Multi-Echo B0 Field Deviation Mapping for MRI Shimming
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Solution Overview
Problem
Current magnetic resonance tomography systems face limitations in generating accurate parameter maps for shimming and determining operating frequencies due to phase wraps caused by off-resonances, especially when dealing with multiple spectral components in examination tissues, which restricts the resolution and accuracy of B0 field adjustments.
Innovation Solution
A method involving the acquisition of at least three echo signals with specific echo time differences to generate a parameter map that allows for increased frequency range resolution without the need for separate frequency adjustments, enabling spatially resolved field deviation mapping and dynamic shimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional two-echo methods are used to generate B0 maps, then the measurement process is simplified, but the frequency range resolution is limited due to phase wraps caused by off-resonances
Solution Approach 1:
The measurement process is segmented into multiple echo acquisitions with specific echo time differences. By dividing the frequency range measurement into segments covered by different echo time differences, the patent achieves extended frequency range resolution while avoiding phase wraps that limit conventional two-echo methods
Solution Approach 2:
The patent transitions from a single echo time difference measurement to multiple echo time differences, adding a temporal dimension to the measurement. This dimensional expansion enables the system to resolve frequencies beyond the limited range of conventional methods by utilizing the phase evolution information across multiple time points
2Measurement precision
If separate frequency adjustments are performed, then accurate operating frequency determination is achieved, but the measurement time increases
Solution Approach 1:
The patent merges the B0 map generation process with the operating frequency determination into a single integrated measurement sequence. By combining these two functions that were previously performed separately, the system achieves accurate frequency determination without requiring additional measurement time
Solution Approach 2:
The multi-echo measurement sequence serves multiple functions simultaneously: it generates the B0 map for shimming and determines the operating frequency for the RF system. This multi-functional approach eliminates the need for separate frequency adjustment measurements while maintaining accuracy
3Stability of the object's composition
If in-vivo shimming is performed patient-specifically, then field homogeneity is improved, but the process requires separate B0 map measurement and shim current calculation steps
Solution Approach 1:
The patent combines B0 map measurement and shim current calculation into an integrated workflow. The parameter map generated from multi-echo data directly provides the information needed for both B0 field characterization and subsequent shim current determination, streamlining the in-vivo shimming process
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 resolution of B0 field deviations by an integral factor, allowing for more precise shimming and frequency determination, reducing the need for repeated measurements and enabling slice-specific adjustments, thus improving diagnostic image quality and efficiency.
Implementation Method 1
nuclear spins of specific nuclei that are resonantly excited (i.e. at the Larmor-frequency present at the respective location) by this radio-frequency field
Implementation Method 2
The magnetic resonance frequency (Larmor frequency) applicable at the respective location is directly proportional to the total magnetic field (known as the B0 field)
Implementation Method 3
In addition to the basic field a magnetic field gradient is applied by a gradient system
Implementation Method 4
Radio-frequency excitation signals (RF pulses) are then emitted by a radio-frequency transmitting system
Implementation Method 5
When the excited nuclear spins are relaxed, radio-frequency signals, known as magnetic resonance signals, are resonantly emitted, and these are received by suitable receiving antennae
Data Source
AI summary
In a method and a controller for generating a parameter map for a target volume in an examination object, that represents a field deviation from the resonance frequency of a first spectral component of tissue of object in a magnetic resonance tomography scanner, a spatial region of the object, which includes at least the target volume, is excited. At least three echo signals are formed, wherein a first echo time difference between two the echo signals is chosen such that the phase evolutions of the signals of a second spectral component of the tissue differ, during the first echo time difference, from the first spectral component substantially by 2π, and an echo time of at least a further one of the echo signals is chosen such that it lies between the echo times of the two echo signals having the first echo time difference. Raw data are then acquired from the three echo signals, and the parameter map is then generated therefrom.