The yields of gamma-rays have been measured for stopping pions in water and polyethylene using a NaI detector. Nal detectors have the application to externally monitor the stopping region of negative pions within a patient undergoing therapy. Negative n mesic X-rays, r-rays and neutrons are emitted from the region at which ir mesons stop and produce stars. These radiations can be detected outside the exposed patient. A water phantom was exposed tormesons at various depths. The resulting T-ray yields were determined by counting the r-rays in coincidence with incident n mesons using a sodium iodide (Nal) detector. This type of T-ray measurement can assure that the depth-dose distribution in the patient is situated exactly at the desired location during irradiation. A direct-reading instrument such as the scintillation camera with multihole collimator is suggested as a powerful and convenient tool to ascertain the twodimensional position of the peak region in the patient.

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The DSA system installed at the kumamoto University Hospital has recently been upgraded to permit 1024 × 1024 imaging. We compare d the physical properties of digital images produced by 512 × 512 matrix and 1024 × 1024 matrix using a star pattern and a contrastdetail (CD) phantom. It was confirmed by star pattern images that the digital images o b tained by 1024 × 1024 matrix showed improvement in spatial resolution as compared with 512 × 512 matrix. According to the observation by CD phantom images the detecta b ility of simulated vessels at highdose conditions was apparently better than that obtained at lowdose conditions for both matrix sizes. DSA images obtaind with equivalent dose settings were compared for two matrix sizes. DSA images produced by the 512 × 512 matrix provided better detectability than that of 1024 × 1024 matrix when observed under same exposure settings. Clinical stuby with intraarterial D S A demonstrated that the 1024 × 1024 matrix slightly improves in the vsibility of the vessels as compared with the 512 × 512 matrix. However, in clinical image with intervenous approach no significant improvement was confirmed between two matrix sizes.

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