Dynamic Shim Parameter Sets for MRI Field Homogeneity
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Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) systems face challenges in achieving homogeneous magnetic fields, particularly when imaging objects with inhomogeneous materials, leading to suboptimal image quality due to limitations in dynamic shimming techniques, which struggle to rapidly adjust shim channels of higher order, resulting in incomplete compensation of local field distortions and signal losses.
Innovation Solution
The method involves dividing the examination region into multiple sections, generating specific shim parameter sets for each section, and dynamically adjusting shim channels to compensate for magnetic field inhomogeneities, allowing for improved homogenization of the magnetic field during data acquisition using multiple shim parameter sets and a B0 field map for enhanced image reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dynamic shimming is used to rapidly adjust shim currents during MRI data acquisition, then the ability to compensate for local field distortions is improved, but the settling time of higher order shim channels becomes insufficient, resulting in incomplete compensation
Solution Approach 1:
The examination region is divided into multiple sections, and separate shim parameter sets are determined for each section. This segmentation allows the system to optimize shimming for smaller regions where field distortions are more uniform, reducing the required settling time while maintaining compensation effectiveness.
Solution Approach 2:
The system dynamically switches between different shim parameter sets corresponding to different sections during data acquisition. By adapting the shim parameters to the currently imaged section rather than using a single global set, the system achieves effective local field compensation with faster settling times.
2Ease of operation
If a single global shim parameter set is used for the entire examination region, then the device operation is simplified, but local field distortions in different sections are not adequately compensated, leading to signal losses
Solution Approach 1:
Instead of applying a uniform shim parameter set globally, the system determines and applies section-specific shim parameter sets. This allows each section to receive optimized compensation tailored to its local field characteristics, improving compensation reliability while maintaining automated operation.
Solution Approach 2:
The system automatically determines multiple section-specific shim parameter sets and switches between them during acquisition without requiring manual intervention. The automated management of multiple parameter sets eliminates the need for complex manual shimming while achieving superior local field compensation.
3Manufacturing precision
If shim channels of higher order are used to compensate for complex field inhomogeneities, then the manufacturing precision of field homogeneity is improved, but the adjustment speed of these channels is reduced, preventing rapid dynamic shimming
Solution Approach 1:
By dividing the examination region into smaller sections, the system can use higher order shim channels for each section with reduced settling time requirements. The smaller spatial extent of each section allows these channels to reach steady state faster while still achieving the necessary field homogeneity precision.
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 signal losses and distortions, improves image quality by allowing for section-specific adjustments of shim currents and frequencies, and reduces variations in image data between sections, resulting in more accurate and natural anatomical representations.
Implementation Method 1
Multiple shim parameter sets are ascertained for at least one shim channel of a shim unit... before acquiring the magnetic resonance scan data from the first section, the at least one shim channel is set using a first shim parameter set... before acquiring the magnetic resonance scan data from the second section, the at least one shim channel is set using a second shim parameter set
Implementation Method 2
the body of an examination person... is exposed with by a basic field magnet to a relatively high basic magnetic field... Radio-frequency pulses... are then emitted... which leads to the nuclear spins of specific atoms excited in a resonant manner
Data Source
AI summary
To enable improved reconstruction of magnetic resonance (MR) image data from MR scan data acquired from an examination object using dynamic shimming in an MR scanner that has a shim unit with at least one shim channel, an examination region of the object is divided into multiple sections, a B0 field of the examination region is scanned, and a B0 field map is thereby generated, a number of shim parameter sets are determined for the shim channel using the B0 field map, with a first shim parameter set of the number of shim parameter sets being determined for a first section of the multiple sections, and a second shim parameter set of the multiple shim parameter sets is determined for a second section of the multiple sections. MR scan data of the examination region are acquired, but before acquiring the MR scan data from the first section, the shim channel is adjusted using the first shim parameter set and, before acquiring the MR scan data from the second section, the shim channel is adjusted using the second shim parameter set. MR image data are reconstructed from the MR scan data using the first B0 field map and the number of shim parameter sets.