Abstract
2221
Introduction: Compared to standard semiquantitative analysis of PET data using standardized uptake values (SUVs), tracer kinetic analysis may yield improved contrast versus blood, more robust quantitative parameters, and more reliable characterization of systems biology in the context of atherosclerosis imaging using positron emission tomography. To date, whole-body PET is usually performed using a static imaging approach, in which multiple bed positions are acquired sequentially and subsequently merged to obtain an expanded axial field of view. Here, we introduce a novel dynamic whole-body positron emission tomography (PET) protocol that is enabled by rapid continuous camera table motion, followed by reconstruction of parametric datasets using voxel-based Patlak graphical analysis. We hypothesized that parametric images from dynamic whole-body PET will more clearly separate vessel wall from blood and other background signal, improving vessel wall contrast, lesion visualization, quantification, and characterization of systems-based organ interactions.
Methods: We prospectively enrolled 25 subjects. Subjects underwent dynamic PET up to 90 min after injection of 309.1±13.2 MBq of 2-[18F]fluoro-2-deoxy-D-glucose (FDG) on a Siemens Biograph mCT 128 Flow PET/CT scanner (Siemens Healthineers, Knoxville, USA) equipped with a magnetically driven table optimized for continuous scanning. Two sets of images were generated: (i) The established standard of static standardized uptake value (SUV) images, and (ii) parametric images of the metabolic rate of FDG (MRFDG) using Patlak plot-derived influx rate. Arterial lesion detectability and reader confidence were evaluated by 4 independent readers, and compared. Arterial wall signal was measured (using arterial maximum SUVs and target-to-background ratios (TBRs)) and compared using volume-of-interest technique, and its association with hematopoietic and lymphoid organ signal (i.e., spleen, lymph nodes and bone marrow) and atherosclerotic risk factors was explored.
Results: Parametric MRFDG images provided excellent arterial wall visualization, with elimination of blood-pool activity, enhanced focus detectability and reader confidence. Visual lesion detectability improved in parametric MRFDG over SUV images (mean of differences, 0.94 (95% CI, 0.77 to 1.10); P<0.0001). Quantitative analysis revealed that target-to-background ratio (TBR) from MRFDG images was significantly higher compared to SUV images (2.6±0.8 vs 1.4±0.2, P<0.0001), confirming improved arterial wall contrast. Regarding multi-organ crosstalk, MRFDG images revealed significant associations between arterial wall signal and activity of spleen (P=0.0009), lymph nodes (P=0.0055) and bone marrow (P=0.0202), whereas standard SUV PET images only identified the correlation with spleen signal (SUVmax, P=0.0067; TBRmax, P=n.s.). Finally, arterial wall signal on MRFDG images increased with the number of atherosclerotic risk factors (r=0.49 (95% CI, 0.11 to 0.74), P=0.0138), where signal from SUV images (SUVmax, P=0.9754; TBRmax, P=0.8760) did not.
Conclusions: We demonstrated the feasibility of whole-body parametric PET imaging for absolute quantification of arterial wall metabolic rate of FDG. Parametric images provide superior arterial wall contrast, and they are better suited to explore the relationship between arterial wall activity, systemic organ networks and cardiovascular risk. Parametric whole-body imaging may improve the characterization of the biology of arterial wall disease in future diagnostic studies and clinical trials exploring the pharmacologic modification of disease activity.