Improved discrimination of benign and malignant lesions on FDG PET/CT, using comparative activity ratios to brain, basal ganglia, or cerebellum.

PURPOSE: This study demonstrates a simple background correction method, which improves the discrimination of benign from malignant lesions on FDG PET-CT imaging, using activity ratios compared with brain, basal ganglia, or cerebellum.
METHODS: Standardized uptake values (SUVs) and comparative activity ratios (CARs) were determined for FDG uptake in 92 lesions (39 benign and 53 malignant) in 49 patients. Reference tissues included cerebral cortex, basal ganglia, cerebellum, lung, liver, and aortic blood pool. Discriminant power for each CAR was evaluated as malignant-to-benign ratio of mean uptake and ratio of intermediate-likelihood lesions to total number of lesions.
RESULTS: Uncorrected SUV varied widely for malignant and benign lesions, with considerable overlap. Ratio of mean uptake for malignant lesions versus benign lesions was lowest for uncorrected SUVAVG and SUVAVG/liver (1.92), and highest for SUVMAX/cerebral cortex (3.52). Lesions could be separated into very high (> 90%), very low (< 10%), and intermediate (> or = 10% and < or = 90%) likelihood of malignancy. The ratio of intermediate-likelihood lesions to the total number of lesions was greatest for SUVAVG (0.42) and lowest for SUVMAX/basal ganglia (0.22).
CONCLUSIONS: Ability to discriminate malignant from benign lesions was enhanced by using CARs derived from cerebral cortex, basal ganglia, or cerebellum. Using a 3-tiered diagnostic schema, most lesions could be assigned to categories of very high or very low likelihood of malignancy, with a significant reduction in indeterminant lesions, compared with uncorrected SUV.