RF Shimming Interpolation for MRI B1 Uniformity
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Solution Overview
Problem
High magnetic field MRI systems face challenges in achieving uniform image quality due to non-uniformity of the rotating magnetic field (B1) distribution, which requires extensive measurement and calculation of RF shimming parameters for each imaging section, leading to increased imaging time.
Innovation Solution
Calculating the optimal amplitude and phase of RF for RF shimming using B1 distributions from a predetermined number of sections along a specific axis direction, allowing interpolation for arbitrary imaging sections to minimize the extension of imaging time while maximizing B1 non-uniformity reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If RF shimming parameters are calculated for each imaging section to reduce B1 non-uniformity, then image quality is improved, but imaging time is extended
Solution Approach 1:
The patent performs B1 distribution measurements and RF shimming parameter calculations for a predetermined number of reference sections before actual image acquisition. These pre-calculated parameters are then reused for arbitrary imaging sections through interpolation, avoiding the need to calculate parameters for every single imaging section and thus reducing total imaging time while maintaining B1 uniformity
Solution Approach 2:
The patent creates a B1 distribution map from measurements on a predetermined number of sections and uses this map as a reference for calculating RF shimming parameters for arbitrary imaging sections. This copying approach allows parameter reuse across multiple sections without repeating full measurement and calculation procedures for each section
2Measurement precision
If B1 distribution is measured for all imaging sections, then RF shimming accuracy is maximized, but measurement time increases significantly
Solution Approach 1:
The patent measures B1 distribution for only a predetermined number of sections (e.g., 3 sections) rather than all imaging sections. This partial measurement approach is sufficient to create an accurate enough B1 distribution map for effective RF shimming parameter calculation for arbitrary sections, significantly reducing measurement time while maintaining adequate precision
Solution Approach 2:
The B1 distribution measurements are performed in advance for reference sections before actual image acquisition. These preliminary measurements create a B1 distribution map that can be used for calculating RF shimming parameters for all subsequent imaging sections, avoiding the need for repeated measurements
3Manufacturing precision
If multiple RF channels are used with different phases and amplitudes, then B1 non-uniformity is reduced, but system complexity increases
Solution Approach 1:
The patent adjusts the phases and amplitudes of RF signals for each channel based on pre-calculated RF shimming parameters derived from B1 distribution measurements. By optimizing these parameters (phase and amplitude) for each channel, the system achieves uniform B1 distribution across the imaging region while using the existing multi-channel RF transmission infrastructure
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 effectively reduces B1 non-uniformity across all imaging sections with minimal extension of imaging time, resulting in improved image quality without the need for extensive parameter calculation for each section.
Implementation Method 1
induce magnetic resonance of atomic nuclei in an arbitrary cross section of a test subject to generate magnetic resonance signals
Implementation Method 2
transmit a radio frequency wave (henceforth also referred to as high frequency wave or RF), a kind of electromagnetic waves, to the test subject to excite spins of the atomic nuclei
Implementation Method 3
rotating magnetic field (henceforth referred to as B 1 ), which induces the magnetic resonance phenomenon
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
With minimizing extension of imaging time, the B1 non-uniformity reducing effect of RF shimming is maximized for an imaging section of an arbitrary axis direction and an arbitrary position. B1 distributions are measured for only several sections of one predetermined direction, and a radio frequency magnetic field condition that maximizes the B1 non-uniformity reducing effect for an imaging section of an arbitrary direction and an arbitrary position is calculated from the B1 distribution data. For example, after B1 distributions of only several sections of the AX direction are measured, the optimal radio frequency magnetic field condition for an imaging section of an arbitrary position for the AX direction is obtained by interpolation with optimal radio frequency magnetic field conditions calculated from B1 distributions of two sections near the imaging section, and the optimal radio frequency magnetic field condition for an imaging section of an arbitrary position for the SAG or COR direction is obtained by using only B1 values of a crossing region with the imaging section extracted from the B1 distributions.