© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. The current standard of care for treating rheumatoid arthritis (RA) involves early use of disease modifying antirheumatic drugs (DMARDs). Nevertheless, 30% of RA patients still fail their first DMARD and it takes 3-6 months to detect treatment failure with current monitoring methods; this places patients at a higher risk of irreversible joint damage. We previously developed a dynamic contrast-enhanced time-resolved near-infrared spectroscopy technique (DCE TR-NIRS) for quantifying joint blood flow (BF). We now aim to investigate whether joint BF, as measured with DCE TR-NIRS, can be used to monitor disease activity and treatment response in a rat model of RA. Arthritis was induced in 4 adult male Lewis rats using the well-established adjuvant-induced arthritis model. Baseline measurements were acquired prior to adjuvant injection on day 0. Arthritis progressed until day 20 ("Pre-Treatment" phase), after which rats received DMARD treatment (Enbrel®: 0.5 ml/kg; intramuscular injection) once every 5 days ("Treatment" phase). Starting on day 0, ankle joint BF was measured every 5 days until the end of the study on day 40. Mean rat ankle joint BF (mL/min/100g) increased from 7.94±3.71 at baseline to 15.77±4.58 during the Pre-Treatment phase. Following treatment, mean joint BF decreased to 12.15±1.82 mL/min/100g. This is an ongoing study and the preliminary results shown here suggest that joint BF measured with DCE TR-NIRS is sensitive to RA disease activity and could detect response to treatment.