Spectral Factor Analysis for Multi-isotope Imaging in Nuclear Medicine

In nuclear medicine, simultaneous dual-isotope imaging is used to determine the distribution of two radiotracers from a single acquisition and for emission/transmission (E/T) imaging in SPECT. However, no general solution to the cross–talk problem caused by scattered and unscattered photons has been found yet and accurate quantification cannot be performed. We describe a general method of spectral factor analysis (SFA) for multi–isotope acquisitions. SFA corrects for cross–talk due to unscattered and scattered photons in planar or SPECT imaging involving two or more radiotracers and for E/T scans. A Tc-99m/I-123 phantom study shows that quantitative accuracy is within 10% with SFA, while errors up to 170% are observed using conventional spectral windows.