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Publication Detail
Optimised oscillating gradient diffusion MRI for the estimation of axon radius in an ex vivo rat brain
  • Publication Type:
  • Authors:
    Siow BMCW, Ianus A, Drobnjak I, Christie IN, Lythgoe MF, Alexander DC
  • Publication date:
  • Volume:
    Vol. 20 (Abstract 0357)
  • Name of conference:
    20th Annual Meeting of The International Society for Magnetic Resonance in Medicine
  • Conference place:
    Melbourne, Australia
  • Conference start date:
  • Conference finish date:
  • Keywords:
    Diffusion MRI, Microstructure, OGSE, oscillating gradient
We adapt the ActiveAx orientationally invariant axon radius index technique [1,2] for oscillating gradient spin-echo (OGSE) diffusion MRI. Reliable estimates of small axon radii (<5 ┬Ám) require high gradient amplitudes and short diffusion times, which limits the suitability of pulsed gradient spin-echo (PGSE) sequences for microstructure estimates in a clinical setting. OGSE sequences have shorter diffusion times and thus can probe shorter length scales [3-8]. A recent in silico study [8] suggests that the optimal gradient waveform for pore-size estimation, particularly for small radii, consists of oscillating trapezoids; [9] provides empirical support. In this study, we adapt the algorithm in [1] to optimize three separate protocols for axon radius index mapping with ActiveAx. The protocols are constructed from different types of OGSE sequences: sine normal (SN), cosine reversed (CR), and square wave(SW), as illustrated in Figure 1.We implemented these protocols on a 9.4T pre-clinical system and imaged an ex-vivo rat brain. We subsequently performed microstructure parameter fits for voxels in the corpus callosum. Parameter estimates were consistent across all OGSE protocols, producing highest radius index in the midbody. In addition, we found that the SWOGSE protocol consistently produced the narrowest posterior distributions on the fitted parameters, supporting the expected increase in sensitivity to the microstructural parameters.
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