Magnetic resonance imaging indicators of blood-brain barrier and brain water changes in young rats with kaolin-induced hydrocephalus

Abstract

BackgroundHydrocephalus is associated with enlargement of cerebral ventricles. We hypothesized that magnetic resonance (MR) imaging parameters known to be influenced by tissue water content would change in parallel with ventricle size in young rats and that changes in blood-brain barrier (BBB) permeability would be detected.MethodsHydrocephalus was induced by injection of kaolin into the cisterna magna of 4-week-old rats, which were studied 1 or 3 weeks later. MR was used to measure longitudinal and transverse relaxation times (T1 and T2) and apparent diffusion coefficients in several regions. Brain tissue water content was measured by the wet-dry weight method, and tissue density was measured in Percoll gradient columns. BBB permeability was measured by quantitative imaging of changes on T1-weighted images following injection of gadolinium diethylenetriamine penta-acetate (Gd-DTPA) tracer and microscopically by detection of fluorescent dextran conjugates.ResultsIn nonhydrocephalic rats, water content decreased progressively from age 3 to 7 weeks. T1 and T2 and apparent diffusion coefficients did not exhibit parallel changes and there was no evidence of BBB permeability to tracers. The cerebral ventricles enlarged progressively in the weeks following kaolin injection. In hydrocephalic rats, the dorsal cortex was more dense and the white matter less so, indicating that the increased water content was largely confined to white matter. Hydrocephalus was associated with transient elevation of T1 in gray and white matter and persistent elevation of T2 in white matter. Changes in the apparent diffusion coefficients were significant only in white matter. Ventricle size correlated significantly with dorsal water content, T1, T2, and apparent diffusion coefficients. MR imaging showed evidence of Gd-DTPA leakage in periventricular tissue foci but not diffusely. These correlated with microscopic leak of larger dextran tracers.ConclusionsMR characteristics cannot be used as direct surrogates for water content in the immature rat model of hydrocephalus, probably because they are also influenced by other changes in tissue composition that occur during brain maturation. There is no evidence for widespread persistent opening of BBB as a consequence of hydrocephalus in young rats. However, increase in focal BBB permeability suggests that periventricular blood vessels may be disrupted.

Diffusion Tensor Imaging Properties and Neurobehavioral Outcomes in Children with Hydrocephalus

“…9, 11, 12, 23, 24 In DWI studies, hydrocephalus was often found to be associated with abnormally high ADC values in PVWM. 23-25 In DTI studies, lower FA values have been consistently found in the corpus callosum in hydrocephalus, while mixed FA changes have been reported in some other white matter structures, such as the internal capsule. 9-12 …”

A Multicenter Preclinical MRI Study: Definition of Rat Brain Relaxometry Reference Maps

“…They show that T1 relaxation time increases with magnetic field while T2 relaxation time decreases (de Graaf et al, 2006, Wright et al, 2008, van de Ven et al, 2007. Some values have been reported in the literature for few brain regions (Barbier et al, 2005, Behroozi et al, 2018, Cremillieux et al, 1998, Del Bigio et al, 2011, Gigliucci et al, 2014, Koundal et al, 2015, Liachenko and Ramu, 2017, Suleymanova et al, 2014, but no consensus has been reached yet about values of reference for specific rat brain regions. To define such reference maps, a large number of brain structures or regions should be considered and a sufficient number of animals should be included to reflect inter-individual variability.…”

In vivo measurement of T1 and T2 relaxation times in awake pigeon and rat brains at 7T

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