title: Efficiency of paramagnetic relaxation enhancement in off-resonance rotating frame.
abstract: Transferring from laboratory frame to off-resonance rotating frame for the (1)H spin can compensate the relaxivity loss for paramagnetic agents at the magnetic field strength higher than 3 Tesla and enhance water relaxation rate constant significantly. A comprehensive theory for calculating the relaxation rate constants in the off-resonance rotating frame is described. This theory considers the contributions from both inner shell and outer shell water. The derived relaxation rate constants and relaxation enhancement efficiency as a function of the magnetic field strength and the effective field parameters are directly correlated to the structures, dynamics and environments of paramagnetic agents. To validate the theoretical predictions, we have measured the relaxation enhancement efficiency for a series of macromolecule conjugated gadolinium chelates at 9.4 Tesla. The experimental results confirmed the theoretical predictions. The theory also predicts the relaxation enhancement for T(2)-type paramagnetic agents at high magnetic fields. Promising fields of applications include situations where T(1)- or T(2)-type paramagnetic agents are used for labeling molecular/cellular events.
authors.affiliation: Center for Basic MR Research, Evanston Northwestern Healthcare Research Institute, Evanston, IL 60201, USA. h-zhang1@northwestern.edu
authors.forename: Huiming
authors.initials: H
authors.lastname: Zhang
authors.forename: Yang
authors.initials: Y
authors.lastname: Xie
mesh_terms: D000818:Animals; D002417:Cattle; D003287:Contrast Media / Q000737:chemistry*; D050091:Dendrimers; D003911:Dextrans / Q000737:chemistry; D019786:Gadolinium DTPA / Q000737:chemistry*; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008962:Models, Theoretical; D011073:Polyamines / Q000737:chemistry; D011107:Polylysine / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry
chemical_list: D003287:Contrast Media; D050091:Dendrimers; D003911:Dextrans; D046911:Macromolecular Substances; C104700:PAMAM Starburst; D011073:Polyamines; D012709:Serum Albumin; D011107:Polylysine; D019786:Gadolinium DTPA