Techniques and applications of in vivo diffusion imaging of articular cartilage

Abstract

Early in the process of osteoarthritis (OA) the composition (water, proteoglycan [PG], and collagen) and structure of articular cartilage is altered leading to changes in its mechanical properties. A technique that can assess the composition and structure of the cartilage in vivo can provide insight in the mechanical integrity of articular cartilage and become a powerful tool for the early diagnosis of OA. Diffusion tensor imaging (DTI) has been proposed as a biomarker for cartilage composition and structure. DTI is sensitive to the PG content through the mean diffusivity (MD) and to the collagen architecture through the fractional anisotropy (FA). However, the acquisition of DTI of articular cartilage in vivo is challenging due to the short T2 of articular cartilage (~40 ms at 3 T) and the high resolution needed (0.5-0.7 mm in plane) to depict the cartilage anatomy. We describe the pulse sequences used for in vivo DTI of articular cartilage and discus general strategies for protocol optimization. We provide a comprehensive review of measurements of DTI of articular cartilage from ex vivo validation experiments to its recent clinical applications.

Diffusion tensor imaging of the anterior cruciate ligament graft

“…DTI of ligament and tendon is technically challenging because of the small size and short T 2 relaxation times of these tissues . Additionally, the knee joint has a complex anatomy that causes changes in the magnetic field (B 0 ) that can lead to susceptibility artifacts, especially at the intercondylar notch and ACL insertion sites . We performed DTI of the ACL graft using new state‐of‐the‐art 3T technology equipped with powerful gradients (maximum amplitude = 80 mT/m; slew rate 200 T/m/s) permitting DWIs to be acquired at a shorter TE (45 msec), which improves SNR and reduces susceptibility artifacts .…”

“…The vast majority of DTI studies have investigated the brain, peripheral nerves, and muscles . More recently, DTI of articular cartilage has been described …”

Diffusion tensor imaging of articular cartilage at 3T correlates with histology and biomechanics in a mechanical injury model

“…The design of this experiment differs from earlier work. Previous models of cartilage damage, which have been used for the validation of MRI parameters, use enzymatic degradation (mostly with trypsin) that degrades the cartilage matrix in an artificial way that does not corresponds with the early degenerative changes leading to PTOA.…”

Stabilization of T2 relaxation and magnetization transfer in cartilage explants by immersion in perfluorocarbon liquid

“…A standard ex vivo paradigm is to measure T 2 and MTR following pathomimetic degradation, in which cartilage is exposed to an aqueous enzyme solution . The extent of T 2 increase and MTR decrease is taken as a measure of degradation.…”