Tumor Blood Flow Measured by PET Dynamic Imaging of First-Pass ¹⁸F-FDG Uptake: A Comparison with ¹⁵O-Labeled Water-Measured Blood Flow

¹ University of Texas Medical School–Houston, Houston, Texas
² University of Texas M.D. Anderson Cancer Center, Houston, Texas

^* To whom correspondence should be addressed. E-mail: mullani{at}tlite.com.

	Abstract

PET molecular imaging of ¹⁵O-labeled water is the gold standard for measuring blood flow in humans. However, this requires an on-site cyclotron to produce the short-lived ¹⁵O tracer, which is cost-prohibitive for most clinical PET centers. The purpose of this study was to determine if the early uptake of ¹⁸F-FDG could be used to measure regional blood flow in tumors in the absence of ¹⁵O-water. Methods: PET scans were obtained in patients being evaluated for tumor perfusion and glucose metabolism in a phase I dose-escalating protocol for endostatin, a novel antiangiogenic agent. A 2-min perfusion scan was performed with a bolus injection of 2,220 MBq (60 mCi) of ¹⁵O-water, which was followed by a 370-MBq (10 mCi) dose of ¹⁸F-FDG. Four sequential scans of ¹⁸F-FDG uptake were acquired, consisting of an early 2-min uptake scan—or first-pass scan—and 3 sequential 15-min late ¹⁸F-FDG uptake scans. Regions of interest (ROIs) were drawn on 2 or more tumor sites and on back muscle, as a control ROI, for each patient. Arterial blood concentration was derived from the PET scans by drawing an ROI over a large artery in the field of view. Blood flow was computed with a simple 1-compartment blood flow model using the first 2 min of data after injection. Results: Blood flow estimated from the early uptake of ¹⁸F-FDG was linearly correlated with ¹⁵O-measured blood flow, with an intercept of 0.01, a slope of 0.86, and an R² regression coefficient of 0.74 (r = 0.86). The ¹⁸F-FDG tumor extraction fraction relative to ¹⁵O-water averaged 0.86. A preliminary case study of a patient with prostate cancer confirms the utility of the first-pass ¹⁸F-FDG blood flow analysis in tumor diagnosis. Conclusion: These results suggest that the first-pass uptake of ¹⁸F-FDG may provide an estimate of perfusion in a tumor within the limitations of incomplete extraction of ¹⁸F-FDG compared with ¹⁵O-water.

Key Words: PET, ¹⁸F-FDG, tumor, perfusion, blood flow, ¹⁵O, molecular imaging

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