Numerical Optimisation of a NIRS Device for Monitoring Tissue Oxygen Saturation

Area of Science:

• Biomedical Engineering
• Medical Monitoring Devices
• Tissue Optics

Background:

• Pressure injuries (PI) are a significant risk for mobility-restricted individuals, particularly affecting the sacrum and ischial tuberosity.
• Early detection of tissue oxygen desaturation is crucial for preventing PI development.
• Current monitoring methods may lack the specificity and continuous monitoring capabilities needed for high-risk populations.

Purpose of the Study:

• To develop a wearable, textile-integrated near-infrared spectroscopy (NIRS)-based monitor for tissue oxygen saturation (StO2).
• To alert mobility-restricted individuals, such as paraplegics, to critical tissue oxygen desaturation in PI-prone areas.
• To optimize sensor design for accurate StO2 measurements up to 3 cm depth, considering physiological adipose tissue thickness.

Main Methods:

• Utilized numerical methods including finite element analysis, image reconstruction, stochastic gradient descent with momentum (SGDm), and genetic algorithms.
• Developed a methodology to determine optimal wavelengths and source-detector geometry for StO2 measurement.
• Optimized sensor design for adipose tissue thicknesses (ATT) ranging from 1 mm to 5 mm, using a priori optical properties of skin, fat, and muscle.

Main Results:

• Identified that optimal wavelengths, source-detector geometry, and number of sources/detectors are dependent on ATT and hypoxic region characteristics.
• A genetic algorithm selected four wavelengths, aligning with major tissue chromophores (O2Hb, HHb, H2O, lipid) and literature values.
• Optimized sensor configuration achieved good StO2 reconstruction across varied tissue layer geometries.

Conclusions:

• The developed wearable NIRS monitor shows promise for early detection of tissue hypoxia in at-risk populations.
• The optimized sensor design and methodology enable accurate StO2 monitoring in the presence of varying tissue optical properties and depths.
• This technology could significantly aid in the prevention of pressure injuries among individuals with limited mobility.