RF Coil Shimming for Electric Properties Tomography Null Points
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Solution Overview
Problem
Magnetic resonance systems face challenges in accurately deriving electric permittivity values across the entire field of view due to null points in the electric field, limiting the imaging of complete slices since permittivity is inversely proportional to the z-component of the electric field.
Innovation Solution
A radio frequency coil system with multiple elements generates shifted electric fields by adjusting weight factors for input signals, allowing for the computation of electric permittivity maps from resonance data, ensuring non-zero z-component values across the entire field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single RF coil element is used to generate electric fields for permittivity measurement, then the measurement process is simple, but null points (zero crossings) appear in the field of view causing inaccurate permittivity derivation
Solution Approach 1:
The RF coil system is segmented into multiple coil elements, each generating electric fields with different null point positions. By dividing the measurement task across multiple elements and combining their data, the system eliminates the null point problem while maintaining measurement simplicity.
2Measurement precision
If multiple RF coil elements with different weightings are used to shift zero crossing points, then permittivity can be accurately derived across the entire field of view, but the device complexity and data processing requirements increase
Solution Approach 1:
Multiple electric field measurements from different coil elements are merged through superposition and phase combination. The complex electric fields from N coil elements are combined to eliminate null points across the field of view, achieving complete spatial coverage for permittivity mapping.
Solution Approach 2:
The weighting factors (amplitude and phase parameters) of each coil element are changed to shift the zero crossing points of their electric fields. By adjusting these parameters, the system ensures that null points from different elements occur at different locations, allowing comprehensive coverage when combined.
3Ease of manufacture
If electric permittivity is derived from a single electric field measurement, then the computation is straightforward, but regions with zero z-component of electric field cannot be imaged
Solution Approach 1:
The system performs continuous useful action by acquiring electric field data from multiple coil elements at different weightings. This continuous data collection ensures that every region in the field of view is measured under conditions where the electric field z-component is non-zero, enabling complete and reliable permittivity mapping.
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 accurate derivation of permittivity distribution for the entire field of view, overcoming the limitations of existing systems by shifting zero crossing points of electric fields and reconstructing volumetric data representations.
Implementation Method 1
A radio frequency coil system generates radio frequency excitation pulses in an examination region... N coil elements which generate magnetic and electric fields
Implementation Method 2
A main magnet, typically superconducting, which generates a spatially and temporally constant magnetic field Bo through an examination region
Data Source
AI summary
A radio frequency coil system (34) used in the context of electric properties tomography (EPT, electrical impedance tomography, EIT, applied potential tomography, APT) generates radio frequency excitation pulses in an examination region (14). The radio frequency coil system (34) includes N coil elements (38) which generate magnetic (H) and electric (E) fields. A weight setting device (54) sets weight factors for input signals for the coil elements (38). A transmitting system (52) creates RF pulses, at least two sets of each with differently weighted input signals, and transmits the at least two sets of RF pulses to the coil elements (38) such that each of the transmitted RF pulse sets generates shifted electric fields (110, 112) having a shifted zero crossing point (120, 122) from each other. An image processor (62) computes electric permittivity maps from resonance induced by the at least two sets of RF pulses with different weighting.