Nitric oxide-haemoglobin interaction: a new biochemical hypothesis for signal changes in fMRI.
A new hypothesis on the origin of activation-induced signal changes in functional magnetic resonance imaging (fMRI) is presented, involving transient formation of paramagnetic species, i.e. methaemoglobin (Hb+) and nitrosylhaemoglobin (Hb-NO), by reaction of nitric oxide (NO) with oxy-(Hb-O2) and deoxyhaemoglobin (Hb). Hb+ and Hb-NO, generated in erythrocytes, were found to produce marked concentration-dependent signal intensity changes when examined by T1-, T2- and T2*-weighted MRI. Intravenous administration of ascorbic acid (3 g) to healthy volunteers, to specifically reduce any Hb+ formed during brain activation, markedly decreased fMRI signal changes during standard tasks, suggesting a blood flow-independent effect produced by the reductant. These results open a new perspective on the fMRI evaluation of physiological processes associated with task-specific activation of brain structures.
Di Salle
F
F
Institute of Radiology, University of Naples Federico II, Italy.
Barone
P
P
Hacker
H
H
Smaltino
F
F
d'Ischia
M
M
D001921:Brain / Q000502:physiology*; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D008279:Magnetic Resonance Imaging; D009569:Nitric Oxide / Q000737:chemistry*
D006454:Hemoglobins; D009569:Nitric Oxide