A derivative-free, two-dimensional equiangular fan-beam reconstruction form
ula for a noncircular scanning locus is derived under three practical condi
tions. The formula contains the same terms as the traditional formula, exce
pt that the constant source-to-origin distance is replaced by the source-to
-origin distance as a function of the rotation angle. The correctness of th
is formula is tested in numerical simulation. The potential applications of
the formula include fourth-generation CT, electron-beam CT, SPECT, and x-r
ay microtomography. (C) 1999 Society of Photo-Optical instrumentation Engin
eers.