Browsing by Author "Deng, Qinbo"

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    Model of minor stroke with mild peri-infarct ischemic injury
    (Elsevier, 2016-04-29) Tuor, Ursula I.; Deng, Qinbo; Rushforth, Dave; Foniok, Taduesz; Qiao, Min
    Background Transient ischemic attack, minor stroke and stroke recurrence need improved treatment but lack animal models for research. The aim was to modify photothrombosis methods thereby producing both a minor stroke (with adjacent mild damage) or a minor recurrent stroke. New method A minor stroke, as detected using magnetic resonance imaging and histology, was produced using a low intensity beam of white light with a bright centre, a low dose of Rose Bengal and a short 5 min illumination of thinned skull. A recurrent minor stroke was produced by repeating the procedure two days later except the cortical mask was positioned 1.5 mm posteriorly. Results The minor photothrombosis procedure produced a small superficial infarct surrounded by a region of scattered necrosis detected histologically. Marked hyperintensities in diffusion weighted and T2 images identified the infarct. Peri-infarct regions with modest T2 increases corresponded to regions of scattered cell death. A recurrent minor photothrombosis produced additional damage in regions with overlapping mild injury. Comparison with existing methods Previous photothrombosis methods usually produce large cortical infarcts with little penumbra. The current method produces small infarcts with diffuse mild peri-infarct ischemic injury that can be diagnosed using T2 imaging. Conclusions The modified photothrombotic procedure will produce a minor stroke consisting of a small infarct in a region with marked diffusion and T2 hyperintensities and a peri-infarct region of selective necrosis with modest T2 changes. Minor recurrent stroke is readily produced but imaging is key for assessing size and location of each insult. Abbreviations Dw, diffusion weighted; MRI, magnetic resonance imaging; Iba1, Ionized Calcium-Binding Adapter Molecule 1; T2w, transverse relaxation time weighted; TIA, transient ischemic attack
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    Recovery Time between Multiple Mild Photothrombotic Strokes Affects Brain Damage
    (2014-02-12) Deng, Qinbo; Tuor, Ursula
    Prior to stroke, patients often experience a transient ischemic attack (TIA) or minor stroke with a high recurrence within the first week. The initial episode of ischemia, traditionally considered to causing little permanent damage to brain, is poorly understood for its role in subsequent ischemic events. We hypothesized that despite functional recovery following TIA/minor stroke, there can be sparse tissue damage that alters the brain response to a secondary mild stroke, with the final tissue fate being dependent on the recovery time between recurrent strokes. Thus, the first objective of this thesis was to establish a rat model of TIA/minor stroke using modifications of a phothothrombotic (PT) occlusion of the cerebral microvasculature. The effect of varied light intensities and illumination durations were examined on the severity of stroke. Multiple sequences (T2, Apparent Diffusion Coefficient (ADC), Perfusion Weighted Imaging) of Magnetic Resonance Imaging (MRI) were performed to evaluate the tissue damage. We found that a 5-min illumination at approximate 35,000 Lux of light intensity was optimal to produce a mild tissue damage associated with a transient ischemia measured by Laser-Doppler Flowmetry. The T2 signatures measured at 24h were good predictors of graded ischemic injury confirmed by histology. Compared with ADC measures, T2 provided a better diagnosis of mild damage (scattered necrosis). The second objective was to use this modified PT model to produce a recurrent stroke and to investigate if the outcome differed depending on the interval between insults – i.e. 1day, 2days, 3days and 1week. Using this novel model, we demonstrated that a mild recurrent stroke produced more deleterious injury with acute intervals (1 day to 3 day) than a subacute one (1week). This enhancement of damage was characterized by an increase of T2 and a decrease of perfusion. In contrast, the 1week interval produced tissue damage similar to a single mild stroke, associated with similar changes of MR. Together, our finding revealed a temporal change of brain susceptibility to ischemia, implying the importance of early treatment after TIA/minor stroke for reduction of damage with stroke recurrence.