In Vitro Evaluation of Confounders in Brain Optical Monitoring: A Review.

Area of Science:

• Biomedical Optics
• Neuroscience Instrumentation
• Medical Imaging

Background:

• Non-invasive optical techniques like near-infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS), and photoplethysmography (PPG) offer portable, real-time monitoring of cerebral blood flow (CBF), intracranial pressure (ICP), and oxygenation.
• Accuracy of these optical methods can be compromised by confounding factors such as extracerebral tissue layers, skin pigmentation, skull thickness, and brain pathologies.

Purpose of the Study:

• To review in vitro studies using phantoms to assess the impact of confounders on optical brain monitoring techniques.
• To identify limitations in current research and suggest future directions for improving the reliability of non-invasive cerebral monitoring.

Main Methods:

• Systematic literature search for in vitro studies employing phantoms to simulate human head properties.
• Analysis of studies focusing on extracerebral layers, skin pigmentation, skull thickness, and brain pathologies.

Main Results:

• Extracerebral layers and skull thickness were found to influence measurement accuracy.
• Skin pigmentation introduces bias into optical measurements.
• Pathologies like edema and hematomas affect optical signals, but their impact on parameter estimation requires further investigation.

Conclusions:

• Current phantom models and optical devices have limitations affecting comparability.
• Further research is needed, particularly on improved brain phantoms simulating pulsatile signals for photoplethysmography (PPG) systems.
• Addressing confounder impacts is crucial for enhancing the reliability of optical brain monitoring technologies.