Rat Brain Global Ischemia–Induced Diffusion Changes Revisited: Biophysical Modeling of the Water and NAA MR "Diffusion Signal". Issue 3 (22nd April 2022)

• Record Type: Journal Article
• Authors: Spees, William M.; Sukstanskii, Alex L.; Bretthorst, G. Larry; Neil, Jeffrey J.; Ackerman, Joseph J.H.
• Is Part Of: Magnetic resonance in medicine. Volume 88:Issue 3(2022)
• Page Start: 1333
• Page End: 1346
• Publication Date: 2022-04-22
• Subjects: intraneuronal viscosity -- metabolite diffusion -- N‐acetyl aspartate -- stroke; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.29262
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: To assess changes in intracellular diffusion as a mechanism for the reduction in water ADC that accompanies brain injury. Using NAA as a marker of neuronal cytoplasmic diffusion, NAA diffusion was measured before and after global ischemia (immediately postmortem) in the female Sprague–Dawley rat. Methods: Diffusion‐weighted PRESS spectra, with diffusion encoding in a single direction, were acquired from large voxels of rat brain gray matter in vivo and postischemia employing either pairs of pulsed half‐sine–shaped gradients (in vivo and postischemia, b max = 19 ms/μm 2 ) or sinusoidal oscillating gradients (in vivo only) with frequencies of 99.2–250 Hz. A 2D randomly oriented cylinder (neurite) model gave estimates of longitudinal and transverse diffusivities ( D L and D T, respectively). In this model, D L represents the "free" diffusivity of NAA, whereas D T reflects highly restricted diffusion. Using oscillating gradients, the frequency dependence of D T [ D T (ω)] gave estimates of the cylinder (axon/dendrite) radius. Results: A 10% decrease in D L, NAA followed global ischemia, dropping from 0.391 ± 0.012 μm 2 /ms to 0.350 ± 0.009 μm 2 /ms. Modeling D T, NAA (ω) provided an estimate of the neurite radius of 1.0 ± 0.6 μm. Conclusion: Whereas the increase in apparent intraneuronal viscosity suggested by changes in D L, NAA may contribute to the overall reduction in water ADC associated with brain injury, it is not sufficient to be the sole explanation. Estimates of neurite radius based on D T (ω) were consistent with literature values.