Zhejiang Univ, Dept Life Sci & Biomed Engn, Hangzhou 300072, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China
; Zhengzhou Univ, Zhengzhou 450052, Peoples R China
In this article. a direct method to reconstruct images from projections is presented. This method, having its origin in astrophysics to restore images from observed data, uses a constant upper bound and a variable lower bound to constrain the maximum and minimum values taken by the emission intensity during iteration. Computer-simulated emission projection data from two phantoms are used for reconstruction. Comparison is made with other methods. The results show that a much better spatial resolution can be acquired by this method, especially for the sharp-shaped emission sources. (C) 1999 John Wiley & Sons, Inc.