Persistent penumbra in a rabbit stroke model: incidence and histologic characteristics

Dynamic EPR Oximetry of Changes in Intracerebral Oxygen Tension During Induced Thromboembolism

Cerebral tissue oxygenation (oxygen tension, pO₂) is a critical parameter that is closely linked to brain metabolism, function, and pathophysiology. In this work, we have used electron paramagnetic resonance oximetry with a deep-tissue multi-site oxygen-sensing probe, called implantable resonator, to monitor temporal changes in cerebral pO₂ simultaneously at four sites in a rabbit model of ischemic stroke induced by embolic clot. The pO₂ values in healthy brain were not significantly different among the four sites measured over a period of 4 weeks. During exposure to 15% O₂ (hypoxia), a sudden and significant decrease in pO₂ was observed in all four sites. On the other hand, brief exposure to breathing carbogen gas (95% O₂ + 5% CO₂) showed a significant increase in the cerebral pO₂ from baseline value. During ischemic stroke, induced by embolic clot in the left brain, a significant decline in the pO₂ of the left cortex (ischemic core) was observed without any change in the contralateral sites. While the pO₂ in the non-infarct regions returned to baseline at 24-h post-stroke, pO₂ in the infarct core was consistently lower compared to the baseline and other regions of the brain. The results demonstrated that electron paramagnetic resonance oximetry with the implantable resonator can repeatedly and simultaneously report temporal changes in cerebral pO₂ at multiple sites. This oximetry approach can be used to develop interventions to rescue hypoxic/ischemic tissue by modulating cerebral pO₂ during hypoxic and stroke injury.

Phase-change nanoparticles using highly volatile perfluorocarbons: toward a platform for extravascular ultrasound imaging

Recent efforts using perfluorocarbon (PFC) nanoparticles in conjunction with acoustic droplet vaporization has introduced the possibility of expanding the diagnostic and therapeutic capability of ultrasound contrast agents to beyond the vascular space. Our laboratories have developed phase-change nanoparticles (PCNs) from the highly volatile PFCs decafluorobutane (DFB, bp =-2 °C) and octafluoropropane (OFP, bp =-37 °C ) for acoustic droplet vaporization. Studies with commonly used clinical ultrasound scanners have demonstrated the ability to vaporize PCN emulsions with frequencies and mechanical indices that may significantly decrease tissue bioeffects. In addition, these contrast agents can be formulated to be stable at physiological temperatures and the perfluorocarbons can be mixed to modulate the balance between sensitivity to ultrasound and general stability. We herein discuss our recent efforts to develop finely-tuned diagnostic/molecular imaging agents for tissue interrogation. We discuss studies currently under investigation as well as potential diagnostic and therapeutic paradigms that may emerge as a result of formulating PCNs with low boiling point PFCs.