title: Testing of local gamma-ray scatter fractions determined by spectral fitting.
abstract: The spectral-fitting method of correction for gamma-ray Compton scattering within objects separates the unscattered and scattered components of locally measured energy spectra. Here, we employ a third-order polynomial for the scattering and an approximately constant fitting window. A scatter fraction, defined as total scattered over total unscattered counts within a 20% window, is calculated for each point in our Anger camera images. These scatter fractions are tested against those from Monte-Carlo simulation for 99mTc and against results from semiconductor detector measurements for 131I. A radioactive sphere at several locations within a non-radioactive cylinder and the inverse are imaged for the testing. For one case, reproducibility of the spectral-fitting scatter fraction as a function of the number of unscattered counts within the 20% acceptance window was also determined. With 99mTc, for all cases, the agreement between spectral fitting and the standard estimation method is within 16%. With 131I, for the 'hot' sphere at two locations, the agreement is within 21%. For the 'hot' sphere at the third location (off the cylinder axis towards the camera), the dependence of scatter fraction on transverse distance is good although the absolute values are too large. Scatter fraction reproducibility is within 10% for 1000 or more counts. Therefore, further testing of spectral fitting and initial application to realistic clinical images seem to be in order.
authors.affiliation: Division of Nuclear Medicine, University of Michigan, Ann Arbor 48109.
authors.forename: K F
authors.initials: KF
authors.lastname: Koral
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: K R
authors.initials: KR
authors.lastname: Zasadny
authors.forename: N H
authors.initials: NH
authors.lastname: Clinthorne
authors.forename: W L
authors.initials: WL
authors.lastname: Rogers
authors.forename: C E
authors.initials: CE
authors.lastname: Floyd
authors.forename: R J
authors.initials: RJ
authors.lastname: Jaszczak
mesh_terms: D015902:Gamma Cameras; D005720:Gamma Rays; D006801:Humans; D007457:Iodine Radioisotopes; D009010:Monte Carlo Method; D012542:Scattering, Radiation; D013667:Technetium; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D007457:Iodine Radioisotopes; D013667:Technetium