Magnetic Resonance Cerebral Oxygen Mapping with Separated R2 and R2′ Signals
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Solution Overview
Problem
Existing methods for measuring cerebral oxygen metabolism, such as PET imaging and qBOLD MRI, are invasive, costly, time-consuming, or suffer from measurement errors due to mutual coupling effects and magnetic field non-uniformity, making precise 3-dimensional measurement of cerebral metabolic rates challenging.
Innovation Solution
A magnetic resonance imaging device and method using multi-echo UTE-AUSFIDE, VS-VSL, and pCASL data acquisition, combined with data pre-processing and quantitative model processing, to separately measure RF-reversible and RF-irreversible transverse relaxation rates, susceptibility, and induced magnetic field offsets, enabling precise 3-dimensional mapping of cerebral blood volume, oxygen extraction fraction, and metabolic rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional qBOLD MRI scheme is used to measure OEF, then non-invasive measurement is achieved, but measurement precision deteriorates due to mutual coupling effect between CBVv and [dHb]v
Solution Approach 1:
The patent segments the transverse relaxation rate constant R2* into two independent components: R2 (spin-spin relaxation) and R2' (susceptibility-related relaxation). By separately measuring and subtracting R2 from R2*, the patent isolates the R2' component that is directly related to deoxygenated hemoglobin, thereby eliminating the mutual coupling effect between CBVv and [dHb]v that plagues conventional qBOLD methods.
Solution Approach 2:
The patent introduces an intermediary variable Yv (venous blood oxygen saturation) as a mediating parameter that connects the measured R2' to the physiological parameters of interest. By using Yv as an intermediary in the calculation chain (R2' → Yv → OEF), the patent creates a more direct and less coupled measurement pathway compared to conventional methods.
2Measurement precision
If PET imaging is used to measure CMRO2, then measurement capability is achieved, but invasiveness and cost increase due to radio tracer insertion
Solution Approach 1:
The patent replaces the expensive and harmful radio tracers used in PET imaging with endogenous hemoglobin molecules that are already present in the body. These hemoglobin molecules serve as natural contrast agents for MRI, eliminating the need for external tracer injection while providing sufficient signal for CMRO2 measurement.
Solution Approach 2:
The patent utilizes the body's own hemoglobin molecules to generate the MRI signal needed for measurement. The deoxygenated hemoglobin naturally creates magnetic susceptibility effects that can be detected by MRI, allowing the system to serve itself without requiring external radioactive tracers or additional contrast agents.
3Ease of operation
If qBOLD method is used to map OEF, then completely non-invasive scheme is achieved, but reproducibility deteriorates due to difficulty in obtaining unique solution from mutual coupling
Solution Approach 1:
The patent segments the measurement process into distinct steps: first measuring R2 using spin echo sequences, then measuring R2* using gradient echo sequences, and finally calculating R2' by subtraction. This segmentation creates a deterministic calculation pathway that eliminates the ill-posed inverse problem and mutual coupling issues that reduce reproducibility in conventional qBOLD methods.
4Object-affected harmful factors
If conventional MRI schemes are used for CMRO2 measurement, then non-invasive alternative to PET is achieved, but imaging time increases due to complex preparation and sequences
Solution Approach 1:
The patent merges the measurement of multiple parameters (R2, R2*', and by extension OEF and CMRO2) into a single integrated MRI protocol. By acquiring both spin echo and gradient echo data in one imaging session and processing them together, the patent reduces the total imaging time compared to performing separate measurements for each parameter.
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 high-resolution, 3-dimensional mapping of cerebral oxygen metabolism with reduced signal distortion, improving image resolution and qBOLD model performance without increasing imaging time, and accurately distinguishing heme and non-heme iron contributions.
Implementation Method 1
qBOLD (quantitative blood oxygen level dependent) MRI (Magnetic Resonance Image) is a representative technology for measuring OEF, and is based on a MRI signal change model under the surrounding magnetic field disturbance effect of deoxygenated hemoglobin (dHb).
Implementation Method 2
a time constant representing the signal change is denoted as R2′, and corresponds to an RF-inversion possible portion of a transverse relaxation rate constant R2*(R2′=R2*−R2)
Data Source
AI summary
A magnetic resonance imaging device for measuring cerebral oxygen metabolism includes a memory configured to store computer-readable instructions and one or more processors configured to execute the instructions such that the one or more processors is configured to acquire UTE (ultrashort echo-time)-AUSFIDE (alternating unbalanced SSFP-FID & SSFP-ECHO) image data, VS-VSL (velocity-selective venous spin labeling) image data, and pCASL (pseudo-continuous arterial spin labeling) image data, process a plurality of preliminary information data for quantitative model processing and process CBF (cerebral blood flow) information data, acquire variable information (Yv) to derive an oxygen extraction fraction (OEF) and a cerebral metabolic rate of oxygen (CMRO2) in order to acquire a 3-dimensional oxygen metabolic rate map of an entire brain, derive the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen (CMRO2) and generate an oxygen metabolic rate map image as a magnetic resonance image.