MR Imaging RF Shimming via Receive Profile Mapping
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Solution Overview
Problem
Current MR imaging techniques require lengthy pre-scans for B1-mapping, which is time-consuming and impractical for clinical applications due to the need for sequential determination of transmit sensitivity profiles for each RF antenna.
Innovation Solution
The method involves determining spatial receive sensitivity profiles collectively in a single mapping scan, using these profiles to approximate and derive spatial transmit sensitivity profiles, thereby reducing the time required for B1-mapping and enabling faster RF shimming by controlling the phases and amplitudes of RF feeding in an array of RF antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sequential determination of transmit sensitivity profiles for each RF antenna is performed, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent combines the determination of transmit sensitivity profiles for multiple RF antennas into a single mapping scan by using receive sensitivity profiles from all antennas simultaneously. This merging approach eliminates the need for sequential measurements, reducing pre-scan time from minutes to seconds while maintaining the accuracy needed for RF shimming.
Solution Approach 2:
The patent uses receive sensitivity profiles (traditionally used for image reconstruction) to also determine transmit sensitivity profiles (needed for RF shimming). This multi-functional use of a single measurement dataset allows the system to achieve both receive sensitivity mapping and transmit sensitivity profiling without requiring separate dedicated measurements for each function.
2Stability of the object's composition
If array of RF antennas is used for RF shimming, then homogeneity of RF field is improved, but device complexity increases
Solution Approach 1:
The patent uses receive sensitivity profiles as a copy or surrogate for transmit sensitivity profiles. Since receive and transmit sensitivity profiles are related through the reciprocity theorem, the system can derive transmit information from receive measurements, avoiding the need for complex sequential transmit profiling while maintaining RF shimming effectiveness.
Solution Approach 2:
The system uses the same RF antenna array to perform both transmission and reception functions. The receive sensitivity profiles, naturally acquired during imaging, are repurposed to guide the transmit shimming process, allowing the system to self-characterize without requiring additional dedicated calibration hardware or procedures.
3Productivity
If single mapping scan is used to determine receive sensitivity profiles, then productivity is improved, but measurement precision may be compromised
Solution Approach 1:
The patent performs receive sensitivity profiling as a preliminary action during the main imaging sequence using the same RF pulses and data acquisition. By integrating the sensitivity measurement into the routine imaging workflow rather than requiring a separate dedicated scan, the system achieves both high productivity and sufficient precision for clinical RF shimming applications.
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
This approach significantly shortens the pre-scan time for B1-mapping, allowing for more efficient RF shimming and improving the homogeneity of the RF field without increasing the time proportionally with the number of RF antennas, thus enhancing the practicality of MR imaging.
Implementation Method 1
The magnetic field produces different energy levels for the individual nuclear spins in dependence on the magnetic field strength which can be excited (spin resonance) by application of an electromagnetic alternating field (RF field) of defined frequency (so-called Larmor frequency, or MR frequency)
Implementation Method 2
the magnetization performs a precessional motion about the z-axis. The precessional motion describes a surface of a cone whose angle of aperture is referred to as flip angle
Implementation Method 3
the magnetization in the z direction is built up again with a first time constant T1 (spin lattice or longitudinal relaxation time)
Implementation Method 4
the magnetization in the direction perpendicular to the z direction relaxes with a second time constant T2 (spin-spin or transverse relaxation time)
Implementation Method 5
linear magnetic field gradients extending along the three main axes are superposed on the uniform magnetic field, leading to a linear spatial dependency of the spin resonance frequency
Data Source
AI summary
The invention relates to a magnetic resonance imaging apparatus including an array of two or more RF antennas for transmitting RF pulses to and receiving MR signals from a subject positioned in an examination volume, and where the RF antennas have spatial transmit and receive sensitivity profiles. The apparatus is configured to control the temporal succession, the phase, and the amplitude of the RF feeding of each individual RF antenna. The apparatus is also configured to determine the phases and amplitudes from the spatial transmit sensitivity profiles of the RF antennas, and reconstruct a MR image from a combination of the received MR signals received via the individual RF antennas and from the spatial receive sensitivity profiles of the RF antennas. Further, the apparatus is configured to determine the spatial transmit sensitivity profiles of the RF antennas from the spatial receive sensitivity profiles of the RF antennas, or vice versa.