B1 Mapping in MRI via k-Space Filtering
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Solution Overview
Problem
Current methods for generating multi-dimensional maps of RF magnetic fields in MRI systems are limited by non-uniformity and motion artifacts, leading to inaccurate image reconstruction and prolonged acquisition times, especially at higher field strengths and in moving subjects.
Innovation Solution
The method involves acquiring two-dimensional sets of B1 amplitude-tagged MRI data in the spatial frequency domain, processing k-space data to generate frequency-filtered subsets, transforming these into spatial domain data, and combining them to produce B1 maps using inverse trigonometric functions, allowing for accurate and efficient determination of RF field patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional B1 mapping methods are used, then acquisition is possible, but motion artifacts and non-uniformity reduce measurement precision
Solution Approach 1:
The patent transforms the B1 mapping problem from image space to k-space (spatial frequency domain). By performing frequency domain filtering and analysis in k-space, the method separates the B1 modulation information from motion-induced artifacts more effectively, enabling accurate B1 measurement even in the presence of subject motion during acquisition
Solution Approach 2:
The patent changes the domain parameter from spatial domain to spatial frequency domain (k-space). This parameter transformation allows for selective frequency filtering that isolates the B1 modulation signal from motion artifacts, significantly improving measurement precision without requiring the subject to remain perfectly still during acquisition
2Productivity
If conventional B1 mapping methods are used, then B1 maps can be generated, but acquisition times are prolonged
Solution Approach 1:
The patent extracts only the necessary frequency components related to B1 modulation from the k-space data using targeted frequency filtering. By selectively extracting these specific frequency bands rather than processing the entire frequency spectrum, the method reduces computation time and enables faster B1 map generation while maintaining accuracy
Solution Approach 2:
The patent applies partial action by focusing computational resources only on the specific frequency regions containing B1 modulation information, rather than uniformly processing all frequency components. This selective approach significantly reduces acquisition and processing time while preserving the essential B1 mapping functionality
3Manufacturing precision
If conventional B1 mapping methods are used, then imaging can proceed, but non-uniformity reduces manufacturing precision
Solution Approach 1:
The patent replaces complex physical field uniformization mechanisms with a computational approach in k-space. By using frequency domain filtering and mathematical processing to correct and analyze B1 non-uniformity, the system achieves improved field uniformity measurements without requiring additional hardware complexity or mechanical adjustments
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 reduces errors, achieves faster acquisition times, and provides high-resolution B1 maps with improved accuracy and dynamic range, even in the presence of motion, enhancing image quality and system design.
Implementation Method 1
MRI systems all utilize the principle of nuclear magnetic resonance (NMR) wherein nuclei having a net magnetic moment are immersed in a static background magnetic field B0. Ideally, this background static magnetic field is homogeneous throughout a volume to be imaged
Implementation Method 2
The nuclear magnetic moments can be thought of as rotating about an axis at a frequency which is proportional to the magnetic field imposed upon the nucleus at its particular spatial location. The so-called Larmor angular frequency ω=γβ where γ is a gyromagnetic ratio constant and β is the strength of the imposed magnetic field. By superimposing an auxiliary magnetic field having a linear gradient, the Larmor frequency of nuclei disposed along the changing field gradient will now have different values
Implementation Method 3
By transmitting an RF magnetic field at the Larmor frequency into the volume that is to be imaged, one can selectively excite the nuclear magnetic resonant (NMR) nuclei that happen to fall within a given selected volume so as to nutate the nuclear magnetic moment away from the nominal static magnetic field B0
Implementation Method 4
After such nutation, the nuclear magnetic moment tends to relax back toward nominal alignment with B0, but with characteristic longitudinal and transverse time constants T1, T2 and, in the process, each relaxing nuclear magnetic moment emits a radio frequency response signal that can be detected as an RF signal having a particular amplitude, frequency and phase
Data Source
AI summary
Frequency filtering of spatially modulated or “tagged” MRI data in the spatial frequency k-space domain with subsequent 2DFT to the spatial domain and pixel-by-pixel arithmetic calculations provide robust ratio values that can be subjected to inverse trigonometric functions to derive B1 maps for an MRI system.