Diffusion MRI with free gradient waveforms on a high-performance gradient system: Probing restriction and exchange in...

Area of Science:

• Neuroimaging
• Biophysics
• Diffusion MRI

Background:

• The diffusion MRI signal's dependence on diffusion time reflects restricted diffusion and exchange processes.
• Understanding these processes is crucial for interpreting diffusion MRI data in the brain.

Purpose of the Study:

• To highlight signatures of restricted diffusion and exchange in the human brain using free gradient waveforms.
• To investigate the differential time-dependence signatures in grey and white matter.

Main Methods:

• Experiments were conducted on six healthy volunteers using strong and ultra-strong gradients (80, 200, 300 mT/m).
• A set of 150 gradient waveforms with varying sensitivities to restricted diffusion and exchange was employed.
• Analysis focused on identifying unique time-dependence signatures in different brain tissues.

Main Results:

• Grey matter exhibited signatures of both restricted diffusion and exchange, while white matter showed predominantly restricted diffusion.
• Exchange in grey matter was observed to be at least twice as fast as in white matter.
• Tailored gradient waveforms successfully mapped brain exchange, with the cerebellar cortex showing short exchange times (115 ms).

Conclusions:

• Free gradient waveforms are effective for detecting in vivo time-dependence signatures of restricted diffusion and exchange.
• The developed method shows potential for clinical applications, with reduced scan times preserving contrast.
• This technique may serve as a valuable tool for studying diseased brain tissue.