Functional imaging in OA: role of imaging in the evaluation of tissue biomechanics

Abstract

Functional imaging refers broadly to the visualization of organ or tissue physiology using medical image modalities. In load-bearing tissues of the body, including articular cartilage lining the bony ends of joints, changes in strain, stress, and material properties occur in osteoarthritis (OA), providing an opportunity to probe tissue function through the progression of the disease. Here, biomechanical measures in cartilage and related joint tissues are discussed as key imaging biomarkers in the evaluation of OA. Emphasis will be placed on the a) potential of radiography, ultrasound, and magnetic resonance imaging to assess early tissue pathomechanics in OA, b) relative utility of kinematic, structural, morphological, and biomechanical measures as functional imaging biomarkers, and c) improved diagnostic specificity through the combination of multiple imaging biomarkers with unique contrasts, including elastography and quantitative assessments of tissue biochemistry. In comparison to other modalities, magnetic resonance imaging provides an extensive range of functional measures at the tissue level, with conventional and emerging techniques available to potentially to assess the spectrum of preclinical to advance OA.

Functional MR Imaging Mapping of Human Articular Cartilage Response to Loading

“…In an effort to identify and establish more refined parameters to assess cartilage degeneration beyond structure and composition, the purpose of our study was to determine if multiparametric MR imaging mapping can be used to quantify the response to loading of histologically intact human knee cartilage. More specifically, we aimed to assess the regional and zonal response to loading of cartilage by using a set of MR imaging parameters of proven diagnostic value (4,6), to correlate them to conventional histologic and biomechanical measures as the reference standards, and to subsequently define the response to loading of histologically intact human cartilage. Our hypotheses were that (a) loading-induced changes in cartilage would be reflected by characteristic regional and zonal changes in MR imaging parameters and (b) the cartilage response to loading would be closely related to histologic and biomechanical reference measures.…”

“…However, current clinical routine imaging modalities cannot be used to identify these early disease stages (4,5). Hence, recent imaging strategies have focused on quantification of tissue properties, particularly quantitative magnetic resonance (MR) imaging, to yield information beyond morphology and structure and to include quantitative measures of the extracellular matrix components water, collagens, and proteoglycans (PGs) (4,6).…”

Is T1ρ Mapping an Alternative to Delayed Gadolinium-enhanced MR Imaging of Cartilage in the Assessment of Sulphated Glycosaminoglycan Content in Human Osteoarthritic Knees? An in Vivo Validation Study

“…These disadvantages are mainly related to the administration of contrast material, which increases costs and is potentially harmful to patients with impaired renal function, and the long delay between contrast material administration and MR imaging. Because of these drawbacks, T1r mapping was suggested as a non-contrast-enhanced alternative to dGEMRIC for the measurement of sGAG content (3,4,6). In T1r mapping, the spin relaxation is quantified in the rotating frame by using a constant radiofrequency field referred to as a "spinlock" pulse to change relaxation rates of water associated with large macromolecules in cartilage such as sGAG (7,8).…”

Non-invasive T1ρ mapping of the human cartilage response to loading and unloading

“…Currently, the most relevant and clinically applicable techniques are T2, T1r and T2* mapping and dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) (reviewed in 4e6 ). Now, it is not clear whether qMRI alone is sufficiently sensitive and specific to detect early degenerative changes, especially in consideration of the substantial intra-and inter-individual variability 7,8 . As softening is considered an early sign of degeneration 9 , the comprehensive image-based assessment of the tissue's response to loading provides a promising surrogate parameter for its functionality.…”