Proteoglycan (PG) depletion-induced changes in T 1 (spin-lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin-lock cluster pre-encoded fast spin echo sequence, T 1 maps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin-lock frequencies.

One of the initiating steps of osteoarthritis is the loss of proteoglycan (PG) molecules from the cartilage matrix. One method for assessing cartilage integrity, therefore, is to measure the PG content or fixed charge density (FCD) of cartilage. This report shows the feasibility of calculating FCD by 23 Na MRI and introduces MRI protocols for human studies, in vivo.23 Na MRI was used to measure the sodium concentration inside bovine patellar cartilage. The sodium concentration was then converted to FCD (mM) by considering ideal Donnan equilibrium. These FCD measurements were compared to FCD measurements obtained through standard dimethylmethylene blue PG assays. There was a high correlation (slope ‫؍‬ 0.89, r 2 ‫؍‬ 0.81) between the FCD measurements obtained by 23 Na MRI and those obtained by the PG assays. These methods were then employed in quantifying the FCD of articular cartilage of human volunteers in vivo. Two imaging protocols were compared: one using a birdcage coil, the other using a transmit/receive surface coil. Both methodologies gave similar results, with the average sodium concentration of normal human patellar cartilage ranging from ϳ ϳ240 to 260 mM. This corresponds to

Purpose:To establish the specificity of T 1 with respect to fixed charge density (FCD) as a measure of proteoglycan (PG) content in cartilage during the onset of osteoarthritis (OA). Materials and Methods:T 1 -weighted and sodium MRI were performed on cartilage samples of enzymatically degraded bovine explants and natural osteoarthritic human samples representing controlled and physiological models of OA, respectively. Spatial maps of T 1 and FCD (measured using the previously validated method of sodium MRI) were calculated from image data. Data were extracted from the maps and subjected to linear regression to compare changes in T 1 with changes in FCD in each model. Tissue samples were subjected to histological staining for a reduction in PG content.Results: Plots of normalized T 1 rate vs. FCD were found to be strongly correlated (R 2 Ͼ 0.75 and 0.85) in both models with nearly the same slope of Ϸ1/2 (P Ͼ 0.51). Loss of PG in bovine and human tissue was confirmed by histology. Conclusion:The strong correlation of the FCD and T 1 data in both the controlled and physiological models demonstrates that changes in T 1 are due predominantly to changes in PG content. This work is a first step in establishing T 1 as a method of quantifying PG changes in early-stage OA. THE PATHOLOGY OF THE disease osteoarthritis (OA) results in significant changes to the biochemical composition of cartilage. Loss of proteoglycan content (PG) from the extracellular matrix (ECM) is characteristic of the early development of OA (1-3). Although changes in collagen content and structure have been discerned, during the beginning stages of the disease the collagenous component of the ECM is often preserved (3-5). A noninvasive technique to detect biochemical changes that precede morphological degeneration in tissue will have a substantial impact on early diagnosis and the evaluation of therapeutic efficacy of treatment.The sodium MRI method has previously been established as an accurate measure of fixed charge density (FCD), as validated by spectrophotometric assay (6). The direct relationship between FCD and PG allows FCD data obtained via sodium MRI to be used as a spatially resolved measure of PG. Since the FCD measurement is affected only by charged species, sodium MRI provides a highly specific measure of PG and can be used as a gold standard for validating other methods of PG quantification.A promising alternative to sodium MRI to detect PG changes in vivo is T 1 -weighted MRI (7). T 1 , the spinlattice relaxation in the rotating frame, is sensitive to low frequency interactions between water molecules and their local macromolecular environment, such as the PG constituent of the ECM in cartilage. T 1 -weighting can be incorporated into an MR imaging sequence by "T 1 -preparing" the magnetization using a long duration spin-lock pulse. The amplitude of the spin-lock pulse is commonly referenced in terms of its nutation frequency (␥B 1 ), which is on the order of a few kilohertz. T 1 is sensitive to molecular interaction processes having...

The OMENS system represents the most comprehensive, versatile, objective, and easily adaptable attempt at clinical classification of hemifacial microsomia to date. The authors propose a concise clinical evaluation form using a modified version of the system to promote the use of the OMENS system, to aid in the evaluation of hemifacial microsomia patients, and to assist in data sharing among academic institutions.