Osteoarthritis is a degenerative disease of cartilage, affecting 40 million Americans and more than 80% of people age 55 and over. It is characterized by degradation of the cartilage matrix with symptoms of joint stiffness and swelling, bony enlargements, and pain. Cartilage consists mainly of an extra-cellular matrix (ECM) of type II collagen and proteoglycans, in an intertwining array. Water content in cartilage ranges from 70% to 80%. Approximately 60% of the dry weight of cartilage is collagen, with the remainder mostly being the proteoglycans (PG). It is now known that degradation of cartilage in an early osteoarthritic condition primarily involves the loss of the PG. We have imaged a healthy human knee using saline/agarose phantoms whose 23Na relaxation times have been normalized to cartilage. This allows the creation of a calibration curve to fit pixel intensities of the cartilage to in an effort to quantitate the signal. This sodium signal directly corresponds to the PG content in the cartilage, thereby providing a method to monitor tissue integrity. We are investigating the use of surface coils, a birdcage coil and a transmit only birdcage coil with surface receive coils. We are currently underway in a plan to determine sodium concentrations in several healthy human volunteers as well as subjects grouped by age.
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