title: Effects of intracellular pH, blood, and tissue oxygen tension on T1rho relaxation in rat brain.
abstract: The effects of intracellular pH (pH(i)), paramagnetic macroscopic, and microscopic susceptibility on T(1) in the rotating frame (T(1rho)) were studied in rat brain. Intracellular acidosis was induced by hypercapnia and pH(i), T(1rho), T(2), diffusion, and cerebral blood volume (CBV) were quantified. Taking into account the CBV contribution, a prolongation of parenchymal T(1rho) by 4.5% was ascribed to a change in tissue water relaxation caused by a one unit drop in pH(i). Blood T(1rho) was found to prolong linearly with blood oxygenation saturation (Y). The macroscopic susceptibility contribution to parenchymal T(1rho) was assessed both through BOLD and an iron oxide contrast agent, AMI-227. The T(1rho) data from these experiments could be described by intravascular effects with insignificant effects of susceptibility gradients on tissue water. Tissue oxygen tension (PtO(2)) was manipulated and monitored with microelectrodes to assess its plausible contribution to microscopic susceptibility and relaxation. Parenchymal T(1rho) was virtually unaffected by variations in the PtO(2), but T(1) was shortened in hyperoxia and T(2) showed a negative BOLD effect in hypoxia. It is demonstrated that pH(i) directly modulates tissue T(1rho), possibly through its effect on proton exchange; however, neither BOLD nor PtO(2) directly influence tissue T(1rho). The observations are discussed in the light of physicochemical mechanisms contributing to the ischemic T(1rho) changes.
authors.affiliation: Department of Biomedical NMR and National Bio-NMR Facility, A.I.Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland.
authors.forename: Mikko I
authors.initials: MI
authors.lastname: Kettunen
authors.forename: Olli H J
authors.initials: OH
authors.lastname: Gröhn
authors.forename: M Johanna
authors.initials: MJ
authors.lastname: Silvennoinen
authors.forename: Markku
authors.initials: M
authors.lastname: Penttonen
authors.forename: Risto A
authors.initials: RA
authors.lastname: Kauppinen
mesh_terms: D000818:Animals; D001810:Blood Volume; D002545:Brain Ischemia / Q000097:blood / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D003287:Contrast Media; D003911:Dextrans; D052203:Ferrosoferric Oxide; D006863:Hydrogen-Ion Concentration; D007501:Iron; D008279:Magnetic Resonance Imaging; D058185:Magnetite Nanoparticles; D008297:Male; D010087:Oxides; D010100:Oxygen / Q000097:blood*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003287:Contrast Media; D003911:Dextrans; D058185:Magnetite Nanoparticles; D010087:Oxides; C097921:ferumoxtran-10; D007501:Iron; D010100:Oxygen; D052203:Ferrosoferric Oxide