Spectral Diffusion Analysis of Intravoxel Incoherent Motion MRI in Cerebral Small Vessel Disease

Abstract

Background Cerebral intravoxel incoherent motion (IVIM) imaging assumes two components. However, more compartments are likely present in pathologic tissue. We hypothesized that spectral analysis using a nonnegative least‐squares (NNLS) approach can detect an additional, intermediate diffusion component, distinct from the parenchymal and microvascular components, in lesion‐prone regions. Purpose To investigate the presence of this intermediate diffusion component and its relation with cerebral small vessel disease (cSVD)‐related lesions. Study Type Prospective cross‐sectional study. Population Patients with cSVD (n = 69, median age 69.8) and controls (n = 39, median age 68.9). Field Strength/Sequence Whole‐brain inversion recovery IVIM acquisition at 3.0T. Assessment Enlarged perivascular spaces (PVS) were rated by three raters. White matter hyperintensities (WMH) were identified on a fluid attenuated inversion recovery (FLAIR) image using a semiautomated algorithm. Statistical Tests Relations between IVIM measures and cSVD‐related lesions were studied using the Spearman's rank order correlation. Results NNLS yielded diffusion spectra from which the intermediate volume fraction fint was apparent between parenchymal diffusion and microvasular pseudodiffusion. WMH volume and the extent of MRI‐visible enlarged PVS in the basal ganglia (BG) and centrum semiovale (CSO) were correlated with fint in the WMHs, BG, and CSO, respectively. fint was 4.2 ± 1.7%, 7.0 ± 4.1% and 13.6 ± 7.7% in BG and 3.9 ± 1.3%, 4.4 ± 1.4% and 4.5 ± 1.2% in CSO for the groups with low, moderate, and high number of enlarged PVS, respectively, and increased with the extent of enlarged PVS (BG: r = 0.49, P < 0.01; CSO: r = 0.23, P = 0.02). fint in the WMHs was 27.1 ± 13.1%, and increased with the WMH volume (r = 0.57, P < 0.01). Data Conclusion We revealed the presence of an intermediate diffusion component in lesion‐prone regions of cSVD and demonstrated its relation with enlarged PVS and WMHs. In tissue with these lesions, tissue degeneration or perivascular edema can lead to more freely diffusing interstitial fluid contributing to fint. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:1170–1180.

Neurofluid Dynamics and the Glymphatic System: A Neuroimaging Perspective

“…Another study utilized the intravoxel incoherent motion (IVIM) method to investigate the intermediate diffusion component using a nonnegative least-squares method to evaluate glymphatic system function. Using this method, values for both parenchymal diffusivity and microvascular perfusion were detected and perivascular fluid motion was evaluated in relation to the glymphatic system ( 43 ). Diffusion study can also be applied not only to the brain parenchyma but also to the CSF space.…”

“…One study showed the relationship between the volume fraction of the intermediate diffusion component with white matter hyperintensities and enlarged perivascular spaces. This correlation could indicate aberrant amounts of ISF in degenerated tissue or perivascular edema preceding tissue degeneration in cases with small vessel disease ( 43 ).…”

Assessment of microvascular rarefaction in human brain disorders using physiological magnetic resonance imaging

“…movement of interstitial fluid, 140 , 142 BBB leakage, 137 , 143 and vessel tortuosity. 144 Since rarefaction is often linked with one or more of these vascular alterations, the IVIM perfusion measures ( f , D* and fD* ) are rather indicative of microvascular integrity than mere CBF.…”

Current Concepts in Intracranial Interstitial Fluid Transport and the Glymphatic System: Part II—Imaging Techniques and Clinical Applications

“…Intravoxel incoherent motion MRI, which acquires diffusion-weighted images for multiple b values and fits multiple exponentials that typically correspond to capillary perfusion and Brownian motion, has also been extended to assess for glymphatic function (23). The presence of a diffusion component intermediate to parenchymal diffusivity and microvascular perfusion in regions surrounding enlarged perivascular spaces (EPVS) and white matter hyperintensities has been detected, which may relate to regional glymphatic dysfunction (Fig 2A) (24). PVS flows have also been assessed using diffusion tensor imaging techniques.…”