Advanced techniques of magnetic resonance imaging in the diagnosis of articular cartilage lesions

Abstract

Articular cartilage is one of the most essential tissues for healthy joint function, cartilage has obvious and fundamental roles in joint function and body movement, it is a type of fine connective tissue composed of a complex mesh of collagenous fibers, water and proteoglycans. There are many diagnostic imaging methods for evaluation of the articular cartilage. Conventional radiography has been used to detect secondary gross changes of the joint cartilage, manifested by the narrowing of the joint space distance, and allows visualization of secondary changes, such as osteophyte formation, but this imaging method only allows detection of later stage of the disease when changes are already irreversible. It does not allow direct visualization of the cartilage. Conventional or computed tomography arthrography has also been used to evaluate surface irregularities of the cartilage; however, it is limited in its invasiveness and provides limited evaluation. MRI is the most accurate noninvasive method available to diagnose disorders of articular cartilage. Conventional MRI techniques have long been used to assess the quality of articular cartilage in patients with joint pain or pathology. Most current MRI techniques focus on cartilage morphology. MR imaging has become the best imaging modality for assessment of the articular cartilage because of its ability to manipulate contrast to highlight different tissue types. Conventional MR imaging sequences that are currently used for evaluation of cartilage have the ability to depict mostly morphologic changes, such as fibrillation and partial-thickness or full thickness defects; however, they are limited in their capability for comprehensive assessment of cartilage, with limited spatial resolution and limited information about cartilage physiology. Commonly used conventional MR imaging methods include two-dimensional or multi slice T1-weighted, proton density (PD)-weighted, and T2-weighted imaging with or without fat suppression New developments in imaging hardware and software include improved gradients and radiofrequency coils, fast or turbo spin echo imaging techniques such as water-only excitation. Although spoiled gradient recalled (SPGR) and gradient echo (GRE) techniques have produced excellent images with high resolution and three-dimensional (3D) SPGR is considered the current standard for morphologic imaging of cartilage, these methods have the disadvantages of lack of reliable contrast between cartilage and fluid and long imaging times. Therefore, newer techniques have emerged for morphologic imaging of cartilage, some of which include dual-echo steady-state (DESS) imaging, driven equilibrium Fourier transform (DEFT) imaging, balanced steady-state free precession (SSFP) imaging with fat suppression and its variants. Recent advances in biochemical imaging have allowed researchers to focus more on the biochemical composition of articular cartilage, Detection of the biochemical abnormalities in cartilage that precede morphologic changes will lead to a better understanding of early cartilage injury New biochemical imaging techniques, such as T2 mapping, T1rho (spin‐lattice relaxation in the rotating frame) imaging, sodium MRI, and delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC), have been used to directly assess articular cartilage, with the presumption that early detection and management of articular cartilage lesions may assist in preventing the progression of degenerative arthritis.

These techniques are promising in relation to their clinical application in the near future, especially in relation to early detection of chondral lesions before their manifestation as macroscopic anatomical lesions.T2 mapping assesses the water content and ultrastructure of the tissue collagen. The T2 relaxation time measurement demonstrates areas of greater or smaller water content, depending on the chondral lesion. This measurement is represented by a map on a scale of colors. Longer T2 relaxation time in focal areas of cartilage is associated with damage to the chondral matrix and, especially, loss of collagen integrity. In T1-rho mapping There is a promising technique that is very sensitive for evaluating early depletion of proteoglycans. In d-GMERIC (delayedgadolinium-enhanced MRI of cartilage) Proteoglycan consists of glycosaminoglycan chains with abundant positive charges. The paramagnetic contrast most used is gadolinium (Gd-DTPA), and this also presents negative charges. After intravenous injection, the paramagnetic contrast penetrates the cartilage and is distributed to areas with low glycosaminoglycan concentration Through a T1 map, the Gd-DTPA concentration can be quantified and, consequently, the glycosaminoglycan content.