Global assessment of PET tracer uptake in joints using CT segmentation: a novel approach to quantify global metabolic activity.

Objectives: 1. Highlight the indications of PET imaging in benign joint disease joint disease.2. Discuss the relevant radiopharmaceuticals (FDG and NaF) for use in benign joint diseases.3. Present a novel method to quantify the global metabolic activity using CT segmentation.

Methods: We are presenting a CT based segmentation method allowing the quantification of tracer uptake in different compartments of the joint based on Hounsfield units (HU) as measured on fused PET/CT images. Joints are mainly formed by the articulation of bones (trabecular and cortical), cartilage, synovium and ligaments. In this methodology, we will use OsirX MD v.9.0 (DICOM viewer and image-analysis program, Pixmeo SARL; Bernex, Switzerland) to manually draw regions of interest depending on predetermined anatomical landmarks and setting an upper and lower HU threshold to quantify metabolic activity of different joint compartments. A score for the global metabolic activity of the joint will be measured for each subject.

Results: FDG is a sensitive tracer allowing the quantification of metabolic activity of focal lesions, synovium and bone marrow. NaF also allows the quantification of bone turnover in joints and focal lesions. Osirix MD measures SUVmean, SUVmax, global SUV and volume of the ROI. Conclusion: FDG PET and NaF PET are both highly sensitive tracers for detecting and quantifying the metabolic activity of joint disease manifestation. PET is not the first line imaging modality in the evaluation of joint diseases, but this methodology will lead to more standardized and reproducible techniques for measuring global disease activity using PET. These techniques could be utilized for studying pathophysiology of joint diseases and monitoring treatment-response.