Image quality of scintigrams is influenced by several imaging conditions. But, the relationship between image quality and diagnostic information has been not clearly evaluated. Therefore the diagnostic information was evaluated visually by radiologists using bone scintigrams changing the imaging conditions : total counts, image density, and distance from collimator to patient surface. The diagnostic information was considered the point of whether normal or abnormal scintigrams and in the abnormal scintigrams, the information of abnormal position, the abnormal area and the abnormal radioactive distribution on the bone scintigrams. Analysis of variance for the diagnostic information was performed. We concluded that using our methods the relationship between imaging condition and diagnostic informaton is analyzed quantitatively and the base of imaging technique is evaluated objectively.
An attempt was made to reduce the background counting rate of γ-ray spectrometer commonly used. Additional setting of an inner shield made of oxygen free copper within the ordinary shield was found to work well. Remarkable reduction of spectral lines from radondaughters was observed by introducing N2-gas into the sample chamber to expel Rn together with the daughters existing there. Fluctuation in background also diminished sufficiently and was stabilized. It may be possible to employ the spectrometer of common use, even not to be designed for the low-level counting, for the measurement with high stability of low level radioactivity usig the present simple technique.