Strategies for accurate attenuation correction with single photon transmission measurements in 3D PET

3D PET systems benefit from using single photon sources for transmission measurements as this reduces dead time and improves the photon flux, and therefore the signal-to-noise ratio, in the attenuation (CL) correction data. However, uncollimated point source measurements will include a large (~50%) scatter component which biases the μ values. No single approach will necessarily be able to mitigate against this for different scanning scenarios. The authors have investigated five approaches to scatter removal and/or correction using a ¹³⁷ Cs source for transmission data: (i) rescaling the measured data, (ii) energy window methods, (iii) restricting the polar acceptance angle (θ), (iv) collimating the source (ECAT ART only), and (v) segmentation and reassignment with expected μ values. The results indicate that physical collimation of the ECAT ART point source and segmentation on the fixed ring EXACT 3D produce quantitatively useful data