Optical Brain Monitoring for Better Stroke Care

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PHILADELPHIA, March 20, 2014 — Advanced technology and simple body positioning could be key in providing acute stroke patients with more effective, individualized treatment in real time.

A team from the University of Pennsylvania has developed a new optical device that can noninvasively and continuously monitor cerebral blood flow (CBF) in stroke patients to gauge how their body positioning could impact blood flow to the brain.

When stroke patients are first admitted to the hospital, they typically are kept flat for 24 hours to increase CBF in the brain regions surrounding the damaged tissue. And while this position does help most stroke patients, the new device has enabled the researchers to discover that, for 29 percent of patients, an elevated rather than flat head position increases CBF and is therefore more beneficial.

Frontal view of cerebral angiography, a commonly used tool in diagnosing strokes and other brain injuries. Now, University of Pennsylvania researchers have developed a new optical device to noninvasively monitor cerebral blood flow activity.

"While, on average, our findings support current guidelines to lay patients flat following stroke, they also suggest that for some stroke patients, lying flat may be either unnecessary or even harmful,” said Dr. John A. Detre, senior author and a professor of neurology and radiology at the university’s Perelman School of Medicine.

The new technology uses a noninvasive probe that is placed on the surface of the patient’s head. It measures fluctuations of NIR light that has traveled through the skull and into the brain, then back out to the tissue surface. These fluctuations, caused by moving red blood cells in tissue, have been shown to accurately track CBF in underlying brain tissue.

Called diffuse correlation spectroscopy (DCS), this new optical technique is more sensitive in detecting CBF changes with body positioning than the traditional transcranial Doppler method, which uses acoustic waves to measure blood flow velocity of the large arteries that supply the brain.

Currently, a stroke patient’s CBF is not often measured. When it is, a single measurement from a CT or MRI scan is taken while the patient is lying flat. The researchers agree that such scans are valuable diagnostic tools, but they historically have not been effective in assessing response to clinical interventions over time.

"Our study suggests that it would be impossible for stroke clinicians to know whether flat [body positioning] is optimal without actually measuring the response," said Dr. Michael Mullen, a Penn stroke neurologist who has been involved in the research. "The ability to measure cerebral blood flow continuously has tremendous potential."

The new optical CBF monitoring device could someday be performed routinely in all patients with acute brain injury, according to the researchers, but further studies are needed.

The work was funded by a Bioengineering Research Partnership grant from the National Institutes of Health's National Institute of Neurological Disorders and Stroke, Center Core in Neuroimaging, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institute of Biomedical Imaging and Bioengineering, and the Sao Paolo Research Foundation and Fundacio Cellex.

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Published: March 2014
Acronym for profile resolution obtained by excitation. In its simplest form, probe involves the overlap of two counter-propagating laser pulses of appropriate wavelength, such that one pulse selectively populates a given excited state of the species of interest while the other measures the increase in absorption due to the increase in the degree of excitation.
AmericasBiophotonicsbrainbrain tissueBrazilcerebral blood flowCT scanImagingMicroscopyMRINational Institute of Biomedical Imaging and BioengineeringNational Institute of Neurological Disorders and StrokeNational Institutes of Healthnear-IR lightneurologyOpticsPennsylvaniaPerelman School of MedicineprobeResearch & TechnologyspectroscopyTCDTest & MeasurementUniversity of Pennsylvaniaacute strokeCBFbody positioningdiffuse correlation spectroscopyDCStranscranial DopplerCenter Core in NeuroimagingSao Paolo Research FoundationFundacio Cellex.

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