Proton spin‐lock ratio imaging for quantitation of glycosaminoglycans in articular cartilage

Purpose To quantify glycosaminoglycans (GAG) in intact bovine patellar cartilage using the proton spin‐lock ratio imaging method. This approach exploits spin‐lattice relaxation time in the rotating frame (T 1ρ ) imaging and T 1ρ relaxivity (R 1ρ ). Materials and Methods All the magnetic resonance imaging (MRI) experiments were performed on a 4‐T whole‐body GE Signa scanner (GEMS, Milwaukee, WI), and spectroscopy experiments of chondroitin sulfate (CS) phantoms were done on a 2‐T custom‐built spectrometer. A custom‐built 11‐cm‐diameter transmit‐receive birdcage coil, which was tuned to a proton frequency of 170 MHz, was employed for the imaging experiments. T 1ρ measurements were made using a fast spin echo (FSE) sequence pre‐encoded with a three‐pulse cluster consisting of two 90° hard pulses separated by a low‐power rectangle pulse for spin‐locking. Results The methodology is first validated on CS phantoms and then used to quantify GAG content in intact bovine cartilage ( N = 5). There is a good agreement between the GAG map calculated from the T 1ρ ratio imaging method (71 ± 4%) and GAG measured from spectrophotometric assay (75 ± 5%) in intact bovine tissue. Conclusion We have demonstrated a proton spin‐lock ratio imaging method to quantify absolute GAG distribution in the cartilage in a noninvasive and nondestructive manner. J. Magn. Reson. Imaging 2003;17:114–121. © 2002 Wiley‐Liss, Inc.