Abstract
Anisotropy of transverse proton spin relaxation in collagen-rich tissues like cartilage and tendon is a well-known phenomenon that manifests itself as the “magic-angle” effect in magnetic resonance images of these tissues. It is usually attributed to the non-zero averaging of intra-molecular dipolar interactions in water molecules bound to oriented collagen fibers. One way to manipulate the contributions of these interactions to spin relaxation is by partially replacing the water in the cartilage sample with deuterium oxide. It is known that dipolar interactions in deuterated solutions are weaker, resulting in a decrease in proton relaxation rates. In this work, we investigate the effects of deuteration on the longitudinal and the isotropic and anisotropic contributions to transverse relaxation of water protons in bovine articular cartilage. We demonstrate that the anisotropy of transverse proton spin relaxation in articular cartilage is independent of the degree of deuteration, bringing into question some of the assumptions currently held over the origins of relaxation anisotropy in oriented tissues.
Highlights
Spin relaxation of water protons is a useful marker of the microstructure and composition of biological tissues [1, 2], including articular cartilage [3,4,5]
These interactions are mediated by the dynamics of the water molecules, which in turn depend on the biopolymeric composition and cellular organisation of the tissue
We present the results from our study of proton spin relaxation behaviour in bovine articular cartilage in the presence of deuterium oxide
Summary
Spin relaxation of water protons is a useful marker of the microstructure and composition of biological tissues [1, 2], including articular cartilage [3,4,5]. Proton spin relaxation is determined by intra- and intermolecular interactions of spins with the magnetic moments of neighbouring nuclei. These interactions are mediated by the dynamics of the water molecules, which in turn depend on the biopolymeric composition and cellular organisation of the tissue. Anisotropy of Spin Relaxation in Articular Cartilage the orientation of the tissue relative to the applied magnetic field (B0). This dependence (the so-called relaxation anisotropy) can be used as a probe of the three-dimensional architecture of the tissue at the microscopic level and can inform the interpretation of Magnetic Resonance Imaging (MRI) studies of cartilage biomechanics [6,7,8], complementing other MRI [9,10,11] and non-MRI [12] techniques
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