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Evaluation of activity-dependent functional pH and T1ρ response in the visual cortex
Hye-Young Heo1, John Wemmie2, Daniel Thedens3
1Department of Radiology, University of Iowa, Iowa City, IA 52242, USA; Department of Biomedical Engineering, University of Iowa, Iowa City, IA 52242, USA.
Neuroimage
|February 4, 2014
Summary
T1 relaxation in the rotating frame (T1ρ) primarily reflects metabolic changes in the visual cortex, not just blood flow. Higher stimulation frequencies increase T1ρ, pH, and BOLD responses, indicating activity-dependent changes.
Area of Science:
- Neuroimaging
- Metabolic Imaging
- Functional MRI
Background:
- T1 relaxation in the rotating frame (T1ρ) may detect metabolic changes in the visual cortex during tasks.
- Potential signal sources include pH, glucose, glutamate, and cerebral blood volume.
Purpose of the Study:
- To investigate the relationship between T1ρ signal changes and cerebral blood volume.
- To explore the link between T1ρ and pH changes with varying visual stimulation frequencies.
Main Methods:
- Used inferior saturation pulses to differentiate T1ρ signal contributions.
- Varied checkerboard stimulation frequency (1, 4, 7Hz) during T1ρ, BOLD, and (31)P spectroscopy imaging.
- Compared T1ρ activation areas with BOLD responses.
Main Results:
- Approximately 73% of the T1ρ signal change was attributed to in vivo metabolism.
- Increasing stimulation frequency enhanced responses across all imaging modalities.
- T1ρ activation areas largely overlapped with BOLD but were smaller; higher frequencies induced greater acidosis.
Conclusions:
- The T1ρ signal is predominantly metabolic, with a smaller contribution from cerebral blood volume.
- T1ρ and pH responses are activity-dependent, increasing with stimulation frequency, similar to BOLD signals.
