To assess the applicability of quantitative MR microscopy for the detection of glycosaminoglycan (GAG) depletion as an early sign of degeneration in the articular cartilage of humans treated by trypsin.

Four cartilage-bone blocks were obtained from the patient who had suffered from osteoarthritis of the knee and underwent a total knee replacement arthroscopy. Each articular cartilage segment was resected as to a round disk shape (8 mm in diameter) with a remnant of subchondral bone 1 mm in thickness. Four different culture solutions were prepared, and these solutions were 0.2 mg/ml of trypsin solution (group 1), 1 mM of Gd (DTPA) 2-mixed trypsin solution (group 2), phosphate buffered saline (PBS) (group 3), and 1 mM of Gd (DTPA) 2-mixed PBS (group 4). The cartilages were cultured and then MR imagings were performed every hour for 5 hrs, and we continued the additional cultures of 24 hrs, 36 hrs and 48 hrs. Three imaging sequences were used: T1-weighted spin echo (TR/TE, 450/22), proton density turbo spin echo with fat suppression (TR/TE, 3000/25), and CPMG (Carr-Purcell-Meiboom-Gill) (TR/TE/TI, 760/21-168, 360). MR imaging data were analyzed with pixel-by-pixel comparisons in all groups.

The GAG loss in the articular cartilage was increased proportionately to the culture duration. Mean changes of T1 relaxation time were 1.2% for group 1, -1.9% for group 3, -54.7% for group 2 and -64.2% for group 4 (p<0.05). When comparing by linear profile on the T1-weighted images, SNR increased and T1 relaxation time decreased for group 2 and 4, as the culture duration increased (p<0.05). On the correlation analysis, there is significant correlation between GAG loss and Gd (DTPA) 2-enhancement for group 2 (p=0.0431), but there was no significant difference for group 4 (p=0.0918). More enhancement with Gd (DTPA) 2-was noted for group 2 than for group 4. Group 2 showed a diffuse enhancement in all the layers of cartilage, but for group 4, prominent enhancement was noted only in the superficial layer.

Early degenerative changes of the articular cartilage were not noted on the T1-weighted images, turbo spin echo with fat suppresison and T1, T2, or the rho relaxometry by a 1.5 T machine. Only Gd (DTPA) 2- enhancement was useful in the detection of early degeneration of the articular cartilage.