Assessment of collagen integrity in articular cartilage by using magnetization transfer imaging: In vivo application to the goat knee

measured in type I collagen samples at similar concentrations. This may be due to structural differences between the two types of collagen or bias in the phantom preparation that affected levels of hydration. The magnetization rate as well varied with the type I collagen concentration (y=0.58x0.43, r2=0.98). For a 50% decrease in type I collagen content (ie. from 10 to 5% w/v), a ~35% drop (1.59 to 1.05 s1) in the apparent k could be detected. When applied to bovine cartilage plugs, trypsin treatment did not result in obvious changes of MTR (trypsin: 0.33±0.04 vs. control: 0.36±0.03, NS). However, a ~50% drop in the MT effect was measured in articular cartilage when treated with Bac CLN (MTR=0.14±0.04, vs. control p<0.05). The MTR for bovine nasal cartilage was consistently lower (20 to 30%) as compared with articular cartilage. None of the enzymatic treatments changed MTR in the thicker nasal cartilage disks during 24h incubation. These data are in good agreement with biochemical assessments of collagen in articular cartilage. Of interest to note, both trypsin and Bac CLN treatments resulted in significant PG depletion. Fig. 1 shows a typical MTR image series obtained with various MT pulse lengths and used to calculate the in vivo rate constant k. In average, ~40% signal attenuation (MTR=0.35±0.01, n=3) was measured in articular cartilage of the normal knee. The corresponding magnetization rate was k=3.18±0.25 s-1. These values remained unchanged when the knee was injected with 30 papain units (MTR=0.34±0.02, k=3.09±0.08 s-1, n=3). However a slight decrease was observed in goats that received 100 units (MTR=0.31±0.02, n=2; k=2.60 s-1, n=1), an effect that became even more pronounced in goats pre-injected with 390 units (MTR=0.22±0.01, n=2). Interestingly, additional measurements based on Gd(DTPA)2--enhanced MRI (4) have shown significant papain-induced PG depletion in the articular cartilage of these goats even when only 30 papain units were injected.