Feasibility of dual phase 99mTc-MDP SPECT/CT imaging in rheumatoid arthritis evaluation

Abstract

Objectives To prospectively demonstrate the feasibility of performing dual-phase SPECT/CT for the assessment of the small joints of the hands of rheumatoid arthritis (RA) patients, and to evaluate the reliability of the quantitative and qualitative measures derived from the resulting images. Methods A SPECT/CT imaging protocol was developed in this pilot study to scan both hands simultaneously in RA patients, in two phases of 99mTc-MDP radiotracer uptake; namely the soft-tissue blood pool phase (within 15 minutes after radiotracer injection) and osseous phase (after 3 hours). Joints were evaluated qualitatively (normal vs. abnormal uptake) and quantitatively (by measuring the maximum corrected count ratio [MCCR]). Qualitative and quantitative evaluations were repeated to assess reliability. Results Four participants completed seven studies (all four were imaged at baseline, and three of them at follow-up after 1-month of arthritis therapy). A total of 280 joints (20 per hand) were evaluated. The MCCR from soft-tissue phase scans was significantly higher for clinically abnormal joints compared to clinically normal ones; p<0.001, however the MCCR from the osseous phase scans were not different between the two groups. Intraclass Correlation Coefficient (ICC) for MCCR was excellent (0.9789, 95% confidence interval [CI]: 0.9734-0.9833). Intra-observer agreement for qualitative SPECT findings was good for both the soft-tissue phase (kappa=0.78, 95%CI: 0.72-0.83) and osseous-phase (kappa=0.70, 95%CI: 0.64-0.76) scans. Conclusion Extracting reliable quantitative and qualitative measures from dual-phase 99mTc-MDP SPECT/CT hand scans is feasible in RA patients. SPECT/CT may provide a unique means for assessing both synovitis and osseous involvement in RA joints using the same radiotracer injection.