MRI B1+ Field Estimation for Non-Invasive Tissue Conductivity
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Solution Overview
Problem
Current methods for determining tissue electrical properties, such as conductivity and permittivity, using Magnetic Resonance Imaging (MRI) require invasive electrodes and significant computational resources, and often lack necessary sensitivity data, making them inefficient and uncomfortable for patients.
Innovation Solution
A method and system that estimate tissue electrical properties by generating MRI B1+ maps to determine the magnitude and phase of the B1+ field, combining these to create a complex B1+ field estimate, and solving difference equations to calculate conductivity and permittivity without requiring receiver sensitivity or z-component data, allowing for non-invasive and efficient estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Electrical Impedance Tomography (EIT) with electrodes is used to estimate tissue electrical properties, then conductivity and permittivity can be determined, but patient comfort deteriorates due to invasive electrodes and processing time increases due to significant computational resources needed to solve the inverse problem
Solution Approach 1:
The patent replaces the mechanical/electrical contact system of EIT electrodes with a non-invasive MRI-based measurement system. Instead of using surface electrodes to apply currents and measure voltages, the system uses MRI's electromagnetic fields (B1+ transmit field and B1- receive field) to indirectly measure tissue electrical properties through their effect on the magnetic resonance signal, eliminating the need for physical electrode contact with the patient's body
Solution Approach 2:
The patent introduces MRI signal measurements as an intermediary between the measurement process and tissue electrical properties. Rather than directly measuring electrical properties through electrode contact, the system measures the effect of electrical properties on MRI field distributions (B1+ magnitude and phase, B1- sensitivity), then uses these intermediate measurements to infer the electrical properties through calculated relationships
2Measurement precision
If Electrical Impedance Tomography (EIT) is used to estimate tissue electrical properties, then conductivity and permittivity can be determined, but processing time increases due to significant computational resources needed to solve the inverse problem
Solution Approach 1:
The patent extracts and utilizes specific measurable quantities from the MRI system (B1+ field magnitude and phase, B1- receiver sensitivity) that have direct mathematical relationships with tissue electrical properties. By focusing on these extracted parameters rather than solving the full inverse problem from electrode measurements, the system obtains electrical property estimates through more direct calculations that require less computational resources and time
Solution Approach 2:
The patent creates a simplified model system where MRI field measurements serve as proxies for direct electrical measurements. Instead of solving the complex inverse problem of EIT, the system uses the copied/measured MRI field distributions (which are already available from the imaging process) to infer electrical properties through pre-established mathematical relationships, reducing computational complexity
3Loss of information
If known MRI methods using B1+ maps are used to estimate tissue electrical properties, then some electrical property information can be obtained, but the measurement is incomplete because receiver sensitivity (B1−) and z-component of RF magnetic field (Hz) are not typically available
Solution Approach 1:
The patent makes the MRI system's receive coils perform multiple functions: they continue to detect the standard MRI signal for imaging while simultaneously measuring the B1- receiver sensitivity field distribution. This dual-use approach allows the system to obtain additional information (B1- maps) without adding separate measurement hardware or significantly increasing system complexity, as the same receive coils are used for both imaging and electrical property measurement
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 non-invasive, real-time estimation of tissue conductivity and permittivity within clinically acceptable time frames, providing diagnostically relevant information for identifying tissue abnormalities and evaluating RF safety and therapeutic methods.
Implementation Method 1
MRI or Nuclear Magnetic Resonance (NMR) imaging generally provides for the spatial discrimination of resonant interactions between Radio Frequency (RF) waves and nuclei in a magnetic field
Implementation Method 2
When excited by an RF wave, the spins precess about the main magnetic field at a characteristic Larmor frequency
Implementation Method 3
generating Magnetic Resonance Imaging (MRI) B1+ maps to determine a magnitude of an MRI B1+ field applied to a subject using a plurality of Bloch-Siegert phase shift images
Data Source
AI summary
A system and method for determining electrical properties using Magnetic Resonance Imaging (MRI) are provided. One method includes determining a magnitude of an MRI B1+ field applied to an object, determining a phase of the MRI B1+ field applied to the object and combining the determined magnitude and phase to determine a complex B1+ field estimate. The method further includes estimating one or more electrical properties of the object using the complex B1+ field estimate by directly solving at least one difference equation.