Optimization of urinary FDG excretion during PET imaging

Accumulation of fluorodeoxyglucose (FDG) activity in the urine interferes w ith the visualization of pelvic and, sometimes, abdominal abnormalities. Al though this is a major problem, there are few data on the physiological var iables affecting FDG urinary excretion that are critical to minimizing urin ary FDG interference during PET imaging. Methods: The excretion of FDG in u rine was determined during 90 min in four groups of rats (n = 24) under the following conditions: normal, hydrated, hydrochlorothiazide treated and ph lorizin treated. FDG clearance rates were measured in both normal and phlor izin-treated animals and compared with the glomeruler filtration rate measu red with Tc-99m-diethylenetriamine pentaacetic acid. We measured FDG excret ion in 10 patients who had no known renal disease and were undergoing PET s canning (divided into two groups: hydrated and dehydrated) to relate the an imal data to humans. Results: The hydrated and phlorizin-treated animals ha d the highest excretion of FDG (39.68 +/- 5.00 % injected dose (%ID) and 45 .64 +/- 9.77 %ID, respectively). Animals given the hydrochlorothiazide had the highest urinary volume, but the percentage excreted was comparable with the normal rats. Measurement of the clearance of FDG in animals before and after the administration of phlorizin determined the amount of FDG reabsor bed in the proximal tubules to be 56% +/- 9.15%. The hydrated patients had a higher excretion of FDG than dehydrated patients (16.98 +/- 1.99 %ID vers us 14.27 +/- 1.00 %ID, P< 0.021), and the volume of urine voided was signif icantly higher (P < 0.020). Conclusion: Hydrochlorothiazide increases urine volume without enhancing FDG excretion. The hydration of patients before P ET scanning may lead to more FDG reaching the bladder. Reduction of bladder activity by more frequent voiding facilitated by increased urine volume in hydrated patients may be offset by increased delivery of FDG to the bladde r. A preferable means of increasing urinary volume without increasing deliv ery of FDG to the bladder may be the use of a diuretic.