B1 Phase Map Correction via Larmor Frequency Mediation
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Solution Overview
Problem
Conventional methods for determining B1 phase maps in magnetic resonance imaging face challenges such as phase ambiguities due to Nyquist phase wrapping, especially at higher B0 fields, leading to inaccuracies and difficulties in designing control sequences, as they rely on reference excitation modes that may not provide sufficient excitation across the entire imaging region.
Innovation Solution
A method that involves acquiring first magnetic resonance data to determine spatially resolved Larmor frequency values and using these to create a correction map, which is then subtracted from raw phase maps to correct for phase errors, ensuring all B1 phase maps are relative to a common reference map, thereby avoiding phase wrapping and improving the quality and reliability of B1 field maps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional reference excitation modes are used to determine B1 phase maps, then the measurement process is simple, but phase ambiguities occur due to Nyquist phase wrapping at higher B0 fields
Solution Approach 1:
The patent introduces a correction map as an intermediary element that mediates between the raw phase maps and the final B1 phase maps. This correction map, derived from Larmor frequency values, acts as a mediator to remove phase wrapping errors without requiring complex measurement procedures, thus resolving the contradiction between measurement simplicity and precision.
Solution Approach 2:
The patent changes the parameter approach by introducing Larmor frequency values as a new parameter to correct phase maps. Instead of directly measuring B1 phase maps with high precision, the method measures Larmor frequency deviations and uses these parameter changes to correct the phase maps, achieving high accuracy while maintaining measurement simplicity.
2Ease of manufacture
If reference excitation modes are used that do not provide sufficient excitation across the entire imaging region, then the measurement process is simpler, but errors are introduced in B1 phase map determination
Solution Approach 1:
The patent implements a feedback mechanism where Larmor frequency values are measured and used to generate correction maps that are applied to the raw phase maps. This feedback loop corrects errors introduced by insufficient excitation in reference modes, ensuring reliable B1 phase map determination while maintaining measurement simplicity.
3Device complexity
If phase wrapping corrections are applied without considering Larmor frequency deviations, then the correction process is simpler, but phase ambiguities remain unresolved
Solution Approach 1:
The patent changes the correction process by introducing Larmor frequency values as a new parameter. Instead of using simple fixed corrections, the method dynamically adjusts corrections based on measured Larmor frequency deviations, resolving phase ambiguities while keeping the correction process manageable in complexity.
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 enhances the quality and reliability of B1 phase maps by accounting for Larmor frequency deviations, reducing errors and ensuring consistent reference across all excitation modes, thus improving the precision of magnetic resonance imaging data.
Implementation Method 1
radio-frequency excitation pulses (also frequently designated as radio-frequency pulses) are emitted via a radio-frequency coil arrangement. The entirety of the radio-frequency pulses (excitation) generates a radio-frequency field that is typically designated as a B1 field, and the spins of resonant excited nuclei are deflected (flipped)
Implementation Method 2
Gradient fields are generated by a gradient coil arrangement while radio-frequency excitation pulses are emitted
Implementation Method 3
A subject to be examined is introduced into a basic magnetic field with a relatively high field strength (known as the B0 field). In order to acquire magnetic resonance data, for example in a slice of the subject, nuclear spins of this slice are excited and the decay of this excitation produces a signal
Data Source
AI summary
In a method to determine a B1 phase map for at least two excitation modes of a radio-frequency coil arrangement of a magnetic resonance apparatus, the radio-frequency coil arrangement having multiple independently controllable transmission channels, and the B1 phase map describing, with spatial resolution, the phase of radio-frequency field this is generated in a respective excitation mode relative to a common reference phase map, first magnetic resonance data describing the phase change of a basic magnetic field of the magnetic resonance apparatus between a first echo time and a second echo time are acquired, and are evaluated to determine a spatially resolved Larmor frequency value that describes the deviation from a nominal Larmor frequency of the magnetic resonance apparatus. To correct raw phase maps derived from second magnetic resonance data acquired using a respective one of the excitation modes, a correction map, determined relative to the reference phase map, is calculated and subtracted from the raw phase map under consideration of the Larmor frequency value and the echo times in the acquisition of the second magnetic resonance data.