Whole-Body Perfusion Imaging with a Long Axial Field-of-View PET Scanner

Introduction In this thesis, blood perfusion was estimated and studied under both Rest condition and pharmacologically inducted Stress condition. The main objective was to explore how perfusion is affected by Rest-Stress condition in different anatomical Regions of Interest (ROIs) out of the heart, and this is the first time this is done for Rubidium. Methods Sixteen subjects without cardiac disease underwent two dynamic 82Rb PET/CT scans, the first one while patients were resting (namely Rest), the second one (namely Stress) in combination with Regadenoson, a heart-specific pharmacological stressor. Thirteen ROI masks where extracted per each patient, applying an AI tool called Total Segmentator[1] and refining them with a clustering approach based on dynamic activity inside the voxels. ROIs’ Time Activity Curves (TACs) were then extracted and fitted with a One-Tissue Compartment Model (1TCM). Thus, analysis were focused on K1, a model’s parameter related to perfusion, in order to assess how ROI, Rest-Stress condition, and time duration of the scan can influence it. In addition, a preliminary correlation-based Connectivity Analysis was performed, to investigate connections between different organs in different anatomical regions and how this could change during a pharmacologically inducted Stress condition. Results Significant differences between Rest and Stress were shown in different ROIs, namely myocardium, small bowel, colon and gluteal muscles, with a FDRcorrected[2] Wilcoxon[3] pvalue lower than 0.05. Reduced scan duration analysis showed that scan duration could be optimized according to the ROI focus: some organs, such as kidneys, gluteal muscles, pancreas, small bowel and colon, would showed a relative difference lower than 10% with a 3-minutes scan, and lower 5% with a 4-min scan. During Rest, non-trivial correlations appaired between organs like pancreascolon (R2 = 0.86) and myocardium with pancreas, stomach and glutei (R2 up to 0.73). During Stress significant couples were left-right lungs, left-right glutei and colon-pancreas, suggesting a weaker correlation in perfusion under Stress. Conclusions This study rappresents a novel investigation about how estimated K1 is highly dependant by ROI, Rest-Stress condition and other side conditions: while the myocardial response confirmed existing clinical evidence, the altered perfusion observed in abdominal organs and glutei represents a novel finding that may suggest a systemic adaptation to Regadenoson, with potential implications for the study of Coronary Artery Disease.