R. Clack Gengsheng L. Zeng Y. Weng P. E. Christian Grant T. Gullberg Cone Beam Single Photon Emission Computed Tomography Using Two Orbits. 45-54 1991 conf/ipmi/1991 IPMI db/conf/ipmi/ipmi1991.html#ClackZWCG91 http://dx.doi.org/10.1007/BFb0033741