Diffusion-weighted imaging studies of cerebral ischemia in gerbils. Potential relevance to energy failure.

Abstract

Background and Purpose: Diffusion-weighted magnetic resonance imaging has been shown to be particularly suited to the study of the acute phase of cerebral ischemia in animal models. The studies reported in this paper were undertaken to determine whether this technique is sensitive to the known ischemic thresholds for cerebral tissue energy failure and disturbance of membrane ion gradients.Methods: Diffusion-weighted images of the gerbil brain were acquired under two sets of experimental conditions: as a function of cerebral blood flow after controlled graded occlusion of the common carotid arteries (partial ischemia), as a function of time following complete bilateral carotid artery occlusion (severe global ischemia), and on deocclusion after 60 minutes of ischemia.Results: During partial cerebral ischemia, the diffusion-weighted images remained unchanged until the cerebral blood flow was reduced to 15-20 ml • 100 g" 1 • min~' and below, when image intensity increased as the cerebral blood flow was lowered further. This is similar to the critical flow threshold for maintenance of tissue high-energy metabolites and ion homeostasis. After the onset of severe global cerebral ischemia, diffusion-weighted image intensity increased gradually after a delay of approximately 2.5 minutes, consistent with complete loss of tissue adenosine triphosphate and with the time course of increase in extracellular potassium. This hyperintensity decreased on deocclusion following 60 minutes of ischemia.Conclusions: The data suggest that diffusion-weighted imaging is sensitive to the disruption of tissue energy metabolism or a consequence of this disruption. This raises the possibility of imaging energy failure noninvasively. In humans, this could have potential in visualizing brain regions where energy metabolism is impaired, particularly during the acute phase following stroke. (Stroke 1992;23:1602-1612 KEY WORDS • cerebral ischemia • energy metabolism • magnetic resonance imaging • gerbils

ADC characterization of region‐specific response to cerebral perfusion deficit in rats by MRI at 9.4 T

“…However, the bulk of MRI data on small animals at high magnetic fields (7 T and above) is being generated using vertical magnets (9,15 (15,24) were estimated to affect only marginally the results of CBF calculations from our perfusion data using Eq. [1]. The expected deviation should not exceed about 7%, which falls within the experimental error of the perfusion measurements, and thus should not change the character of the CBF curves presented in Figs.…”

“…The apparent diffusion coefficient (ADC) of water, which is measurable noninvasively by MRI, has been proposed as a reliable parameter for early detection of brain ischemia (1)(2)(3). ADC was shown to be sensitive to acute ischemia within minutes of occurrence (4).…”

Inverse mismatch and lesion growth in small subcortical ischaemic stroke

“…At first sight this might seem surprising as it is has been shown in territorial ischaemia that ADC drops occur at a brain perfusion level below 34 ml/100g/min in rats [33] and below 15-20 ml/100g/min in gerbils [34]. On the other hand, ischaemia is obviously not the only "path" to cell damage.…”

Cerebral Diffusion and T2: MRI Predictors of Acute Mountain Sickness during Sustained High-Altitude Hypoxia

“…30 Apparent diffusion coefficient does not decrease until oxygen delivery decreases below levels critical for maintenance of Na þ -K þ ATPase activity. 31 Reversible decreases in ADC are seen in the tissues immediately surrounding an infarct (the penumbra) 23 and these represent areas of brain in which there is temporary interruption of Na þ -K þ ATPase, but not sufficient to cause Na þ -K þ ATPase failure and disrupted ionic homeostasis. 32 We speculate that a similar mechanism seen in the penumbra underlies the reversible ADC changes seen here during symptomatic hypoxia.…”