%0 Journal Article %A Sergey Shcherbinin %A Anna Celler %T Towards absolute quantitation of activity distribution in SPECT-CT cardiac studies %D 2008 %J Journal of Nuclear Medicine %P 396P-396P %V 49 %N supplement 1 %X 1667 Objectives: In this phantom study, we investigate the accuracies of the absolute activity distributions in the heart that may be achieved when using different acquisition protocols and reconstruction algorithms. Methods: A series of thorax phantom scans without and with two large active water bags was performed on SPECT-CT GE Infinia-Hawkeye system. Data collected in 120 views with 128*128 matrix and circular 360 degrees rotation (120/360) was reshaped to model three acquisition protocols (60/180, 120/360, and 60/360). CT-based attenuation correction (AC) and resolution recovery (RR) were incorporated into system matrix of OSEM algorithm (10 subsets, 2-50 iterations). Scatter component (SC) calculated using Analytical Photons Distribution (APD) method was included into the forward step. The reconstructed images were scaled to get absolute activities. No partial volume (PV) effect correction was used. Results: The total activity in the heart monotonically increased with the number of iterations and after 50 iterations the following accuracy values (in a percentage of truth) were achieved: 52-59% (normal phantom, no SC), 44-46% (large phantom, no SC), 60-68% (normal phantom, with SC), 55-56% (large phantom with SC). While total activity practically does not depend on the acquisitions protocol, the heart uniformity was slightly better for 120 than for 60 stops. In some experiments with large phantom, false perfusion defects were visible, their severity decreased with increasing number of iterations. Conclusions: Using 128*128 acquisition matrix and AC+SC+RR, total absolute heart activity reaches 60-70% accuracy level after 50 OSEM iterations. For large phantoms, this value is lower but more iterations might improve reconstruction accuracy and uniformity of the heart image. Further improvements could be made when PV effects are taken into account. %U