Diffusion tensor imaging — MRCPsych Paper A MCQ

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EasyNeuroimaging, neuroendocrinology and psychoneuroimmunologyDiffusion tensor imagingMRCPsych Paper A

A 31-year-old man undergoes diffusion tensor imaging after a traumatic brain injury to assess white-matter tract microstructural integrity. Which derived scalar measure quantifies the degree to which water diffusion is directionally constrained within these tracts?

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Correct answer: A — Fractional anisotropy

Fractional anisotropy is a scalar derived from diffusion tensor imaging that describes how strongly water diffusion is oriented in one direction. In intact, coherently organised white-matter tracts, diffusion is constrained preferentially along axons, producing relatively high fractional anisotropy; axonal or microstructural disruption may alter or reduce it. Standardised uptake value quantifies radiotracer uptake on PET. Regional cerebral blood flow is measured using perfusion techniques such as arterial spin labelling. Magnetic susceptibility is assessed using T2*-weighted or susceptibility-weighted sequences and is useful for blood products or mineral deposition. Cortical thickness is derived from structural anatomical MRI rather than diffusion tensor imaging.

Reference: Wallace EJ, Mathias JL, Ward L. Diffusion tensor imaging changes following mild, moderate and severe adult traumatic brain injury: a meta-analysis. Brain Imaging and Behavior. 2018;12(6):1607–1621. https://pubmed.ncbi.nlm.nih.gov/29383621/