B0 Map Computation for MRI Shim Calibration
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Solution Overview
Problem
Current magnetic resonance imaging (MRI) techniques require lengthy calibration processes to determine the B0 map, which is essential for optimizing the magnetic field homogeneity, leading to increased examination time and reduced patient comfort.
Innovation Solution
A method for computing a final B0 map by simulating and estimating the magnetic field distribution using a trained function, based on the original magnetic field distribution, allowing for the determination of shim currents and reducing the need for additional measurements, thereby shortening the examination time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a series of calibration measurements are performed to determine the B0 map after shimming, then the magnetic field homogeneity is optimized and imaging quality is improved, but the examination time is significantly increased
Solution Approach 1:
The patent applies preliminary action by computing the final B0 map from the original B0 map before the actual shimming measurement is performed. The system calculates what the B0 map would be after shimming based on the measured original B0 map and the determined shim currents, eliminating the need to perform time-consuming calibration measurements after shimming while still providing accurate B0 information for image correction
Solution Approach 2:
The patent creates a computational copy of the final B0 map by simulating the effect of shim currents on the original B0 map. Instead of measuring the actual final B0 map after shimming, the system generates a calculated copy that represents the expected final state, which is then used for image correction purposes
2Measurement precision
If multiple calibration measurements are conducted to account for receive-coil profile dependencies, then the measurement accuracy is improved, but the calibration duration is extended to over a minute
Solution Approach 1:
The system performs preliminary computation of the final B0 map using the original B0 map and predetermined shim currents. This preliminary calculation provides sufficiently accurate B0 information for clinical use without requiring multiple sequential calibration measurements, thereby reducing calibration duration while maintaining acceptable measurement precision
Solution Approach 2:
The patent changes the approach from direct measurement to computational estimation. By transforming the problem from measuring the final B0 map to calculating it from known parameters (original B0 map and shim currents), the system achieves the required precision with significantly reduced time investment
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 enables faster and more efficient MRI examinations by eliminating the need for time-consuming B0 map measurements after shim state adjustment, improving patient comfort and examination efficiency while maintaining high homogeneity of the magnetic field.
Implementation Method 1
This triggers spatially encoded magnetic resonance signals in the patient
Implementation Method 2
gradient pulses for producing magnetic field gradients
Implementation Method 3
radiofrequency (RF) pulses for producing an RF field (also referred to as a B1 field)
Data Source
AI summary
A method for determining a B0 map for, for example, performing an imaging magnetic resonance measurement using a magnetic resonance apparatus, includes measuring an original magnetic field distribution in a measurement volume of the magnetic resonance apparatus, and computing a final B0 map that describes a magnetic field distribution produced in the measurement volume of the magnetic resonance apparatus by setting a shim state. The magnetic field distribution produced in the measurement volume of the magnetic resonance apparatus by setting the shim state differs from the original magnetic field distribution.