Performance of rapid dual-tracer PET in canines with pre-existing tumors

Abstract

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Objectives: We are developing algorithms for processing rapid dual-tracer PET data to recover measures of interest for tumor characterization. The ability to image both blood flow and hypoxia in a single scan would enhance the study of these interrelated physiological factors, providing an improved tool for evaluating vascular status. Using dynamic imaging techniques with a short delay between injections, we have shown that tracer kinetic information can be used to recover individual-tracer signals from dual-tracer data. In this work, we have extended and refined our study of rapid dual-tracer ⁶²Cu-PTSM (blood flow) + ⁶²Cu-ATSM (hypoxia) tumor imaging in a canine model with spontaneously-occurring tumors. Methods: Four dogs with pre-existing tumors have been scanned with a rapid dual-tracer protocol that has been optimized by phantom simulations. Separate single-tracer scans were acquired for use as gold standards. Arterial blood samples were taken to measure input functions, separating freely available tracer by octanol extraction, and tissue samples were obtained for histologic analysis. The dynamic PET data were processed using a refined dual-tracer signal separation procedure to recover component single-tracer time-activity curves, which were analyzed in terms of both semi-quantitative (e.g. standardized uptake value, SUV) and quantitative (e.g. rate parameter) measures. Results: Dual-tracer time-activity curves for 44 regions on 9 tumor sites were separated into single-tracer components, and then compared to separately acquired single-tracer standards. Estimates of SUV and net uptake macroparameter for both PTSM and ATSM were strongly correlated with single-tracer results (r=0.96-0.99). Quantitative K₁ estimates were nearly identical for dual- vs. single-tracer imaging (r>0.99, slope=1.03 for PTSM; r=0.99, slope=1.05 for ATSM). Algorithms for recovering static images for each tracer are under development and show good promise. Conclusions: This canine imaging study suggests that quantitative and semi-quantitative measures of tumor blood flow and hypoxia can be obtained in 30m total using the rapid dual-tracer imaging method. This work on rapid dual-tracer PET continues to show the promise of this technique for characterizing multiple aspects of tumor physiology in vivo in a single scanning session.

Research Support (if any): ACS RSG-00-200-04-CCE