Load-dependent low-field profiling and relaxometry of osteoarthritic articular cartilage

At low magnetic fields, T1 variation within cartilage represents a robust parameter that is employed to quantify the layered structure in the tissue and is sensitive to factors such as enzymatic degradation, external load, and diseases such as osteoarthritis. Variable-field relaxometry provides access to the quadrupolar dips that probe proton-nitrogen interaction and thus the content and local order of glycosaminoglycans and collagen. In this study on 20 human cartilage samples, low-field and variable-field techniques were combined for the first time to correlate NMR parameters and response to load with the severity of osteoarthritis. While low-field MRI significantly enhances the T1 contrast in cartilage tissue, variable-field relaxometry identifies the properties of cartilage and glycosaminoglycan (GAG) as well as overall molecular mobility. In particular, the N content of both collagen and GAG give rise to so-called quadrupolar dips, i.e. enhanced relaxation rates of H particularly at field strengths between 50 and 70 mT. In this study, both methods are combined for the first time with the purpose of quantifying correlations with the degree of osteoarthritic degeneration in human cartilage, and to establish cross-correlations between lowfield and variable-field NMR.