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Probing mouse brain microstructure using oscillating gradient diffusion MRI
Manisha Aggarwal1, Melina V Jones, Peter A Calabresi
1Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Abstract:
High resolution diffusion tensor images of the mouse brain were acquired using the pulsed gradient spin echo sequence and the oscillating gradient spin echo sequence. The oscillating gradient spin echo tensor images demonstrated frequency-dependent changes in diffusion measurements, including apparent diffusion coefficient and fractional anisotropy, in major brain structures. Maps of the rate of change in apparent diffusion coefficient with oscillating gradient frequency revealed novel tissue contrast in the mouse hippocampus, cerebellum, and cerebral cortex. The observed frequency-dependent contrasts resembled neuronal soma-specific Nissl staining and nuclei-specific 4',6-diamidino-2-phenylindole (DAPI) staining in the mouse brain, which suggests that the contrasts might be related to key features of cytoarchitecture in the brain. In the mouse cuprizone model, oscillating gradient spin echo-based diffusion MRI revealed significantly higher frequency-dependence of perpendicular diffusivity (λ(⊥) ) in the demyelinated caudal corpus callosum at 4 weeks after cuprizone treatment when compared with control mice and mice at 6 weeks after cuprizone treatment. The elevated frequency-dependence of λ(⊥) coincided with the infiltration of activated microglia/macrophages and disruption of axons during acute demyelination in the caudal corpus callosum. The results demonstrate the potential of oscillating gradient spin echo-based diffusion MRI for providing tissue contrasts complimentary to conventional pulsed gradient spin echo-based diffusion MRI.
Insights
Oscillating gradient spin echo MRI reveals novel brain tissue contrasts and frequency-dependent diffusion changes. This technique shows potential for enhanced imaging in demyelination models, complementing standard diffusion MRI.
Area of Science:
- Neuroimaging
- Biophysics
- Diffusion MRI
Background:
- Diffusion tensor imaging (DTI) provides insights into brain microstructure.
- Conventional pulsed gradient spin echo (PGSE) DTI has limitations in resolving certain tissue properties.
Purpose of the Study:
- To investigate the utility of oscillating gradient spin echo (OGSE) diffusion MRI for generating novel tissue contrasts in the mouse brain.
- To explore frequency-dependent diffusion changes in major brain structures and in a demyelination model.
Main Methods:
- Acquisition of high-resolution diffusion tensor images using both PGSE and OGSE sequences in mouse brains.
- Analysis of frequency-dependent changes in apparent diffusion coefficient (ADC) and fractional anisotropy (FA).
- Comparison of OGSE-derived contrasts with Nissl and DAPI staining, and assessment in a cuprizone-induced demyelination model.
Main Results:
- OGSE tensor imaging revealed frequency-dependent diffusion changes in major brain structures.
- Novel tissue contrasts, resembling cytoarchitectural features, were observed in the hippocampus, cerebellum, and cerebral cortex.
- Elevated frequency-dependence of perpendicular diffusivity (λ(⊥)) was detected in demyelinated corpus callosum during acute stages of cuprizone treatment, correlating with microglial infiltration and axonal damage.
Conclusions:
- OGSE-based diffusion MRI offers unique tissue contrasts complementary to conventional PGSE-based DTI.
- The observed frequency-dependent contrasts may relate to specific cytoarchitectural features of brain tissue.
- OGSE MRI shows promise for characterizing microstructural changes in demyelination and other neurological conditions.
