Activation Energy Mapping in Articular Cartilage

Abstract

Magnetic resonance imaging of articular cartilage has, in the past, had a primary focus on clinical, qualitative imaging or quantitative mapping purely using relaxation times (e.g. T1 and T2) and the development of phenomenological models to link these to physical properties, such as GAG content. Recent work in the field has looked at more advanced imaging methods, such as dGEMRIC, gagCEST and diffusion tensor imaging in order to attempt to develop a more direct link to physical and biochemical properties of the cartilage. This link is important to further understand the structure and function of cartilage, and here we investigate a novel method to probe the physical and biochemical properties of cartilage tissue. We present a novel method for visualising cartilage using magnetic resonance imaging techniques, which have been developed for probing the structure, mobility and hydration of soft-matter systems. This approach has been used to determine the dynamic activation energy (EA) of water within articular cartilage. Two related imaging methods have been explored: firstly quantitative mapping of the T1-relaxation time over a range of temperatures and secondly, quantitative mapping of the apparent diffusion coefficient over a range of temperatures. These are complementary techniques that probe the local tissue environment by extracting the rotational activation energy of the water within articular cartilage from the T1-relaxation time mapping, and the translational activation energy from the apparent diffusion coefficient mapping. These methods have been shown to provide different information from within the articular cartilage tissue to that seen with other imaging techniques. These quantitative maps can provide a link to biochemical contents or physical properties of articular cartilage tissue and can be interpreted in terms of the known structure and properties of cartilage from other methods