Brain Oxygenation MRI Calibration Using Deoxyhemoglobin Contrast
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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 magnetic susceptibility, then relative deoxygenated hemoglobin concentration can be obtained, but the measurement precision of arterial and venous oxygen saturation is insufficient due to lack of conversion factor
Solution Approach 1:
The patent introduces an intermediary calibration process using a reference voxel (such as the choroid plexus or middle cerebral artery) that provides a known relationship between magnetic susceptibility and oxygen saturation. This intermediary reference measurement enables the derivation of conversion factors that link QSM values to physiological oxygen saturation metrics, thereby resolving the information loss problem.
Solution Approach 2:
The patent employs parameter changes by varying oxygen saturation levels through sequential gas delivery (changing inhaled oxygen concentrations) and measuring the corresponding changes in magnetic susceptibility signals. This dynamic parameter variation allows calibration curves to be established, converting static relative QSM measurements into dynamic absolute oxygen saturation values.
2Measurement precision
If sequential gas delivery is used to impose SaO2 changes, then calibration data can be obtained, but the complexity of the measurement system increases
Solution Approach 1:
The patent applies self-service by utilizing the subject's own respiratory system to deliver the calibration stimulus. The subject breathes gas mixtures with controlled oxygen concentrations through a simple mask interface, and their own circulation and metabolism naturally produce the required SaO2 variations. This eliminates the need for complex external pumps or invasive catheter-based gas delivery systems.
Solution Approach 2:
The sequential gas delivery system serves multiple functions: it acts as both the oxygenation source and the calibration stimulus generator. The same gas delivery mechanism that controls arterial oxygen saturation also provides the varying input signal needed for calibration, eliminating the need for separate calibration devices and reducing overall system complexity.
3Measurement precision
If reference voxel measurements are used for calibration, then conversion to absolute oxygen saturation is enabled, but the difficulty of detecting and measuring appropriate reference regions increases
Solution Approach 1:
The patent utilizes magnetic susceptibility contrast (analogous to color changes in optical imaging) to identify reference voxels. Blood vessels and structures like the choroid plexus exhibit distinct susceptibility signatures that allow automated detection and segmentation. These structures appear with characteristic signal intensities and spatial patterns that facilitate their identification as reference regions without manual intervention.
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 SaO2 and OEF by calibrating MRI measurements to deoxyhemoglobin concentration, providing accurate brain tissue oxygenation measurements.
Implementation Method 1
Quantitative Susceptibility Mapping (QSM) measures magnetic susceptibility in tissues, providing relative strengths and directions of susceptibility
Implementation Method 2
measuring brain tissue oxygenation through BOLD (blood oxygen level-dependent) calibration using deoxyhemoglobin contrast methods
Data Source
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Figure 3A~3C
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.