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Attenuation correction is necessary for the reconstruction of SPECT images. One report has mentioned that attenuation correction by X-ray computed tomography (CT) is effective for a non-uniform attenuation body. We examined the effect of attenuation correction on SPECT images by changing the scanning conditions of CT, and evaluated the possibility of attenuation correction by low-dose CT. The phantom was scanned under several X-ray tube conditions varying from 80 kV to 135 kV and from 7.5 mAs to 200 mAs. We obtained equations of attenuation correction based on the Hounsfield Unit (HU) units of each pixel and compared the effects of attenuation correction. The results showed that the equation for attenuation correction under each condition did not vary significantly, and the effects of attenuation correction by the equations did not vary significantly between CT of low dose and that of clinical dose. This result suggest that the attenuation correction obtained by low-dose CT was equal to that obtained by the clinical dose. In conclusion, it seemed that the equation and map of attenuation correction matched with each radionuclide yielded more adequate attenuation correction than conventional methods.

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Following 4 items were investigated for standardization of the ability and imaging of the scinti − camera ， the historical backgrQund of the ability ・ improvement with the analog type scinti − camera and the digital type scinti − camera with the correction system ． the eva ！ uation of uniformity of the analog type scinti ・ camera ． the paramaters (LSF ， MTF) which has much hnfluence on the lneasurement of the scinti ・ camera resolution ． the sensitivity of the collimator and the evaluati 。n of the noise ． Result ： the historical background of the scinti ・ camera suggested the necessity of establishing a standard for the ability evaluation of the digital type scinti ・ camera 、(1) It is necessary to study further the characteristics of the single and multi − energy spectrums ， and to establish new standards for uninformity evalution ， in addition to the NEMA and the JRT standard ．(2) Sampling theory plays a great role in the evaluation of the resolution measurement ， because it is influenced by the sampling interval and the peak counts of LSF ．(3) finally ， Wlth regard to the collimator − sensitivity alld the noise evaluation ， it is necessary to evaluate the noise by the wiener − spectrum method in addition to the FWHM and MTF methods ．(4)