Nine asymptomatic subjects and six patients underwent T 1 q MRI to determine whether Outerbridge grade 1 or 2 cartilage degeneration observed during arthroscopy could be detected noninvasively. MRI was performed 2-3 months postarthroscopy, using sagittal T 1 -weighted and axial and coronal T 1 q MRI, from which spatial T 1 q relaxation maps were calculated from segmented T 1 -weighted images. Median T 1 q relaxation times of patients with arthroscopically documented cartilage degeneration and asymptomatic subjects were significantly different (P < 0.001), and median T 1 q exceeded asymptomatic articular cartilage median T 1 q by 2.5 to 9.2 ms. In eight observations of mild cartilage degeneration at arthroscopy (Outerbridge grades 1 and 2), mean compartment T 1 q was elevated in five, but in all observations, large foci of increased T 1 q were observed. It was determined that T 1 q could detect some, but not all, Outerbridge grade 1 and 2 cartilage degeneration but that a larger patient population is needed to determine the sensitivity to these changes. The need to noninvasively detect the earliest changes in the degeneration of articular cartilage in order to both use and validate disease modifying osteoarthritic drugs has stimulated considerable interest in the development of techniques that can directly probe the macromolecular structure. Three MRI techniques that were developed to directly assess the loss of proteoglycan that occurs during the early phases of osteoarthritis are sodium imaging, delayed gadolinium-enhanced MRI of cartilage and T 1 qweighted MRI. T 2 mapping is also widely used to assess the macromolecular constitution of cartilage (1-4), but collagen concentration and orientation alter the relaxation rate; thereby, it is not a specific measure of proteoglycan. On the other hand, changes in collagen orientation may be among the first changes to occur and have been visualized by T 2 mapping (5).Only a limited amount of research, however, has been performed to investigate the accuracy of the techniques used to probe proteoglycan content with the use of arthroscopy as the gold standard. In 15 patients with arthroscopically confirmed early changes of osteoarthritis, who were studied with the delayed gadoliniumenhanced MRI of cartilage technique, T 1 was lower in the compartment with those changes than in a reference compartment, indicating the loss of proteoglycan (6). In a similar study employing the delayed gadoliniumenhanced MRI of cartilage technique, a decrease in T 1 was observed to correlate with abnormal arthroscopic findings, and average T 1 relaxation times were significantly different between radiographic grade 0 and grade 1 changes (7). No research currently exists to correlate sodium concentration to arthroscopy. All three techniques are limited in some respects: delayed gadoliniumenhanced MRI of cartilage requires the administration of exogenous contrast agents; sodium MRI requires specialized hardware and has relatively lower concentration than protons, short relaxation times, and low...
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