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Thesis Format

Integrated Article


Master of Science


Medical Biophysics


Diop, Mamadou

2nd Supervisor

St. Lawrence, Keith

Joint Supervisor


Neuromonitoring during surgery is used to detect early indications of cerebral injury before permanent damage occurs. A commonly used technology is cerebral oximetry; however, current systems only monitor one brain region and have limited depth sensitivity. A newly developed NIRS system, Kernel Flow, offers the possibility to address both limitations by providing full-head coverage and time-resolved detection to enhance sensitivity to the brain. This work aimed to assess Kernel Flow’s sensitivity to regional cerebral oxygenation changes. Two experiments were conducted. In the first, decreases in cerebral oxygenation caused by transient carotid compression were measured in healthy volunteers. The second was a clinical feasibility study in which the device was used to detect possible regional differences in cerebral desaturation in patients undergoing shoulder surgery. Overall, Kernel Flow showed good sensitivity to regional changes in cerebral oxygenation – although hair provided a practical challenge – and has promise as an intraoperative neuromonitor.

Summary for Lay Audience

A decrease in brain oxygen levels (cerebral desaturation) during surgery can lead to significant post-operative complications, including cognitive decline, longer hospital stays, as well as increased risk of death. Many of these desaturation events are reversible through simple means such as adjusting the head position or administering different drugs. It is, therefore, important to have a safe, non-invasive, bedside brain monitor that would allow clinicians to detect these decreases early to guide subsequent interventions.

Cerebral oximeters, based on principles of near-infrared spectroscopy (NIRS), are commonly used in high-risk surgeries. NIRS is a non-invasive, safe, and portable brain monitoring modality that can measure tissue oxygenation. NIRS relies on the changes in the signal as light travels through tissue. Current devices, however, only monitor one brain region and struggle with providing consistent sensitivity to the brain as the light travels through the scalp and skull. A potential solution is a newly developed device, Kernel Flow, that provides full-head coverage and uses time-resolved detection. Time-resolved technology allows us to differentiate signals from the shallow tissue (scalp and skull) from the deeper tissue (brain). As light travels deeper through tissue, it returns to the detectors later. Time-resolved technology allows us to differentiate whether light arrived early (scalp and skull) or late (brain) to the detector.

Since the Kernel Flow is a new device, little work assessing its capabilities has been performed. The purpose of this study was to assess the sensitivity of the device to regional changes in cerebral oxygenation. First, carotid compression was applied to healthy volunteers to induce decreases in cerebral oxygenation throughout one side of the head. Second, a pilot study was performed on patients undergoing shoulder surgery with the aim of evaluating the ability of the device to detect potential changes in regional cerebral desaturation due to the administration of a drug called phenylephrine, which increases blood pressure.

In conclusion, the device showed good sensitivity to regional changes in cerebral oxygenation (particularly in those with decreased hair density) and tracked the expected oxygenation changes at various depths from the scalp. Overall, Kernel Flow shows promise as an intraoperative neuromonitor.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.