Diffusion and perfusion magnetic resonance imaging following closed head injury in rats

Diffusion-, perfusion-, T-1-, and T-2-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 overestim ate the histological damage, In the first 2 h, the histological damage seem s to be a superposition of abnormalities in the T1- and diffusion-weighted images, In areas with more than 10% reduction in the apparent diffusion coe fficients (ADCs), reduced regional cerebral blood volume (r-CBV) was also o bserved. The decrease in ADCs and rCBV correlated with r = 0.78. Changes in the MRI parameters revealed the following: (a) Further reduction in ADC oc curred from 83 +/- 15% at 1-2 h after trauma to 69 +/- 9% at 24 h, and 1 we ek later a marked elevation in the ADC values is observed. (b) Blood perfus ion 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 posti mpact, areas of hyper- and hypoperfusion were observed, One week later, sim ilar perfusion was found in both hemispheres of all rats, (c) T-2 hyperinte nsity at 24 h overestimated the histological damage found at 1 week. At one week following the trauma, the T-2 hyperintensity underestimated the histo logical 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 T-1 and on the diffusion-weighted MR images at ea rly time point represents best the histological damage. Both T-2 and rCBV i mages are less informative in terms of actual histological damage.