fMRI at Ultra High Field

Researchers from the Netherlands and Israel have investigated the relationship between magnetic field strength and functional magnetic resonance imaging (fMRI) signal. For this they implemented fMRI using blood oxygenation level-dependent (BOLD) contrast to measure neuronal activity through oxygenation changes and cerebral blood volume (CBV). They conclude that in addition to the increased contrast-to-noise ratio (CNR), the use of ultra-high magnetic fields for fMRI will provide a new perspective to processes within the brain.

Using non-invasive in vivo fMRI to approach invasive vascular physiology study knowledge will be a crucial next step in advancing understanding of brain function in both animals and humans. Because the fMRI signal is dependent on the amount of deoxygenated hemoglobin, which can be visualized via the blood oxygenation level-dependent (BOLD) effect, and to the cerebral blood volume (CBV), fMRI can detect changes in blood flow related to brain activity, allowing researchers to understand which regions of the brain are more active than others.

While further research is required, the study by Uludağ and Blinder demonstrates the possibility of utilizing non-invasive fMRI for a better understanding of vascular processes that result from functional stimulation.

The Ultra-high Field Advantage

Thermal noise dominated high resolution fMRI of brain physiology benefits from ultra-high field (UHF), achieving a significant sensitivity gain compared to lower magnetic fields. With a standard spatial resolution of 2-4 mm isotropric, and using gradient-echo (GE) and spin-echo (SE) methods, fMRI at 7 Tesla showed a 35% signal increase over the same measurements at 3 Tesla. With increasing resolution, and the corresponding thermal noise dominance, this signal gain increases supra-linearly to 6 fold for 7 Tesla vs 3 Tesla. Reduced partial volume effects of these small voxels promise even further improvements for high-resolution fMRI.

The significant signal-to-noise and sensitivity improvements made possible by UHF enable a more complete view of the brain to be achieved, paving the way to a more advanced understanding of neurological processes within the human brain.

Read the full paper here

Uludağ, K. and Blinder, P., 2018. Linking brain vascular physiology to hemodynamic response in ultra-high field MRI. Neuroimage, 168, pp.279-295.