Clinical evaluation of direct 4D whole-body PET parametric imaging with time-of-flight and resolution modeling capabilities

Abstract

Whole-body (WB) PET parametric imaging has recently become clinically feasible with the introduction of multi-bed dynamic acquisition protocols, benefiting from the latest technologies in clinical PET scanners. Currently, Time-of-Flight (TOF) capabilities of modern PET systems allow for more accurate localization of the annihilation position along the line of response (LOR). As a result, TOF can prevent propagation, during image reconstruction, of various resolution degrading factors and noise beyond their origin and across the image space, thus providing i) an inherent correction or contrast recovery mechanism and ii) an effective sensitivity gain relative to non-TOF acquisitions. In addition, the incorporation of the PET system's point spread function (PSF) within the reconstruction system matrix has resulted in i) enhanced contrast and ii) considerably lower image roughness. Recently, we explored the effect of TOF and PSF on WB indirect Patlak imaging. In this work, we systematically investigate the additional benefit of TOF and PSF on clinical studies when reconstructing WB Patlak images directly from projection data. Therefore, we developed a nested direct 4D Patlak WB reconstruction algorithm capable of i) utilizing TOF information, ii) modeling PSF with an effective space-invariant Gaussian resolution kernel and iii) supporting both standard and generalized Patlak analysis. Our clinical evaluation on a set of WB dynamic clinical studies, as acquired with Siemens Biograph mCT TOF scanner, indicated a 15–30% target-to-background (TBR) and contrast-to-noise ratio (CNR) enhancement in all examined regions and for both Patlak methods, when only TOF feature is enabled, with an additional 5–10% improvement when combined with a 4mm FWHM Gaussian PSF kernel. Thus, we have demonstrated the benefits of integrating TOF and PSF features within a clinically adoptable direct 4D WB generalized Patlak reconstruction scheme.