18F-FDG-PET/CT in measuring volume and global metabolic activity of thigh muscles: a novel CT-based tissue segmentation methodology.

Purpose We present a novel computed tomography-based tissue segmentation methodology for determining volume and global uptake of FDG of the thigh muscles and correlate these parameters with age. Materials and methods A total of 71 subjects from a prospective clinical trial (NCT01724749) were included. PET/CT scans were acquired 180 minutes after intravenous injection of FDG. A 3D growing region algorithm with neighborhood Hounsfield unit threshold between one and 150 was used to highlight the muscle. FDG uptake was expressed as the average mean standardized uptake value normalized for lean body mass (average SULmean). Femur volume was used to normalize thigh muscle volume to calculate normalized volume and correlate with age. Results We found a significant negative correlation between normalized volume and age (left side r = -0.262, P = 0.02; right side r = -0.286, P = 0.01). No statistically significant difference was found between SUL and age or between SUL and BMI. There was no statistically significant difference in muscle volume on the two sides. Statistically significant difference was noted in the global metabolic activity (SUL) between the two sides (left 0.39 +/- 0.06, right 0.42 +/- 0.08, P < 0.001), with 56/71 (78.8%) subjects having higher uptake on the right side. Conclusion FDG-PET/CT using CT-based segmentation is a novel imaging modality assessing the volume and global metabolic activity of the thigh muscles. It could be possible to utilize this methodology for the research and understanding of lower limb muscle pathophysiology.