[Achievement and Philosophy of Studies on SPECT Reconstruction Algorithms].

The purpose of this article is to introduce achievement and philosophy on studies of SPECT reconstruction algorithms which Dr. Eiichi Tanaka dedicated himself to carrying out. The method that Dr. Tanaka suggested first (in 1974) was to reconstruct analytically a section image from the projection data convoluted the correction functions. The correction functions were optimized to yield a maximum 'signal-to-noise ratio'. In 1983 and 1984, two image reconstruction algorithms, WBP and RPC were suggested assuming a uniform attenuation in the object. Dr. Tanaka understood intuitively that these methods had few noise and distortions in reconstructed images. WBP was an approximate solution, but three type analytically methods were reported by Tretiak O, et al., Bellini S, et al., and Inoyue T, et al. In 1995, Metz CE, et al. and Kudo H, et al. succeeded independently each other in finishing a general theory of the analytic absorption Radon Conversion by using parameter "n". The relations among the above three analytically methods and WBP were explained, beautifully. The important thing in the study is a flexible idea such as catching a problem as the issue of black box or reverse and the result to be concise and elegant.