Abstract
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Purpose: To develop a new imaging methodology for assessing and monitoring the effects of therapeutic interventions in muscular diseases. We present a CT-based tissue segmentation method for determining volume and global uptake of 18F-fluorodeoxyglucose (FDG) in the thigh muscles and correlate these parameters with BMI and age. Materials and Methods:A total of 71 subjects (36 males, mean age 48 years, range 21-75) from a prospective clinical trial [NCT01724749] were included. All subjects underwent FDG-PET/CT imaging 180 min after intravenous injection of the tracer. The upper and lower boundaries of the ROI were set 5 cm below the greater trochanter and 5 cm above the intercondylar notch, respectively. Using OsiriX MD software (Pixmeo SARL, Bernex, Switzerland), a 3D growing region algorithm with a neighborhood Hounsfield unit of 1 and 150 was used to highlight the muscle. The volumes (cm3) of the left and right muscle groups were independently measured using CT-based segmentation, determined by multiplying area of the ROI with slice thickness and the FDG uptake, expressed as the average mean standardized uptake value (average SUVmean).
Results: There was no significant difference in muscle volume between the two sides: left 3606.5±1195.6 cm3, right 3633.5±1215.7 cm3, p=0.36. In contrast, a small, but statistically significant, difference was noted in the metabolic activity expressed as the average SUVmean of the two muscle groups: left 0.60±0.13, right 62±0.14, p<0.0001. Positive correlations were found between both volume and BMI (left side r=0.356, p=0.002; right side r=0.378, p<0.01) and average SUVmean and BMI (left side r=0.307, p=0.009; right side r=0.269, p=0.023). Volume decreased with age (left side r=0.362, p<0.01; right side r=0.387, p<0.01), whereas average SUVmean did not (left side r=0.171, p=0.15; right side r=0.201, p=0.09) Conclusion: The application of CT-based segmentation on FDG-PET/CT is a novel, feasible and effective method for assessing the volume and global metabolic activity of the thigh muscles. Our method addresses the need for not only structural but also metabolic assessment of muscles with possible applications in assessment and monitoring of therapeutic interventions of muscular diseases.