title: Sensitivity of USPIO-enhanced R2 imaging to dynamic blood volume changes in the rat kidney.
abstract: OBJECTIVE
  To determine whether MRI in combination with an intravascular contrast agent is sensitive to pharmacologically induced vasodilation and vasoconstriction in the rat kidney.
  
  
  METHODS
  R(2) imaging was performed in 25 Sprague Dawley rats at 3 Tesla in the presence of ferumoxytol, an ultrasmall superparamagnetic iron oxide (USPIO) agent with a long plasma half-life. R(2) changes were measured following manipulation of blood volume by intravenous administration of adenosine, a short-acting vasodilator, or N(G)-nitro-L-arginine methyl ester (L-NAME), a long-acting nitric oxide synthase inhibitor with known vasoconstrictive effects. As a control, R(2) responses to adenosine and L-NAME were also examined in the absence of ferumoxytol.
  
  
  RESULTS
  In the presence of ferumoxytol, adenosine induced a significant increase in R(2), while L-NAME produced a reduction, although the latter was not statistically significant. Control experiments revealed small R(2) changes in the absence of ferumoxytol. An incidental finding was that the cross-sectional area of the kidney also varied dynamically with adenosine and L-NAME.
  
  
  CONCLUSIONS
  Our results suggest that ferumoxytol-enhanced R(2) imaging is sensitive to adenosine-induced vasodilation. The responses to L-NAME, however, were not statistically significant. The variations in kidney size and the R(2) changes in the absence of ferumoxytol may reflect alterations in the volume of the renal tubules.
authors.affiliation: Radiology Department, Evanston Hospital, Evanston, Illinois, USA. pippa.storey@nyumc.org
authors.forename: Pippa
authors.initials: P
authors.lastname: Storey
authors.forename: Lin
authors.initials: L
authors.lastname: Ji
authors.forename: Lu-Ping
authors.initials: LP
authors.lastname: Li
authors.forename: Pottumarthi V
authors.initials: PV
authors.lastname: Prasad
mesh_terms: D000241:Adenosine / Q000737:chemistry; D000818:Animals; D003287:Contrast Media / Q000494:pharmacology; D003911:Dextrans / Q000494:pharmacology*; D052203:Ferrosoferric Oxide; D007668:Kidney / Q000187:drug effects / Q000473:pathology*; D007684:Kidney Tubules / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D058185:Magnetite Nanoparticles / Q000737:chemistry; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; C097921:ferumoxtran-10; D000241:Adenosine; D019331:NG-Nitroarginine Methyl Ester; D052203:Ferrosoferric Oxide