Brain Monitoring

The brain is extremely vulnerable to ischemic injury due to its high metabolic demand and reliance on cerebral blood flow for a continuous supply of oxygen and glucose. This vulnerability is well recognized in stroke prevention; however, the risk of ischemic injury extends beyond acute stroke management as it is a primary cause of secondary brain injury in patients with life-threatening neurological emergencies – traumatic brain injury, stroke and cerebral hemorrhage – who require intensive care. Insufficient blood flow to the brain is also a major cause of neonatal brain injury, particularly with preterm infants due to the fragility of immature cerebral vessels. To reduce the incidence of brain injury, the goal of this project is to develop portable optical systems that can be used at the bedside to alert the intensivist team to cerebral ischemia before irreversible tissue damage occurs.

Neonatal Intensive Care

Optical techniques, particular near-infrared spectroscopy (NIRS), have long been considered ideal for brain monitoring in the neonatal intensive care unit (NICU) because the use of light makes this technology extremely safe. Rather than using standard measurements of cerebral blood oxygenation, our research team is focusing on NIRS methods for measuring cerebral blood flow and oxidative metabolism since changes in these parameters are directly linked to the severity of ischemia. In collaboration with colleagues from Neonatology and Neurosurgery, these techniques have been translated to the NICU to investigate pharmaceutical effects on the preterm brain and to detect possible changes in cerebral blood flow caused by hydrocephalus 1.

Neuro Intensive Care

The challenge to adapting optical techniques to adult patients is correcting for the effects of light absorption in scalp and skull as these can lead to substantial errors in cerebral measurements. To meet this challenge, we have developed a depth-sensitive contrast-enhanced NIRS technique that has been validated in an animal model of cerebral ischemia 2. We have also combined this NIRS approach with another emerging optical technique, diffuse correlation spectroscopy, to provide continuous measurements of cerebral blood flow and oxidative metabolism 3.

The optics program will continue to focus on expanding the capabilities of these techniques to provide neuro-monitoring during the first few hours after birth (a time when the preterm brain is vulnerable to injury), to assess blood-brain barrier integrity 4 (a major cause of cerebral edema in critical-care patients), and to detect focal injury by mapping regional cerebral hemodynamics.

1.        Arora, R. et al. Preservation of the metabolic rate of oxygen in preterm infants during indomethacin therapy for closure of the ductus arteriosus. Pediatr. Res. 73, 713–8 (2013).

2.        Elliott, J. T., Diop, M., Lee, T.-Y. & Lawrence, K. S. Model-independent dynamic constraint to improve the optical reconstruction of regional kinetic parameters. Opt. Lett. 37, 2571–3 (2012).

3.        Verdecchia, K., Diop, M., Lee, T.-Y. & St Lawrence, K. Quantifying the cerebral metabolic rate of oxygen by combining diffuse correlation spectroscopy and time-resolved near-infrared spectroscopy. J. Biomed. Opt. 18, 27007 (2013).

4.        St Lawrence, K. et al. Kinetic model optimization for characterizing tumour physiology by dynamic contrast-enhanced near-infrared spectroscopy. Phys. Med. Biol. 58, 1591–604 (2013). 

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K. Verdecchia, a Ph.D. candidate in Medical Biophysics, standing beside an optical system that he helped develop. The system is a combination of time-resolved NIRS and diffuse correlation spectroscopy and is designed to provide continuous measurements of cerebral blood flow and oxidative metabolism
Researchers
K. St. Lawrence
NIRS, functional MRI, mathematical modelling
T.-Y. Lee
medical physics, CT, nuclear medicine, mathematical modelling
M. Diop
biomedical optics
J.J.L. Carson
Imaging Scientist



Technologies
Near-Infrared Spectroscopy
Optical Imaging

Collaborators


Future Directions
Key Accomplishments

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