Optimizing 18F-FDG uptake time prior to imaging improves the accuracy of PET/CT in liver lesions

Introduction: 18F-FDG PET/CT has emerged as one of the fastest growing imaging modalities. A shorter protocol results in lower target-to-background ratio, which can make identification of mildly FDG-avid lesions and differentiation of inflammatory or physiologic from malignant activity more challenging. The purpose of this study was to find the optimal time delay between radiotracer injection and imaging (TI) that would achieve a better target-to-background ratio, while maintaining adequate counting statistics to ensure scan sensitivity. Methods: Patient population-140 patients (66 male, 74 female; age 42-95) with suspicious hepatic lesions evaluated by an 18F-FDG PET scan were studied. SUV = region of interest activity/ (dose/total body weight). Results: The mean injected dose was 16.5 +/-1.8 mCi, with a mean glucose level of 107 +/26.6 (standardized to 90) mg/dl. The uptake time before imaging ranged from 61 to 158 minutes, with a mean of 108.8 +/24.8 minutes. The p-values of the correlation of SUV to time were 0.004, 0.003, and 0.0001 for malignant lesions, benign lesions, and background liver respectively. Conclusion: An approximate 90-minute window from the time of injection of 18F-FDG to PET imaging would lead to a significant improvement in targetto-background ratio, and thus more clinically valuable quantitation and more accurate visual interpretation. This benefit outweighs the minimal loss in patient throughput.