Current medical equipment used in clinics does not allow for continuous measuring of brain activity in critically ill patients, and is also expensive. This may change, though, as researchers at the Nałęcz Institute of Biocybernetics and Biomedical Engineering of the Polish Academy of Sciences (IBBE PAS; Warsaw, Poland) are developing a near-infrared (NIR) spectroscopy instrument that enables assessment of brain perfusion (cerebral blood flow to the brain) with light.
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Optical methods for brain monitoring make use of the fact that skull bones are to some extent transparent for light, particularly in the NIR range (between 650 and 850 nm). The properties of hemoglobin are of essential importance, especially the fact that oxygenated hemoglobin interacts with light differently than the reduced form. The phenomenon allows for estimating the degree of oxygenation in the observed region of the body by analyzing the intensity of light penetrating the tissue.
“The volume penetrated by light inside the skull resembles a banana in shape, with one end at the light source and the other at the detector. At the place where the depth of photon penetration in the skull is at its maximum, we reach the cerebral cortex. This means that a fraction of recorded photons has interacted with hemoglobin from the blood circulating in blood vessels of the external layers of the brain,” explains Prof. Adam Liebert, PhD, DSc, who leads the Laboratory for Molecular Imaging at IBIB and is leading the work.
The light source in the NIR spectroscopy instrument from IBBE PAS emits many picosecond light pulses, and the measurements are noninvasive. The measurement requires only that a cap with fixed optical fibers is placed on the patient’s head and the patient is injected with a small dose of a contrast agent (indocyanine green). The examination lasts for a few minutes, and can be repeatedly carried out during the day. What’s more, the instrument is mobile and can be used at the bedside, even in critically ill patients treated in an intensive care unit environment. It can also be used in an operating room.
In collaboration with the Medical University of Warsaw and the Praski Hospital Department of Intensive Care, the IBBE PAS researchers recently carried out optical measurements of brain perfusion in patients with post-traumatic brain injuries. Patients with cerebral edema and subcortical hematoma were included in the study. In both cases, differences with respect to signals collected in healthy volunteers have been observed.
Wojciech Weigl, an anesthesiologist of the Medical University of Warsaw’s Department of Anesthesiology and Intensive Care, coordinated the clinical studies. Further studies are needed before the NIR spectroscopy instrument can be used in hospitals and clinics.