title: Proteoglycan depletion-induced changes in transverse relaxation maps of cartilage: comparison of T2 and T1rho.
abstract: OBJECTIVE
  The authors performed this study to (a) measure changes in T2 relaxation rates, signal-to-noise ratio (SNR), and contrast with sequential depletion of proteoglycan in cartilage; (b) determine whether there is a relationship between the T2 relaxation rate and proteoglycan in cartilage; and (c) compare the T2 mapping method with the spin-lattice relaxation time in the rotating frame (T1rho) mapping method in the quantification of proteoglycan-induced changes.
  
  
  METHODS
  T2- and T1rho-weighted magnetic resonance (MR) images were obtained in five bovine patellae. All images were obtained with a 4-T whole-body MR unit and a 10-cm-diameter transmit-receive quadrature birdcage coil tuned to 170 MHz. T2 and T1rho maps were computed.
  
  
  RESULTS
  The SNR and contrast on the T2-weighted images were, on average, about 43% lower than those on the corresponding T1rho-weighted images. The T2 relaxation rates varied randomly without any particular trend, which yielded a poor correlation with sequential depletion of proteoglycan (R2 = 0.008, P < .70). There was excellent linear correlation between the percentage of proteoglycan in the tissue and the T1rho relaxation rate (R2 = 0.85, P < .0001).
  
  
  CONCLUSIONS
  T2-weighted imaging neither yields quantitative information about the changes in proteoglycan distribution in cartilage nor can be used for longitudinal studies to quantify proteoglycan-induced changes. T1rho-weighted imaging, however, is sensitive to sequential depletion of proteoglycan in bovine cartilage and can be used to quantify proteoglycan-induced changes.
authors.affiliation: MMRRCC, Department of Radiology, B1, Stellar-Chance Laboratories, University of Pennsylvania Medical Center, 422 Curie Blvd, Philadelphia, PA 19104-6100, USA.
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: J Bruce
authors.initials: JB
authors.lastname: Kneeland
authors.forename: Ravinder
authors.initials: R
authors.lastname: Reddy
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000737:chemistry* / Q000000981:diagnostic imaging; D002417:Cattle; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods; D023421:Models, Animal; D009126:Muscle Relaxation / Q000502:physiology*; D010329:Patella / Q000737:chemistry / Q000000981:diagnostic imaging; D011509:Proteoglycans / Q000378:metabolism*; D011859:Radiography; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000502:physiology; D013223:Statistics as Topic; D013997:Time Factors
chemical_list: D011509:Proteoglycans