Water distribution patterns inside bovine articular cartilage as visualized by H-1 magnetic resonance imaging

Objective: To develop a magnetic resonance imaging (MRI) technique to non-i nvasively map water volume fraction (WVF) in articular cartilage. Special e mphasis was placed on spatial resolution and temporal considerations, aimed at creating a procedure feasible for eventual human studies. Design: Absolute proton density MR images of intact, ex vivo bovine patella e were calculated from fully T-1 relaxed, short echo time images. This was accomplished through compensation for T-2 decay with calculated T-2 maps. C alibration of the signal intensity in the image was accomplished with the u se of H2O:D2O phantoms, where the WVF was varied from 0.95 to 0.75. Applica tion of the calibration curve to the entire image yielded images that repre sent WVF on a pixel by pixel basis. Calculations of water content by weight were performed by considering the density of the solid content. Results: Using four echo time points, experiments comparing MR images from single-echo and multi-echo spin echo sequences yielded similar results. T-2 decreased with depth through the cartilage, with a maximum at the articula r surface of approx 100 ms, and a -50 ms minimum at the bone/cartilage inte rface, The WVF through the depth of the cartilage showed a similar trend, d ecreasing from 0.9 at the surface, to 0.7 at the bone/cartilage interface. Translation to a weight percent yielded similar to 86% weight at the surfac e, trending down to -63% at the bone/cartilage interface, with an average o f 74.5% for five patellae. These MRI derived values were compared to the me asured weight of water in excised cartilage plugs from the same patellae an d showed remarkably close agreement. Conclusion: We have demonstrated that MRI can non-invasively map WVF in car tilage in a pixel by pixel manner. This was accomplished in a time span tha t was clinically feasible, allowing the routine use of this method in a cli nical setting. Moreover, this procedure employed standard MRI equipment and pulse sequences, avoiding the need for hardware modifications and using si mple post processing methods. However, baseline studies need to be performe d prior to incorporation into a standard radiological evaluation. Implicati ons in the diagnosis of osteoarthritis (OA) are discussed. (C) 2001 OsteoAr thritis Research Society International.