Oscillating gradient spin echo diffusion time effects implicate variations in neurite beading for the heterogeneous...

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Diffusion MRI (dMRI) is crucial for detecting acute ischemic stroke.
• Neurite beading and swelling are hypothesized mechanisms for reduced diffusion in stroke.
• The diffusion time dependence of these changes remains incompletely understood.

Purpose of the Study:

• To investigate the heterogeneity of diffusion time effects in ischemic stroke lesions.
• To explore the microstructural basis of these effects using Monte Carlo simulations.
• To compare diffusion MRI metrics between short and long diffusion times in stroke.

Main Methods:

• Acquired Pulsed Gradient Spin Echo (PGSE) and Oscillating Gradient Spin Echo (OGSE) dMRI at 3T in 39 acute stroke patients.
• Compared mean, axial, and radial diffusivity differences (ΔMD/ΔAD/ΔRD) between lesion and contralateral tissues.
• Utilized Monte Carlo simulations of beaded axons with experimental waveforms to model neurite morphology effects.

Main Results:

• Mean diffusivity (MD) reduction was greater with PGSE (-40%) than OGSE (-29%) in lesions.
• The diffusion time effect (ΔMD) was significantly larger in lesions compared to contralateral white matter.
• Simulations indicated larger beading amplitude and intracellular volume fraction in lesions, particularly in the internal capsule and corona radiata.

Conclusions:

• Ischemic regions exhibit greater diffusion time-dependent diffusivity changes, correlating with larger axon diameters.
• Monte Carlo simulations support that pronounced differences between OGSE and PGSE are characteristic of large, beaded axons.
• This study elucidates the microstructural underpinnings of diffusion alterations in acute stroke.