title: Two-site exchange revisited: a new method for extracting exchange parameters in biological systems.
abstract: A new analysis is presented which links real volume fractions, relaxation rates, and intracompartmental exchange rates directly with apparent volume fractions and relaxation rates obtained from biexponential fits of transverse magnetization decay curves. The analysis differs from previous methods in that measurements from two paramagnetic doping levels are used to close the two-site exchange equations. Both the new method and one previously described by Herbst and Goldstein (HG) have been applied to paramagnetically doped whole-blood data sets. Significant differences in the calculated exchange parameters are found between the two methods. A small dependence of the intracellular relaxation rate on extracellular paramagnetic agent concentration, assumed nonexistent with the HG method, is inferred from the new analysis. The analysis was also applied to published data on perfused rat hearts, and we obtained a limited assessment of two-site exchange in this system.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: R V
authors.initials: RV
authors.lastname: Mulkern
authors.forename: A R
authors.initials: AR
authors.lastname: Bleier
authors.forename: I K
authors.initials: IK
authors.lastname: Adzamli
authors.forename: R G
authors.initials: RG
authors.lastname: Spencer
authors.forename: T
authors.initials: T
authors.lastname: Sandor
authors.forename: F A
authors.initials: FA
authors.lastname: Jolesz
mesh_terms: D001826:Body Fluids / Q000378:metabolism*; D002712:Chlorides; D004912:Erythrocytes / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism*; D019786:Gadolinium DTPA; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D008345:Manganese / Q000097:blood; D017895:Manganese Compounds; D008433:Mathematics; D008954:Models, Biological; D009942:Organometallic Compounds / Q000097:blood; D004369:Pentetic Acid / Q000097:blood
chemical_list: D002712:Chlorides; D017895:Manganese Compounds; D009942:Organometallic Compounds; D008345:Manganese; D004369:Pentetic Acid; D019786:Gadolinium DTPA; C025340:manganese chloride