| Summary: | Purpose: In vivo ³¹P MRS magnetization transfer (MT) provides a direct measure of neuronal activity at the metabolic level. This work aims to use functional ³¹P MRS-MT to investigate the change in cerebral ATP metabolic rates in healthy adults upon repeated visual stimuli.
Methods: A magnetization saturation transfer sequence with narrowband selective saturation of γ-ATP was developed for ³¹P MT experiments at 3 T.
Results: Using progressive saturation of γ-ATP, the intrinsic T1 relaxation times of phosphocreatine (PCr) and inorganic phosphate (Pi) at 3 T were measured to be 5.1±0.8 s and 3.0±1.4 s, respectively. Using steady-state saturation of γ-ATP, a significant 24±14% and 11±7% increase in the forward creatine kinase (CK) pseudo-first-order reaction rate constant, k₁, was observed upon visual stimulation in the first and second cycles respectively of a paradigm consisting of 10min-rest followed by 10min-stimulation, with the measured baseline k₁ being 0.35±0.04 s⁻¹. No significant changes in forward ATP synthase (ATPase) reaction rate, PCr/γ- ATP, Pi/γ-ATP, and NAD(H)/γ-ATP ratios, or intracellular pH were detected upon stimulation.
Conclusion: This work demonstrates the potential of studying cerebral bioenergetics using functional ³¹P MRS-MT to determine the change in the forward CK reaction rate at 3 T.
|
|---|