Temporal evolution of ischemic damage in rat brain measured by proton nuclear magnetic resonance imaging.

Abstract

We studied the effect of focal cerebral ischemia on the "state" of brain water using proton nuclear magnetic resonance imaging. Focal cerebral ischemia was induced in five halothaneanesthetized rats via tandem occlusion of the left common carotid artery and the left middle cerebral artery. The proton transverse relaxation time, the proton density, and the water diffusion coefficient were measured at various times from the same region of brain tissue from 1.5 to 168 hours after occlusion. Early measurements indicated significant changes in the transverse relaxation time (p=0.004) and water diffusion coefficient (/>=0.002) of ischemic brain tissue compared with a homologous region from the contralateral hemisphere. However, the transverse relaxation time, proton density, and water diffusion coefficient in ischemic brain tissue showed different temporal evolutions over the study period. Diffusion coefficient weighting was superior to relaxation time and proton density weighting for the visualization of early cerebral ischemia. Our data suggest that nuclear magnetic resonance imaging is sensitive in detecting changes in proton-associated parameters during early cerebral ischemia and confirm significant changes (p^O.Ol) in the temporal evolution of transverse relaxation times, proton densities, and diffusion coefficients following middle cerebral artery occlusion. (Stroke 1991^2:802-808) N uclear magnetic resonance (NMR) offers the ability to assess noninvasively several physical parameters that are directly related to the amount and "state" of water in brain tissue. The spin-spin relaxation time (T 2 ) is exquisitely sensitive to the relatively slow motions (i.e., rotation of proteins) of the system. Proton density (p) images reveal the spatial distribution of the number of NMR-visible nuclei in the tissue. More recently, NMR has been used to generate images the contrast of which is based on the diffusion coefficient of water (D w ). '-4 We document the temporal evolution of changes in T 2 , p, and D w following occlusion of the middle cerebral artery (MCA) in rats. These measurements provide new information regarding the relative time course of changes in these parameters in experimental ischemia Received August 20, 1990; accepted February 8, 1991. based on the physical properties of water. Characterization of the time course of these NMR-measurable parameters, for both normal and ischemic brain tissue, may provide new insight into the mechanisms responsible for ischemic brain damage and cerebral edema.Comparison of the various types of images may be clinically useful when the physical basis of these changes is more thoroughly understood. Materials and MethodsFive fasted adult male Fisher rats weighing 175-250 g were anesthetized with an inhaled mixture of 69% N 2 O, 30% Oj, and 1.0-1.5% halothane. The rats were allowed to breathe spontaneously throughout all surgical and NMR procedures. Focal cerebral ischemia was induced using tandem occlusion of the left common carotid artery and the left MCA, similar to t...

Temporal profile of T2-Weighted MRI Distinguishes between Pannecrosis and Selective Neuronal Death after Transient Focal Cerebral Ischemia in the Rat

“…In shorter follow-up MR time series after MCAO (7 days), incomplete recovery of T 1 and T 2 values has been observed in some studies after transient (Neumann-Haefelin et al, 2000) and even permanent (Helpern et al, 1993;Knight et al, 1991) MCAO in rats. Knight et al (1994) described a heterogeneous response of MR relaxation times to MCAO, and noted large increases in T 2 times in the dorsolateral striatum with only moderate histological damage.…”

Regional and temporal variations in tissue sodium concentration during the acute stroke phase

“…Indeed, large deviations have been observed between areas with decreased apparent diffusion coefficient (ADC) compared to infarct determined by the gold standard technique of histology after stroke (4). Furthermore, ADC values have also been observed to normalize in areas of permanently damaged tissue during the subacute phase (5,6). Because conventional MR techniques demonstrate such ambiguities, we still lack an early direct and noninvasive marker for irreversibly damaged tissue.…”

Pharmacologic Reversal of Acute Changes in Diffusion-Weighted Magnetic Resonance Imaging in Focal Cerebral Ischemia

“…One of the primary determinants of dif fusion is temperature. Although ischemic brain tis sue may drop in temperature by 1-2aC (Busto et al, 1987), this is unlikely to be the major cause of DWI change since 1-2aC drops in temperature lead to only 3-4% changes in diffusion coefficients (LeBi han et aI., 1991), whereas ischemia decreases diffu sion coefficients by 50--60% below normal values (Knight et al, 1991). Another possibility is the lack of tissue pulsatility in ischemic brain, leading to less micro vibrations and a decreased level of signal loss in DWI scans (Mintorovitch et al, 1991).…”