Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.

Novel PET/MR Fusion Imaging and Quantification of Knee Synovitis in Rheumatoid Arthritis.

Ryan4,  John T., Ng1,  C. T., Kennedy2,  Aisling, Gibney1,  Robert G., Fitzgerald1,  Oliver, Brennan5,  Patrick C., Heffernan1,  Eric

Dublin Academic Medical Centre, Dublin, Ireland
Dublin Academic Medical Centre
University College Dublin
University of Sydney, Lidcombe, NSW, Australia
University of Sydney

We recently identified hypoxia and altered blood vessel stability in the rheumatoid arthritis (RA) joint suggesting the vessels are dysfunctional, as they do not match metabolic demand. PET/CT imaging is recognized as an important advance in health care and research. In this study we aim to develop an innovative imaging approach to visualize and quantify synovial tissue (ST) blood flow and metabolic activity in inflamed joints of RA patients.

RA patients with an active knee joint synovitis were recruited and underwent clinical assessment prior to contiguous imaging initially with MR, then PET/CT followed by a needle videoarthroscopy, ST biopsy and pO2 measurement (novel LICOX probe). The PET radiotracer - Fluorodeoxyglucose (18F) was used and image-data intensity resolution was optimised for ST. These images exhibit the qualities of MRI with higher intensity regions in the areas of ST inflammation with extra heat-map information from the PET imaging. Semi-quantitative scoring of the MRI datasets was performed using the RAMRIS score. ST biopsies were stained for CD3+ (T cells), CD68+ (macrophages), and Factor VIII/ SMA (Blood vessel maturity) and NCAM expression.

Figure 1. (a) Axial CT slice, (b) Axial PET/CT, (c) Axial contrast-enhanced MRI, (d) PET/MR fusion image.

RA patients (n=9) have completed combined scanning/arthroscopy protocols. Proof-of-concept images and quantitative assessments have been developed (Fig. 1, 2). Fig. 1a and b show the CT and PET/CT scans, 1c shows MR and the PET/MR fusion image is shown in Fig 1d. Evaluation of disease activity, blood flow or metabolic activity is not possible in Fig 1a or 1c, while Fig. 1b only provides information of metabolic activity. Fig. 1c does illustrate areas of high signal representing inflammation. Fig. 2 shows the contrast of PET imaging of an inflamed knee compared to the uninflamed contralateral knee and good PET/MRI structural agreement. A region of interest (ROI) was evaluated (n=3) of the target and the opposite knee to calculate a ratio of affected:unaffected. A significant correlation was found between PET activity with MRI score (r = 0.9986, p < 0.0001), with low tpO2 in vivo levels (xyz), while an inverse relationship was found with blood vessel maturity and stability, reflected by factor VIII/ SMA and NCAM expression on ST immunohistology of the blood vessels (r =-0.99, p < 0.0001).

Figure 2. PET image of affected side versus unaffected contralateral side (top). Structural agreement of PET with MRI (bottom).

This is the first description of hybrid PET/MRI fusion imaging of inflamed joint in RA. The preliminary data suggest a close correlation between measures of inflammation, blood flow and metabolic activity. The potential correlation with cellular and molecular biomarkers suggests this novel imaging protocol may be extremely powerful in assessing response to therapies in vivo.

To cite this abstract, please use the following information:
Ryan, John T., Ng, C. T., Kennedy, Aisling, Gibney, Robert G., Fitzgerald, Oliver, Brennan, Patrick C., et al; Novel PET/MR Fusion Imaging and Quantification of Knee Synovitis in Rheumatoid Arthritis. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1625
DOI: 10.1002/art.29391

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