Magnetic resonance imaging and spectroscopy of the periarticular inflammatory soft-tissue changes in experimental arthritis of the rat.

Arthritis was induced in rats by intradermal injection of Freund's complete adjuvant. MRI was performed with a resistive imager operating at 0.35 T. A spin echo (SE) technique with TR = 0.5 and 2.0 seconds, TE = 28 and 56 msec was used. Transaxial images of hindpaws and knees were obtained at different times after injection of adjuvant. In vitro proton spectroscopy of normal and arthritic hindpaws was also performed. Histologic confirmation was obtained in each case. Inflammatory soft-tissue lesions were seen as focal areas of high intensity on spin echo images obtained with TR = 2.0 seconds and TE = 56 msec and were characterized by long T1 and T2 relaxation times and high spin density. In comparison with both conventional radiography and physical examination, early soft-tissue changes were detected more frequently by MRI. This study suggests that MRI is likely to be of value for the early diagnosis of arthritis.