Reference-Voxel MRI Calibration for Absolute Brain Oxygenation
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Solution Overview
Problem
Current methods for measuring brain oxygenation, such as Quantitative Susceptibility Mapping (QSM), provide only relative measurements of the oxygen extraction fraction (OEF) and lack a conversion factor to determine arterial and venous oxygen saturation, preventing accurate quantification.
Innovation Solution
A method and system that measures magnetic signals in a reference voxel while imposing arterial blood oxygen saturation (SaO2) changes using sequential gas delivery, allowing for the calibration of MRI measurements to deoxyhemoglobin concentration, enabling accurate quantification of SaO2 and OEF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Quantitative Susceptibility Mapping (QSM) is used to measure brain oxygenation, then relative measurements of oxygen extraction fraction (OEF) are provided, but accurate quantification of arterial and venous oxygen saturation cannot be achieved due to lack of conversion factor
Solution Approach 1:
The patent introduces a reference substance (substance with known oxygenation properties) as an intermediary to bridge the gap between QSM measurements and actual oxygen saturation. By measuring the reference substance alongside brain tissue, the system establishes a conversion factor that translates relative QSM values into absolute oxygen saturation measurements, resolving the information loss about the conversion relationship.
Solution Approach 2:
The patent employs changes in oxygenation state (from normoxia to hypoxia) to create measurable differences in magnetic susceptibility. By dynamically altering the oxygenation parameters of the reference substance and brain tissue, the system generates calibration data that enables accurate quantification of oxygen extraction fraction and oxygen saturation through linear regression analysis of the susceptibility changes.
2Measurement precision
If QSM measurements are used, then relative OEF values are obtained, but fractional differences and absolute oxygen extraction fraction cannot be determined
Solution Approach 1:
The reference substance serves as a mediator that provides known oxygenation values to calibrate the QSM measurements. This intermediary allows the system to determine absolute OEF values and fractional differences by comparing the reference substance measurements with brain tissue measurements, thereby obtaining quantitative conversion factors for OEF calculation.
Solution Approach 2:
The system uses the measured oxygenation values from the reference substance as feedback to calibrate the QSM measurements. By continuously comparing the reference substance measurements (with known oxygenation) against the brain tissue measurements, the system iteratively determines the conversion factor and achieves accurate absolute OEF quantification.
3Measurement precision
If blood flow data is integrated with QSM, then some information is provided, but accurate determination of oxygen extraction fraction remains unresolved
Solution Approach 1:
The patent merges the QSM measurement system with a reference substance measurement system into a unified imaging protocol. By combining the magnetic susceptibility measurements of brain tissue with the known oxygenation measurements of the reference substance within the same imaging session, the system achieves accurate OEF determination without requiring separate blood flow measurement systems.
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
Enables precise quantification of brain tissue oxygenation and oxygen extraction fraction (OEF) by calibrating MRI measurements, facilitating consistent measurements across different brain regions and populations, supporting robust clinical and research applications.
Implementation Method 1
Quantitative Susceptibility Mapping (QSM) measures magnetic susceptibility in tissues, providing relative strengths and directions of susceptibility
Implementation Method 2
measuring magnetic signals in a reference voxel while imposing arterial blood oxygen saturation (SaO2) changes... calibration of MRI measurements to deoxyhemoglobin concentration
Data Source
AI summary
The present specification discloses a method for measuring brain tissue oxygenation in a subject. The method comprises the following steps: measuring a magnetic signal in a reference voxel of the subject's brain while imposing a series of arterial oxygen saturation changes using sequential gas delivery; calculating a relationship between the magnetic signal and the arterial oxygen saturation in the reference voxel; measuring a magnetic signal in a target voxel; and calculating the hemoglobin saturation in the target voxel based on the established relationship between the magnetic signal and the SaO2 in the reference voxel. This calibration of magnetic signal for SaO2 enables the conversion of magnetic signal to SaO2 throughout blood-containing voxels throughout the brain.