MRI Shim Unit Sub-Area Segmentation for Field Homogeneity
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Solution Overview
Problem
Modern magnetic resonance imaging (MRI) systems face challenges in achieving high homogeneity of the main magnetic field, particularly due to the inhomogeneities introduced by the examination subject, which can result in inferior image quality. Conventional dynamic shimming methods often rely on first-order shim channels for rapid adjustments, while higher-order shim channels are limited by slower settling times and higher costs.
Innovation Solution
The method involves dividing the examination area into sub-areas and determining specific shim parameter sets for each sub-area, using a first B0 field map to adjust first-order shim channels dynamically and a second shim parameter set for higher-order shim channels to maintain constant compensation, thereby optimizing the main magnetic field homogeneity across the entire examination area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If higher-order shim channels are used for field homogenization, then manufacturing precision of magnetic field homogeneity is improved, but device complexity and cost increase due to more powerful amplifiers and low-resistance wires
Solution Approach 1:
The patent divides the examination area into multiple sub-areas and assigns different shim parameter sets to each sub-area. This segmentation allows first-order shim channels to be optimized for rapid adjustments in specific regions, while higher-order shim channels provide global compensation, reducing the overall complexity compared to using higher-order channels throughout the entire volume.
Solution Approach 2:
The patent implements local quality by determining sub-area-specific shim parameter sets that are tailored to the magnetic field characteristics of each region. First-order shim channels are configured with location-dependent parameters to provide locally optimized compensation, while higher-order channels provide broader coverage, thereby improving field homogeneity without requiring high-power amplifiers for all channels.
2Manufacturing precision
If higher-order shim channels are adjusted dynamically, then magnetic field homogeneity is improved, but settling time increases making rapid adjustment impossible
Solution Approach 1:
The patent implements dynamic shimming by allowing first-order shim channel parameters to vary over time and space, with each sub-area having its own time-varying shim parameter set. This dynamic configuration enables rapid adaptation to changing magnetic field conditions in different regions without requiring higher-order channels to switch quickly, as they maintain constant compensation parameters.
Solution Approach 2:
The patent performs preliminary determination of sub-area-specific shim parameter sets based on a measured B0 field map before the actual MRI data acquisition. This preliminary action allows the system to pre-optimize the configuration of first-order shim channels for each sub-area, enabling rapid dynamic adjustments during scanning without requiring higher-order channels to settle quickly, as their parameters are determined in advance.
3Manufacturing precision
If dynamic shimming with multiple shim parameter sets is implemented, then magnetic field homogeneity is improved, but measurement time increases
Solution Approach 1:
The patent applies partial action by implementing dynamic shimming only for first-order shim channels on a per sub-area basis, while higher-order shim channels maintain constant parameters. This selective dynamic adjustment achieves improved field homogeneity in critical regions without requiring full dynamic optimization of all channels, thereby limiting the increase in measurement time to only what is necessary for the most impactful adjustments.
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 magnetic field inhomogeneities, leading to improved image quality by combining the rapid adjustments of first-order shim channels with the constant compensation of higher-order channels, resulting in more complete field homogenization and reduced artifacts in MRI data.
Implementation Method 1
a shim unit (35), in particular having a first shim channel set (36) with at least one first shim channel (36) and a second shim channel set (37) with at least one second shim channel (37)
Implementation Method 2
the body of the subject, especially a patient, is typically exposed to a relatively strong main magnetic field (B0 field), for example, 1.5, 3, or 7 Tesla, using a main magnet
Implementation Method 3
High-frequency pulses, such as excitation pulses, are then emitted via a radio frequency antenna unit using suitable antenna elements. This causes the nuclear spins of certain atoms, resonantly excited by these radio frequency pulses, to be tilted by a defined angle relative to the magnetic field lines
Implementation Method 4
During the relaxation of the nuclear spins, radio frequency signals, known as magnetic resonance signals, are emitted. These signals are received by suitable radio frequency antennas
Data Source
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AI summary
The invention relates to a method for magnetic resonance imaging, a magnetic resonance device, and a computer program. To enable improved adjustment of at least one shim channel for magnetic resonance imaging, the inventive method for magnetic resonance imaging in an examination area of an object under investigation, using a magnetic resonance device comprising a shim unit, wherein the shim unit comprises a first set of shim channels with at least one first shim channel and a second set of shim channels with at least one second shim channel, comprises the following process steps: - Dividing the examination area into several sub-areas, - Determining several first shim parameter sets for the at least one first shim channel, wherein one first shim parameter set of the several first shim parameter sets is determined for each of the several sub-areas.- Determining a second shim parameter set for the at least one second shim channel, taking into account the several first determined shim parameter sets; - Acquiring magnetic resonance image data of the investigation area of the object under investigation, wherein, prior to acquiring the magnetic resonance image data, the at least one second shim channel is set based on the second shim parameter set, and the at least one first shim channel is set for acquiring the magnetic resonance image data from a specific sub-area of the several sub-areas based on a first shim parameter set determined for the specific sub-area.