling government officers as well as medical doctors in hospitals.

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We are developing a scheme of computer-aided diagnosis (CAD) which refers to a diagnosis made by a radiologist who takes into consideration the results of an automated computer analysis of radiographic images. The general approach is to alert the radiologist by indicating potential lesion sites and/or by providing objective measurements of normal and abnormal patterns. In this study, we demonstrated the current results fo our computerized automatic analysis for (1) the identification of lung nodules and pneumothoraces, and the assessment of cardiomegaly and interstitial disease in chest radiography; (2) the identification of clustered microcalcifications and masses in mammography, and (3)the assessment of stenotic regions in angiography. In addition, the basic scheme of lung texture analysis for assessment of interstitial diseases was presented, and the effects of digital parameters in digitization of chest images on the results of the lung texture analysis was discussed. Preliminary results obtained with CAD from various radiographic examinations are very encouraging. However, CAD is still at an early stage of its development. It will be necessary to increase further understanding of image features of normal and abnormal patterns, and to establish large databases. We believe that CAD will become a reality in the near future.

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Recent status of advanced science, technology and engineering on PACS is reviewed. Due to the motion for computer " downsizing", many PACS related key components have been enormously advanced. Giga level components, such as giga bit IC memory, giga instruction per second (GIPS) MPU chip, giga bit per sec. (Gbps) transmission etc. have been/will be available. The second generation PACS will be constructed soon on the base of these advanced techonologies.

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In this second half, postgraduate education in the United Kingdom and physics teaching for diagnostic radiology residents in the U. S. A. are described. Departments and research facilities in Japanese medical schools relating to medical physics are reviewed. The purpose, significance, potentialities of medical physics education in Japan are discussed.

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