Development of real-time, non-invasive photoacoustic imaging to rapidly detect and track perinatal focal stroke at birth

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Perinatal arterial ischemic stroke is estimated to occur in 1/2300–1/5000 live births and can result in long-term deficits in motor, cognitive, attention, and executive functions and persistent seizures. Rapid diagnosis of focal ischemic stroke in newborns, the timing of the stroke, and differentiation of perinatal stroke from global hypoxia-ischemia allow more efficient and directed interventions/prognosticacions. In the proposed work, we will develop miniaturized noninvasive photoacoustic imaging for use on the scalp of human fetuses and newborns to dynamically track changes in oxygenation in sagittal sinus venous blood and regional cortical tissue both during and after labor. Using a newborn animal with a large gyrencephalic brain, we will validate the oxygenation measurements against directly measured sagittal sinus O2 saturation during hypoxia-ischemia and against pimonidazole-based measurements of regional tissue hypoxia during focal stroke. Based on these data, we will then develop algorithms for detecting graded progressive ischemia based on tissue hemoglobin content and O2 saturation. We will test the sensitivity and specificity of these algorithms with different size and locations of photothrombotic-induced stroke. Furthermore, secondary injury cascades that transpire in the immature brain after arterial thrombotic stroke may differ from those that transpire in mature brain and likely depend on maturation of connectivity and energy metabolism in specific brain regions. After photothrombosis of the middle cerebral artery, we will contrast dynamic changes in tissue hemoglobin content and O2 saturation in 1) the metabolically active primary sensorimotor cortex, known to be selectively vulnerable to hypoxia- ischemia, 2) the metabolically quiescent secondary sensorimotor cortex known to be resistant to hypoxia- ischemia, and 3) the watershed penumbra. In addition, we will use noninvasive imaging to track tissue uptake of photoacoustically sensitive dyes conjugated to different size molecules and relate regional differences in size-dependent blood brain-barrier permeability to markers of energy metabolism. Finally, we will investigate whether stabilizing anti-inflammatory, anti-epileptic, anti-platelet, pro-vasodilatory, and pro-angiogenic epoxyeicosatrienoic acids with an inhibitor of soluble epoxide hydrolase (sEH) is protective. Though pretreatment with such inhibitors is protective in adult rodent models of transient cerebral ischemia, post- treatment efficacy has not been determined with prolonged ischemia or in immature brain. We will test the concept that a multi-potent sEH inhibitor will attenuate neuroinflammation, blood-brain barrier permeability, perivascular loss of aquaporin-4 channels, ischemia-induced increase in Sur1-TrpM4 channels known to contribute to malignant edema, and the loss of peri-ischemic neurons, while promoting VEGF expression; we will also determine whether an inhibitor of EET synthesis will exert the opposite effects. Therefore, this application will reveal new insights into the mechanisms of injury from perinatal thrombotic ischemia, provide a potential therapeutic target, and enable an innovative technological advance for screening newborns for stroke.