title: Magnetic resonance water proton relaxation in protein solutions and tissue: T(1rho) dispersion characterization.
abstract: BACKGROUND
  Image contrast in clinical MRI is often determined by differences in tissue water proton relaxation behavior. However, many aspects of water proton relaxation in complex biological media, such as protein solutions and tissue are not well understood, perhaps due to the limited empirical data.
  
  
  RESULTS
  Water proton T(1), T(2), and T(1rho) of protein solutions and tissue were measured systematically under multiple conditions. Crosslinking or aggregation of protein decreased T(2) and T(1rho), but did not change high-field T(1). T(1rho) dispersion profiles were similar for crosslinked protein solutions, myocardial tissue, and cartilage, and exhibited power law behavior with T(1rho)(0) values that closely approximated T(2). The T(1rho) dispersion of mobile protein solutions was flat above 5 kHz, but showed a steep curve below 5 kHz that was sensitive to changes in pH. The T(1rho) dispersion of crosslinked BSA and cartilage in DMSO solvent closely resembled that of water solvent above 5 kHz but showed decreased dispersion below 5 kHz.
  
  
  CONCLUSIONS
  Proton exchange is a minor pathway for tissue T(1) and T(1rho) relaxation above 5 kHz. Potential models for relaxation are discussed, however the same molecular mechanism appears to be responsible across 5 decades of frequencies from T(1rho) to T(1).
authors.affiliation: Duke Cardiovascular Magnetic Resonance Center, Duke University Medical Center, Durham, North Carolina, United States of America. Ennling@duke.edu
authors.forename: Enn-Ling
authors.initials: EL
authors.lastname: Chen
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Kim
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008962:Models, Theoretical; D011506:Proteins / Q000737:chemistry*; D011522:Protons; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D014867:Water / Q000737:chemistry*
chemical_list: D011506:Proteins; D011522:Protons; D014867:Water