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Incidence of apparent restricted diffusion in three different models of cerebral infarction
D G Norris1, T Niendorf, M Hoehn-Berlage
1Fachbereich Chemie, Universität Bremen, Germany.
Abstract:
High speed magnetic resonance imaging (MRI) and short diffusion times are used to investigate the appearance of restricted diffusion in three different models of cerebral infarction. The models are: the middle cerebral artery occlusion (MCAO) model in the rat, the carotid occlusion model in the gerbil, and the Rose Bengal microvascular occlusion model in the rat. All three were investigated for 16 b-values equally spaced between 10 and 1510 s/mm2 using two distinct experiments. In the ct (constant time) experiment, the diffusion time was held constant at 11.7 ms while the b-value was varied with the gradient strength. In the cg (constant gradient) experiment, the gradient strength was held constant and the b-value increased by varying the diffusion time from 4.4 to 11.7 ms. A monoexponential decay of the signal intensity with b-value in the ct experiment accompanied by nonmonoexponential (NME) decay in the cg experiment is indicative of restricted diffusion. As this phenomenon is detectable only at short diffusion times, it cannot be due to restriction by impermeable membranes, and we have thus termed this apparent restriction. For the MCAO model and the carotid occlusion model, apparent restriction was found both inside the infarct territory and in some regions outside it. No definite evidence for restriction was found for the Rose Bengal model, which was, however, only studied from 24 h post-insult.
Insights
Apparent diffusion restriction in cerebral infarction models was detected using high-speed MRI and short diffusion times. This phenomenon, observed in middle cerebral artery occlusion and carotid occlusion models, suggests rapid changes within brain tissue post-stroke.
Area of Science:
- Neuroimaging
- Cerebrovascular Diseases
- Magnetic Resonance Imaging
Background:
- Cerebral infarction, or stroke, involves restricted diffusion detectable by MRI.
- Understanding diffusion changes at short diffusion times is crucial for early stroke detection.
Purpose of the Study:
- To investigate apparent diffusion restriction in various cerebral infarction models using high-speed MRI.
- To differentiate true diffusion restriction from apparent restriction at short diffusion times.
Main Methods:
- Utilized high-speed magnetic resonance imaging (MRI) with short diffusion times.
- Employed two experimental protocols: constant time (ct) and constant gradient (cg) experiments.
- Examined three models: middle cerebral artery occlusion (MCAO) in rats, carotid occlusion in gerbils, and Rose Bengal model in rats.
Main Results:
- Apparent diffusion restriction was observed in MCAO and carotid occlusion models, both within and outside infarct territories.
- Non-monoexponential (NME) signal decay in the constant gradient (cg) experiment at short diffusion times indicated apparent restriction.
- The Rose Bengal model showed no definitive evidence of restriction, possibly due to later study time.
Conclusions:
- Apparent diffusion restriction is detectable at short diffusion times in specific cerebral infarction models.
- This phenomenon is distinct from restriction by impermeable membranes and provides insights into early stroke pathophysiology.
- High-speed MRI with short diffusion times is a valuable tool for studying acute ischemic changes.
