Magnetic Resonance Imaging (MRI) plays a central role in clinical diagnostic care and basic neuroscience research and MRI technology continues to evolve at a rapid pace. Our lab is focused on MRI technology improvements for neuroimaging. Along with improvements in imaging speed and resolution we develop new types of image contrast that allow us to visualize previously undectable features of healthy and diseased brain tissue.
Ultra High-Field (7T) MRI
The sensitivity of the MRI scales approximately linearly with the strength of the main magnetic field and therefore there is a continuous drive towards developing MRI systems with stronger magnetic fields. The current standard for clinical MRI scanners is 1.5T or 3T. The R.M. Lucas Center for Imaging at Stanford University houses a 7T human MRI scanner (one of only ~50 such scanners in the world). This ultra high field MRI scanner provides dramatically improved sensitivity, contrast and spectral dispersion.
Stronger, Faster Gradients
Another aspect of MRI hardware that has seen recent improvements are the magnetic gradients used for spatial encoding. The highly publicized NIH Human Connectome Project funded the construction of human 3T MRI scanners equipped with 100 mT/m and 300 mT/m maximum gradient strengths compared to the standard 40-70 mT/m gradients used in conventional clinical MRI scanners.
Cortical Diffusion Imaging
Diffusion anisotropy measurements are most commonly exploited for the purpose of mapping white matter structural connections. At conventional diffusion MRI resolutions (8-27 mm3 voxels) grey matter (GM) does not exhibit a coherent pattern of diffusion anisotropy. Only recently, as diffusion studies have started to push to higher spatial resolutions, have cerebral cortical GM diffusion anisotropy patterns have been revealed in the mature human brain.
Mapping Axon Diameter
The diameter of an axon is proportional to the speed at which action potentials are conducted along its length. Therefore any change in the distributions of axon diameters in a white matter tract impacts the operation of networks that are distributed across the brain.
Ex Vivo Diffusion Imaging
In vivo diffusion imaging suffers from modest interpretability and an incomplete understanding of how tissue biology affects the diffusion signal. Therefore, diffusion imaging of ex vivo brains provides a valuable link between in vivo diffusion studies and histology.
Diffusion-Weighted Steady-State Free Precession
Steady-state diffusion-weighted imaging (DW) has long been recognized to offer potential benefits over conventional spin-echo methods. This family of pulse sequences is highly efficient and compatible with three-dimensional acquisitions, which could enable high-resolution, low-distorotion images.
Resting-State fMRI at 7T
Resting-state FMRI is a method for non-invasively investigating brain functional connectivity when a subject is at rest. Stronger main magnetic fields increase both the signal-to-noise ratio and contrast-to-noise (CNR) for resting-state FMRI. This increased SNR and CNR can be used to map brain connectivity at higher spatial and/or temporal resolutions.