Distinct MRI pattern in lesional and perilesional area after traumatic brain injury in rat — 11 months follow-up

To understand the dynamics of progressive brain damage after lateral fluid-percussion induced traumatic brain injury (TBI) in rat, which is the most widely used animal model of closed head TBI in humans, MRI follow-up of 11 months was performed. The evolution of tissue damage was quantified using MRI contrast parameters T 2 , T 1ρ , diffusion (D av ), and tissue atrophy in the focal cortical lesion and adjacent areas: the perifocal and contralateral cortex, and the ipsilateral and contralateral hippocampus. In the primary cortical lesion area, which undergoes remarkable irreversible pathologic changes, MRI alterations start at 3 h postinjury and continue to progress for up to 6 months. In more mildly affected perifocal and hippocampal regions, the robust alterations in T 2 , T 1ρ , and D av at 3 h to 3 d post-injury normalize within the next 9-23 d, and thereafter, progressively increase for several weeks. The severity of damage in the perifocal and hippocampal areas 23 d post-injury appeared independent of the focal lesion volume. Magnetic resonance spectroscopy (MRS) performed at 5 and 10 months post-injury detected metabolic alterations in the ipsilateral hippocampus, suggesting ongoing neurodegeneration and inflammation. Our data show that TBI induced by lateral fluid-percussion injury triggers long-lasting alterations with region-dependent temporal profiles. Importantly, the temporal pattern in MRI parameters during the first 23 d post-injury can indicate the regions that will develop secondary damage. This information is valuable for targeting and timing interventions in studies aiming at alleviating or reversing the molecular and/or cellular cascades causing the delayed injury

Relaxation Along a Fictitious Field (RAFF) and Z-spectroscopy using Alternating-Phase Irradiation (ZAPI) in Permanent Focal Cerebral Ischemia in Rat

Cerebral ischemia alters the molecular dynamics and content of water in brain tissue, which is reflected in NMR relaxation, diffusion and magnetization transfer (MT) parameters. In this study, the behavior of two new MRI contrasts, Relaxation Along a Fictitious Field (RAFF) and Z-spectroscopy using Alternating-Phase Irradiation (ZAPI), were quantified together with conventional relaxation parameters (T1, T2 and T1ρ) and MT ratios in acute cerebral ischemia in rat. The right middle cerebral artery was permanently occluded and quantitative MRI data was acquired sequentially for the above parameters for up to 6 hours. The following conclusions were drawn: 1) Time-dependent changes in RAFF and T1ρ relaxation are not coupled to those in MT. 2) RAFF relaxation evolves more like transverse, rather than longitudinal relaxation. 3) MT measured with ZAPI is less sensitive to ischemia than conventional MT. 4) ZAPI data suggest alterations in the T2 distribution of macromolecules in acute cerebral ischemia. It was shown that both RAFF and ZAPI provide complementary MRI information from acute ischemic brain tissue. The presented multiparametric MRI data may aid in the assessment of brain tissue status early in ischemic stroke

Correlation between changes detected by RAFF and other relaxation times.

<p>The data are pooled from all time points from the five brain regions studied. The regression lines (dashed, R² values shown) show high correlations for all parameter pairs; however, the pair T₂-RAFF is the best match to the line of unity (solid line), confirming the similarity of the time courses.</p

The measured relaxation rates in the sham-operated animals.

<p>The figures presented are mean values of areas in both hemispheres and the six time points. No systematic variation across the hemispheres, between the time points or between the animals was observed. These values agree closely with the relaxation data measured in the contralateral hemispheres of the stroke animals as well.</p

Time courses for relative ipsi-contra differences in T₂-filtered ZAPISM MT.

<p>The values of parameter S(n µs)/S(100 µs) are shown at time points one (TP1) to six (TP6) in the different brain regions S1-C3. The results from Student’s t-test are given by: p<0.05 =  † and p<0.01 =  ‡.</p