Magnetic Field Map Determination in MR Systems
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Solution Overview
Problem
Current methods for determining magnetic field maps in MR systems with movable patient supports are inefficient, leading to suboptimal homogeneity and increased imaging time due to the inability to separately measure stationary and position-dependent magnetic field components, resulting in limited table movement thresholds and reduced image quality.
Innovation Solution
A method that separates magnetic field components into stationary and position-dependent components using an absolute field map, allowing for the calculation of a magnetic field map at new table positions without remeasurement, thereby extending the table movement threshold and enabling more efficient shim settings and homogenization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If magnetic field map measurement is performed after every table movement, then magnetic field homogeneity is maintained, but examination time increases significantly
Solution Approach 1:
The magnetic field map is segmented into stationary components (independent of table position) and position-dependent components (varying with table position). By separating these components, the system only needs to measure and store the position-dependent variations, allowing rapid calculation of field maps at new positions without complete remeasurement, thus reducing examination time while maintaining homogeneity accuracy.
Solution Approach 2:
The stationary magnetic field components are measured and stored in advance during system calibration. This preliminary measurement eliminates the need to remeasure these invariant components after table movements, allowing the system to quickly compute field maps at new positions using only the pre-stored stationary data combined with measured position-dependent variations.
2Manufacturing precision
If table movement threshold is limited to ensure field map accuracy, then magnetic field homogeneity is maintained, but table positioning flexibility is reduced
Solution Approach 1:
By segmenting the field map into stationary and position-dependent components, the system can accurately predict field conditions at any table position within the homogeneity volume. This eliminates the need for conservative movement thresholds, as the system can calculate precise field maps for any position using the separated components, thereby maximizing table positioning flexibility while maintaining homogeneity.
3Measurement precision
If complete field map remeasurement is performed after table movement, then measurement accuracy is ensured, but adjustment time increases
Solution Approach 1:
The position-dependent component is extracted from the complete field map measurement and stored separately. After table movements, only this extracted position-dependent component needs to be remeasured and combined with the pre-stored stationary components, rather than performing complete field map remeasurement. This extraction approach maintains measurement precision while dramatically reducing adjustment time.
4Manufacturing precision
If shim coil current optimization is performed frequently, then magnetic field homogeneity is improved, but system complexity and processing time increase
Solution Approach 1:
The field map segmentation into stationary and position-dependent components enables the shim optimization process to work with pre-processed, separated data rather than complete field maps. This segmentation simplifies the optimization calculations by eliminating redundant stationary components from repeated computations, reducing processing complexity and time while maintaining the ability to achieve optimal homogeneity at any table position.
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 significantly reduces adjustment time, allows for higher-quality imaging, and enables precise homogenization of the magnetic field over larger volumes without degrading image quality, even with extensive patient support movement.
Implementation Method 1
Magnetic Resonance Imaging (MRI) is based on spins of atomic nuclei aligned in a magnetic B0 field
Implementation Method 2
In order to suppress B0 inhomogeneity caused by the tissue, shim coils, which may be part of a gradient coil, or local shim coils
Data Source
AI summary
A method and system for determining a magnetic field map in a MR system based on position of a movable patient support of the MR system are provided, wherein a first resulting field map including position dependent information about a magnetic field distribution in a homogeneity volume including an examination volume of the MR system is provided when the movable patient support is located at a first position, wherein a stationary field map including information about a magnetic field distribution in the homogeneity volume is provided, which is independent of the position of the movable patient support, wherein a position dependent field map including information about a magnetic field distribution in the homogeneity volume mainly influenced by a position of the movable patient support is determined using the stationary field map and the first resulting field map, and wherein a second resulting field map in the homogeneity volume is determined when the movable patient support is located at a second position different from the first position, using the stationary field map and the position dependent field map.