Using proton MRS/MRI of mouse
brain at 9.4 T, this work provides the first in vivo evidence of concurrent pH-dependent changes of amide
signals and related metabolic responses to hypercapnia and hypothermia. During
hypercapnia, amide MRS signals of glutamine and of unspecific compounds
increase by ≥50% at 37°C and 22°C. They are strongly correlated with
intracellular pH determined from a shift in creatine phosphokinase equilibrium.
In MRI, saturation transfer to water protons alters signal intensities in
dependence on pH and temperature. Irradiation of aliphatic compounds at -3.5
ppm frequency offset from water predominantly saturates lipids and water
associated with myelin.