Characterisation of microvessel blood velocity and segment length in the brain using multi-diffusion-time diffusion-weighted MRI

J Cereb Blood Flow Metab. 2021 Aug;41(8):1939-1953. doi: 10.1177/0271678X20978523. Epub 2020 Dec 16.


Multi-diffusion-time diffusion-weighted MRI can probe tissue microstructure, but the method has not been widely applied to the microvasculature. At long diffusion-times, blood flow in capillaries is in the diffusive regime, and signal attenuation is dependent on blood velocity (v) and capillary segment length (l). It is described by the pseudo-diffusion coefficient (D*=vl/6) of intravoxel incoherent motion (IVIM). At shorter diffusion-times, blood flow is in the ballistic regime, and signal attenuation depends on v, and not l. In theory, l could be estimated using D* and v. In this study, we compare the accuracy and repeatability of three approaches to estimating v, and therefore l: the IVIM ballistic model, the velocity autocorrelation model, and the ballistic approximation to the velocity autocorrelation model. Twenty-nine rat datasets from two strains were acquired at 7 T, with b-values between 0 and 1000 smm-2 and diffusion times between 11.6 and 50 ms. Five rats were scanned twice to assess scan-rescan repeatability. Measurements of l were validated using corrosion casting and micro-CT imaging. The ballistic approximation of the velocity autocorrelation model had lowest bias relative to corrosion cast estimates of l, and had highest repeatability.

Keywords: Blood velocity; diffusion time; intravoxel incoherent motion; microvessel structure; velocity autocorrelation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Flow Velocity / physiology*
  • Brain / blood supply
  • Brain / diagnostic imaging*
  • Diffusion Magnetic Resonance Imaging / methods*
  • Image Interpretation, Computer-Assisted
  • Microvessels / physiology*
  • Models, Biological
  • Rats
  • Rats, Inbred F344
  • Signal-To-Noise Ratio
  • X-Ray Microtomography