Magnetic resonance imaging of osteoarthritis.

Considering the plethora of imaging protocols, joint-specific orientations, and potential artifacts, the design and interpretation of MR imaging examination is difficult. Like a physical examination, these considerations must be tailored to the specific tissue, joint, and clinical question under consideration. Shortcomings of MR imaging include the lack of consensus among radiologists with respect to which protocols best image articular joints. To date, few prospective studies have been undertaken to assess osteoarthritis by MR imaging. Diagnostic imaging is central to staging the severity of osteoarthritis and assessing the efficacy of therapeutic osteoarthritis. Plain film radiography is insensitive for identifying early changes of osteoarthritis. Tailored MR imaging, producing high spatial and or contrast resolution images, is proving to be an important tool in the early detection and surveillance of osteoarthritis progression. Future therapeutic techniques, such as chondrocyte transplantation, use of growth factors, or cartilage protease inhibitors requires high resolution and volumetric MR imaging studies for accurate identification of focal articular cartilage defects and generalized cartilage loss. Creation of cartilage models by three-dimensional MR image rendering may be helpful for preoperative planning of orthopedic surgical procedures in advanced cases of osteoarthritis. More work needs to be done in high resolution and volumetric MR imaging of articular cartilage. Given the availability of new disease-modifying treatments designed to prevent, delay the progression of, or reverse osteoarthritis, additional prospective MR imaging studies need to be undertaken to improve the reproducibility of MR imaging as a primary outcome measure in the evaluation of osteoarthritis. Interinstitutional standardization of specific MR imaging magnet strengths, surface coils, joint orientations, sequences used, scoring systems and quality assurance methodologies are needed to establish the reproducibility of MR imaging and interpretation for assessment of patients with osteoarthritis.

In vitro and in vivo MR imaging of hyaline cartilage: zonal anatomy, imaging pitfalls, and pathologic conditions.

Hyaline cartilage plays an essential role in the maintenance of normal synovial joint function by reducing friction and distributing loads. Histologic analysis of hyaline cartilage reveals zonal variation in cellular morphology, proteoglycan concentration, and collagen fiber size and orientation. High-resolution magnetic resonance (MR) imaging reveals an analogous laminar anatomy that is often visible on clinical images obtained with proper attention to technique. In vitro and in vivo pulse sequences show three distinct laminae: a hypointense superficial lamina, a hyperintense intermediate lamina, and a heterogeneous deep lamina that consists of alternating hyperintense and hypointense bands perpendicular to the subchondral bone. Imaging pitfalls include magic angle effects, truncation artifact, partial volume effect, regional anatomic variation, chemical shift, and magnetic susceptibility effects. Pathologic conditions that affect articular cartilage include chondromalacia patellae, osteoarthritis, and localized traumatic lesions. Although detection of early cartilage disease remains elusive, MR imaging can demonstrate intermediate and advanced lesions.

Hyaline cartilage: truncation artifact as a cause of trilaminar appearance with fat-suppressed three-dimensional spoiled gradient-recalled sequences.

PURPOSE: To investigate the cause of the trilaminar appearance within hyaline cartilage observed on magnetic resonance (MR) images obtained with a fat-suppressed three-dimensional spoiled gradient-recalled sequence. MATERIALS AND METHODS: The knees of three asymptomatic volunteers were imaged with a fat-suppressed, three-dimensional, spoiled gradient-recalled sequence. The field of view, number of phase-encoding steps, and phase-encoding direction were varied. On each image, the thickness of the patellar and trochlear cartilage was measured in millimeters and divided by the pixel dimension, which effectively expressed the thickness as the number of pixels. Finally, the number of pixels was compared with the number of alternating hyperintense and hypointense lines depicted. RESULTS: The number of truncation lines increased as pixel dimension was reduced by either decreasing the field of view or increasing the number of phase-encoding steps. The accuracy for predicting more than three lines with use of an anteroposterior phase-encoding direction varied between 83% and 92%. The appearance of the cartilage was altered when phase- and frequency-encoding directions were exchanged, but truncation lines were still evident. CONCLUSION: The trilaminar appearance depicted within hyaline cartilage on MR images obtained with this sequence is predominantly attributable to truncation artifact rather than to histologic zonal anatomy.