Effect of paramagnetic manganese cations on (1)H MRS of the brain.
Manganese cations (Mn(2+)) can be used as an intracellular contrast agent for structural, functional and neural pathway imaging applications. However, at high concentrations, Mn(2+) is neurotoxic and may influence the concentration of (1)H MR-detectable metabolites. Furthermore, the paramagnetic Mn(2+) cations may also influence the relaxation of the metabolites under investigation. Consequently, the purpose of this study was to investigate the effect of paramagnetic Mn(2+) cations on (1)H-MR spectra of the brain using in vivo and phantom models at 4.7 T. To investigate the direct paramagnetic effects of Mn(2+) cations on the relaxation of N-acetylaspartate (NAA), creatine and choline, T(1) relaxation times of metabolite solutions, with and without 5% albumin, and containing different Mn(2+) concentrations were determined. Relaxivity values with/without 5% albumin for NAA (4.8/28.1 s(-1) mM(-1)), creatine (2.8/2.8 s(-1) mM(-1)) and choline (1.8/1.1 s(-1) mM(-1)) showed NAA to be the most sensitive metabolite to the relaxation effects of the cations. Using an in vivo optic tract tracing imaging model, we obtained two adjacent regions of interest in the superior colliculi with different water T(1) values (Mn(2+)-enhanced = 1.01 s; unenhanced = 1.14 s) 24 h after intravitreal injection of 3 microL 50 mM MnCl(2). Using phantom and in vivo water relaxation time data, we estimated the in vivo Mn(2+) concentration to be 2-8 microM. The phantom data suggest that limited metabolite relaxation effects would be expected at this concentration. Consequently, this study indicates that, in this model, the presence of Mn(2+) cations does not significantly affect (1)H-MR spectra despite possible toxic and paramagnetic effects.
Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Denmark. kathrine@drcmr.dk
Kathrine Skak
KS
Madsen
David Alberg
DA
Holm
Lise Vejby
LV
Søgaard
Ian J
IJ
Rowland
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D001921:Brain / Q000187:drug effects* / Q000378:metabolism*; D002412:Cations / Q000494:pharmacology; D002794:Choline / Q000032:analysis*; D003401:Creatine / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008345:Manganese / Q000008:administration & dosage*; D011522:Protons; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D002412:Cations; D011522:Protons; D001224:Aspartic Acid; D008345:Manganese; C000179:N-acetylaspartate; D003401:Creatine; D002794:Choline