• PET imaging provides functional parameters of (18) F-FDG-positive lesions, such as SUVmax and SUVpeak. • Averaging SUV from several hottest voxels (SUVmax-N) is a further SUV metric. • Variability of SUVmax-N is significantly lower than SUVmax and SUVpeak variability. • SUVmax-N should improve SUV accuracy for predicting outcome or assessing treatment response. • An optimal total hottest volume should be determined through further prospective studies.
This work investigated whether 18 F-FDG PET standardized uptake value (SUV) is stable over time in the normal human liver. Methods: The SUV-versus-time curve, SUV(t), of 18 F-FDG in the normal human liver was derived from a kinetic model analysis. This derivation involved mean values of 18 F-FDG liver metabolism that were obtained from a patient series (n 5 11), and a noninvasive population-based input function was used in each individual. Results: Mean values (695% reliability limits) of the 18 F-FDG uptake and release rate constant and of the fraction of free tracer in blood and interstitial volume were as follows: K 5 0.0119 mLÁmin 21 ÁmL 21 (60.0012), k R 5 0.0065Ámin 21 (60.0009), and F 5 0.21 mLÁmL 21 (60.11), respectively. SUV(t) (corrected for 18 F physical decay) was derived from these mean values, showing that it smoothly peaks at 75-80 min on average after injection and that it is within 5% of the peak value between 50 and 110 min after injection. Conclusion: In the normal human liver, decay-corrected SUV(t) remains nearly constant (with a reasonable 62.5% relative measurement uncertainty) if the time delay between tracer injection and PET acquisition is in the range of 50-110 min. In current clinical practice, the findings suggest that SUV of the normal liver can be used for comparison with SUV of suspected malignant lesions, if comparison is made within this time range.
This work addresses the issue of using 18 F-FDG PET in patients with renal failure. Methods: A model analysis has been developed to compare tissue 18 F-FDG uptake in a patient who has normal renal function with uptake in a theoretic limiting case that assumes tracer plasma decay is tracer physical decay and is trapped irreversibly. Results: This comparison has allowed us to propose, in the limiting case, that the usually injected activity be lowered by a factor of 3. We also proposed that the PET static acquisition be obtained at about 160 min after tracer injection. These 2 proposals were aimed at obtaining a similar patient radiation dose and similar tissue 18 F-FDG uptake. Conclusion: In patients with arbitrary renal failure (i.e., between the 2 extremes of normal function and the theoretic limiting case), we propose that the injected activity be lowered (without exceeding a factor of 3) and that the acquisition be started between 45 and 160 min after tracer injection, depending on the severity of renal failure. Furthermore, the model also shows that the more severe the renal failure is, the more overestimated is the standardized uptake value, unless the renal failure indirectly impairs tissue sensitivity to insulin and hence glucose metabolism.
It is recommended that dual-time-point 18F-FDG-PET imaging is not indicated to differentiate between malignant and benign pulmonary lesions, whose size and maximal SUV are greater than 10 mm and 2.5, respectively. Furthermore, a model analysis suggests that the variation in SUV observed between early and delayed scans may be explained by different values of the 18F-FDG release/uptake ratio.
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