Pulsed-field gradient-nuclear magnetic resonance (PFG NMR) to measure the diffusion of ions and polymers in cartilage: applications in joint diseases.

Abstract

Since cartilage contains neither blood nor lymph vessels, diffusion is the most important transport process for the supply of cartilage with nutrients and for the removal of metabolic waste products. Therefore, diffusion measurements are of high interest in cartilage research. Different techniques of diffusion measurements exist. Here we describe methods based on pulsed-field gradient nuclear magnetic resonance (PFG NMR). This technique offers the considerable advantage that neither concentration gradients nor labeling of the diffusing species are required. In addition to the description of the fundamentals and the applicability of PFG NMR studies in cartilage research, emphasis is on the influence of the observation time, Delta, on the diffusion coefficient, D: at short times, diffusion is primarily determined by the water content of the sample, and great care is needed to keep this parameter constant. However, by varying the diffusion time, data on the internal structure of cartilage, e.g., the distance of the collagen fibrils, can also be obtained. In addition to classical water diffusion, the diffusion behavior of selected ions and polymers in cartilage is described. The capabilities, the limitations, and the clinical relevance of diffusion measurements for the assessment of joint diseases are discussed.