title: Proton spin-lock ratio imaging for quantitation of glycosaminoglycans in articular cartilage.
abstract: OBJECTIVE
  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(1rho)) imaging and T(1rho) relaxivity (R(1rho)).
  
  
  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(1rho) measurements were made using a fast spin echo (FSE) sequence pre-encoded with a three-pulse cluster consisting of two 90 degrees 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(1rho) ratio imaging method (71 +/- 4%) and GAG measured from spectrophotometric assay (75 +/- 5%) in intact bovine tissue.
  
  
  CONCLUSIONS
  We have demonstrated a proton spin-lock ratio imaging method to quantify absolute GAG distribution in the cartilage in a noninvasive and nondestructive manner.
authors.affiliation: MMRRCC, Department of Radiology, Stellar-Chance Laboratories, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-6100, USA. regatte@mail.mmrrcc.upenn.edu
authors.forename: Ravinder Reddy
authors.initials: RR
authors.lastname: Regatte
authors.forename: Sarma V S
authors.initials: SV
authors.lastname: Akella
authors.forename: Arijitt
authors.initials: A
authors.lastname: Borthakur
authors.forename: Ravinder
authors.initials: R
authors.lastname: Reddy
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D002417:Cattle; D006025:Glycosaminoglycans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging
chemical_list: D006025:Glycosaminoglycans