B1 Magnetic Field Phase Mapping in MRI Systems
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Solution Overview
Problem
Current MRI systems face challenges in accurately determining the phase distribution of the B1+ magnetic field, especially in high magnetic fields (3 Tesla or higher), which affects the uniformity and quality of MR images, as existing methods fail to distinguish between the phases of B1+ and B1− magnetic fields.
Innovation Solution
A system that acquires B1 magnetic field phase information by applying RF pulses to a target object via multiple RF coil elements, distinguishing between B1+ and B1− magnetic fields through echo response signals, and combining this information to provide a B1 map indicating spatial distribution, thereby enhancing B1+ magnetic field uniformity and electrical conductivity imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RF pulses are applied via multiple RF coil elements to improve B1 magnetic field uniformity, then the B1+ magnetic field strength increases, but the ability to distinguish between B1+ and B1- magnetic field phases deteriorates
Solution Approach 1:
The patent segments the B1 magnetic field measurement into two distinct components: B1+ (transmit) and B1- (receive). By acquiring first information from individual coil elements and second information from combined coil elements, the system separately characterizes the transmit and receive magnetic field phases. This segmentation allows precise determination of B1+ phase distribution while accounting for B1- contributions, resolving the measurement accuracy issue.
Solution Approach 2:
The patent introduces an intermediary processing step where the system acquires echo response signals and performs mathematical operations to isolate B1+ phase information. By using the relationship between first information (individual coil phases) and second information (combined coil phases), the system acts as an intermediary to extract pure B1+ phase distribution, enabling accurate measurement despite the presence of both B1+ and B1- fields.
2Manufacturing precision
If B1 shimming is performed using multiple RF coil elements, then MR image quality improves, but the complexity of determining spatial B1 magnetic field distribution increases
Solution Approach 1:
The patent implements a universal B1 mapping method that works across different MRI system configurations. The same approach of acquiring first information from individual coils and second information from combined coils can be applied regardless of the number of RF coil elements or their specific arrangement. This multi-functional approach simplifies the overall system by providing a unified solution for B1 mapping that supports various coil configurations and shimming requirements.
Solution Approach 2:
The system performs self-characterization of the B1 magnetic field by automatically acquiring and processing echo response signals from the target object. The B1 mapping process is self-contained, using the MRI system's own RF coils and signal processing capabilities to determine spatial B1 distribution without requiring external measurement devices or complex additional hardware, thereby reducing overall system complexity.
3Productivity
If phase information of both B1+ and B1- magnetic fields is acquired simultaneously, then data acquisition speed increases, but the precision of B1+ phase determination decreases
Solution Approach 1:
The patent performs preliminary acquisition of first information from individual RF coil elements before combining them to acquire second information. This preliminary characterization of each coil's B1+ and B1- phase contributions allows the system to process the combined signal more effectively. By preparing the individual coil data first, the system can then efficiently extract precise B1+ phase information from the combined measurement, maintaining both acquisition speed and precision.
Solution Approach 2:
The system employs periodic acquisition sequences where RF pulses are applied in a structured manner to different coil element combinations. This periodic action allows the system to cycle through different measurement configurations, acquiring first information and second information in alternating sequences. This approach maintains high data acquisition speed while enabling precise separation and determination of B1+ phase information through the periodic structure of the measurements.
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 allows for precise determination of B1+ magnetic field phase distribution, improving MR image uniformity and enabling effective electrical property tomography, particularly in high magnetic field MRI systems.
Implementation Method 1
A transmission RF magnetic field (B1+ magnetic field) is a magnetic field which induces actual magnetic resonance by rotating a magnetization vector of at least one type of atomic nucleus included in a target object in a main magnetic field direction when RF pulses are applied to the target object via an RF coil
Implementation Method 2
The B1+ magnetic field induces nucleomagnetic resonance with respect to a magnetization vector, thereby laying the magnetization vector on a transverse plane. When a magnetization vector lies on a transverse plane, the magnetization vector rotates on the transverse plane at the Larmor frequency, and the rotation of the magnetization vector induces an electromotive force (EMF) in a reception RF coil
Data Source
AI summary
A system acquires RF magnetic field information (B1 magnetic field information) in response to generated radio frequency (RF) pulses applied to a target object via at least one of a plurality of RF coil elements in a magnetic resonance imaging (MRI) system. The system acquires first information comprising B1 magnetic field phase information of a B1 magnetic field formed by the respective RF coil elements and acquires second information comprising B1 magnetic field phase information of a B1 magnetic field formed by a combination of two or more of a plurality of RF coil elements. The system acquires third information comprising B1 magnetic field phase information by combining the first information and the second information and processes the first, second and third information in providing a B1 map indicating spatial distribution of a B1 magnetic field.