Diffusion and Perfusion Magnetic Resonance Imaging Following Closed Head Injury in Rats

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Abstract
Diffusion-, perfusion-, T1-, and T2-weighted magnetic resonance imaging (MRI) were performed at 1–2 h, 24 h, and 1 week following closed head injury (CHI) in rats, and data was compared with hematoxylin and eosin histology. At 1–2 h, large areas of low perfusion in the damaged hemisphere overestimate the histological damage. In the first 2 h, the histological damage seems to be a superposition of abnormalities in the T1- and diffusion-weighted images. In areas with more than 10% reduction in the apparent diffusion coefficients (ADCs), reduced regional cerebral blood volume (r-CBV) was also observed. The decrease in ADCs and rCBV correlated with r = 0.78. Changes in the MRI parameters revealed the following: (a) Further reduction in ADC occurred from 83 ± 15% at 1–2 h after trauma to 69 ± 9% at 24 h, and 1 week later a marked elevation in the ADC values is observed. (b) Blood perfusion measurements performed 1–2 h posttrauma revealed a pronounced reduction in r-CBV (53 ± 18%) in the damaged hemisphere in all rats. At 24 h postimpact, areas of hyper- and hypoperfusion were observed. One week later, similar perfusion was found in both hemispheres of all rats. (c) T2 hyperintensity at 24 h overestimated the histological damage found at 1 week. At one week following the trauma, the T2 hyperintensity underestimated the histological damage. It is concluded that CHI, which is a heterogeneous insult, should be studied by a combination of MRI techniques. The superposition of the abnormalities seen on T1 and on the diffusion-weighted MR images at early time point represents best the histological damage. Both T2 and rCBV images are less informative in terms of actual histological damage.