[IEEE 1999 IEEE Nuclear Science Symposium. Conference Record. 1999 IEEE Nuclear Science Symposium and Medical Imaging Conference - Seattle, WA, USA (24-30 Oct. 1999)] 1999 IEEE Nuclear Science Symposium. Conference Record. 1999 Nuclear Science Symposium and Medical Imaging Conference (Cat. No.99CH37019) - Simultaneous estimation of SPECT activity and attenuation distributions from measured phantom data using a differential attenuation method