title: Human whole-blood (1)H2O longitudinal relaxation with normal and high-relaxivity contrast reagents: influence of trans-cell-membrane water exchange.
abstract: OBJECTIVE
  Accurate characterization of contrast reagent (CR) longitudinal relaxivity in whole blood is required to predict arterial signal intensity in contrast-enhanced MR angiography (CE-MRA). This study measured the longitudinal relaxation rate constants (R1 ) over a concentration range for non-protein-binding and protein-binding CRs in ex vivo whole blood and plasma at 1.5 and 3.0 Tesla (T) under physiologic arterial conditions.
  
  
  METHODS
  Relaxivities of gadoteridol, gadobutrol, gadobenate, and gadofosveset were measured for [CR] from 0 to 18 mM [mmol(CR)/L(blood)]: the latter being the upper limit of what may be expected in CE-MRA.
  
  
  RESULTS
  In plasma, the (1) H2 O R1 [CR]-dependence was nonlinear for gadobenate and gadofosveset secondary to CR interactions with the serum macromolecule albumin, and was well described by an analytical expression for effective 1:1 binding stoichiometry. In whole blood, the (1) H2 O R1 [CR]-dependence was markedly non-linear for all CRs, and was well-predicted by an expression for equilibrium exchange of water molecules between plasma and intracellular spaces using a priori parameter values only.
  
  
  CONCLUSIONS
  In whole blood, (1) H2 O R1 exhibits a nonlinear relationship with [CR] over 0 to 18 mM CR. The nonlinearity is well described by exchange of water between erythrocyte and plasma compartments, and is particularly evident for high relaxivity CRs.
authors.affiliation: Radiology, University of Washington, Seattle, Washington, USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Wilson
authors.forename: Mark
authors.initials: M
authors.lastname: Woods
authors.forename: Charles S
authors.initials: CS
authors.lastname: Springer
authors.forename: Sarah
authors.initials: S
authors.lastname: Bastawrous
authors.forename: Puneet
authors.initials: P
authors.lastname: Bhargava
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Maki
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods*; D001798:Blood Proteins / Q000737:chemistry* / Q000528:radiation effects; D002462:Cell Membrane / Q000737:chemistry*; D003287:Contrast Media / Q000737:chemistry* / Q000528:radiation effects; D017097:Electric Impedance; D005682:Gadolinium / Q000737:chemistry* / Q000528:radiation effects; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011522:Protons; D011829:Radiation Dosage; D014867:Water / Q000737:chemistry*
chemical_list: D001798:Blood Proteins; D003287:Contrast Media; D011522:Protons; D014867:Water; D005682:Gadolinium
keywords: MR angiography; MRI; contrast agents; relaxation rate constant; relaxation time constant