NIRS Sensor Assembly with Dual Detectors for Cerebral Oximetry
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Solution Overview
Problem
Existing NIRS sensors face limitations in interrogating a substantial amount of tissue while accounting for extracerebral tissue attenuation and minimizing optical shunt effects, leading to suboptimal signal quality and limited information retrieval.
Innovation Solution
A NIRS sensor assembly with a light source and two detectors, where the near detector is positioned outside the optical shunt field and the far detector is aligned linearly with the light source and near detector, with a greater separation distance to increase tissue interrogation and improve signal-to-noise ratio, and a rotatably mounted light source for enhanced flexibility and application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the light source and detector are positioned close together to minimize optical shunt effects, then signal contamination is reduced, but the amount of tissue interrogated is limited
Solution Approach 1:
The patent divides the detection function into two separate detectors: a near detector positioned close to the light source to minimize optical shunt effects, and a far detector positioned at a greater distance to interrogate a larger volume of tissue. Each detector processes signals from different path lengths, allowing the system to segment the measurement into complementary components that together provide both high signal quality and extensive tissue coverage.
Solution Approach 2:
The patent extends the measurement from a single detector position to multiple detector positions at different distances from the light source. This dimensional expansion along the detection path allows simultaneous acquisition of signals with different penetration depths, effectively adding a spatial dimension to the measurement that resolves the contradiction between signal quality and tissue interrogation area.
2Loss of information
If the detector is positioned far from the light source to increase tissue interrogation, then more tissue information is obtained, but optical shunt effects increase signal contamination
Solution Approach 1:
The patent segments the detection function across two detectors at different distances, allowing the near detector to provide clean signals with minimal shunt contamination while the far detector captures signals from deeper tissue. The segmentation enables each detector to optimize for its specific distance, reducing the compromise between information retrieval and contamination.
Solution Approach 2:
The near detector acts as an intermediary measurement that captures the optical shunt component. By measuring the shunt signal separately at the near detector, the system can identify and compensate for its contribution to the far detector signal, effectively using the intermediary measurement to correct for the harmful effect in the primary measurement.
3Device complexity
If a single detector is used to simplify the device, then device complexity is reduced, but the ability to distinguish extracerebral from cerebral attenuation is compromised
Solution Approach 1:
The patent uses two detectors segmented by distance to differentiate between extracerebral and cerebral tissue attenuation. The near detector primarily measures attenuation through extracerebral tissue, while the far detector measures combined attenuation. This segmentation enables the system to mathematically separate the contributions of different tissue types, providing precise differentiation without requiring complex additional components.
Solution Approach 2:
The patent employs a partial measurement approach where the near detector captures a portion of the optical path (extracerebral tissue) and the far detector captures the full path (extracerebral plus cerebral tissue). By measuring partial paths separately, the system can derive complete information through calculation, achieving precise attenuation differentiation with relatively simple detector additions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for improved interrogation of brain tissue, enhancing the signal-to-noise ratio and increasing the amount of targeted tissue interrogated, while reducing signal contamination from the optical shunt field, thereby providing more accurate and reliable cerebral oxygenation monitoring.
Implementation Method 1
light in the near-infrared range (700 nm to 1,000 nm) can pass easily through skin, bone and other tissues
Implementation Method 2
A light signal traveling within any biological medium (e.g., tissue, fluid, etc.) will attenuate, and the amount of attenuation is a function of the medium
Implementation Method 3
Hemoglobin exposed to light in the near-infrared range has specific absorption spectra that varies depending on its oxidation state; i.e., oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) each act as a distinct chromophore
Implementation Method 4
The light signal will also be contaminated by an optical shunt field that surrounds the light source and provides a light path through tissue (usually laterally through the skin surface) without absorption by chromophores such as hemoglobin in blood
Data Source
AI summary
A near infrared spectrophotometric (NIRS) sensor assembly for non-invasive monitoring of blood oxygenation levels in a subject's body is provided that includes a pad, at least one light source, a near light detector, a far light detector, and a cover. The light source is operative to emit near infrared light signals of a plurality of different wavelengths. The near light detector is separated from the light source by a first distance that is great enough to position the first light detector outside of an optical shunt field extending out from the light source. The far light detector is substantially linearly aligned with the near light detector and light source, and is separated from the near light detector by a second distance, wherein the second distance is greater than the first distance.