Gradient Field Cancellation for MR Imaging Distortion
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Solution Overview
Problem
Magnetic resonance systems face limitations in imaging regions outside their normally usable field of view due to B0 field inhomogeneities and gradient non-linearities, leading to distortions that cannot be compensated for in the phase coding direction, particularly affecting areas like arms and stomachs in MR-PET hybrid systems.
Innovation Solution
A method is introduced to create specific gradient fields that cancel out distortions caused by B0 field inhomogeneities and gradient non-linearities at predetermined positions, allowing for distortion-free imaging by selecting appropriate readout directions, enabling radial sampling to reduce distortions in multiple dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If imaging is performed in the edge area of the field of view, then the field of view coverage is improved, but imaging precision deteriorates due to B0 field inhomogeneities and gradient non-linearities
Solution Approach 1:
The patent applies local quality by creating different gradient fields for different regions of the field of view. Specifically, a first gradient field is created for a first region and a second gradient field for a second region, with each gradient field optimized for its specific area. This allows the edge areas to have tailored gradient characteristics that compensate for local B0 inhomogeneities and gradient non-linearities, thereby maintaining imaging precision while expanding field of view coverage.
Solution Approach 2:
The patent changes gradient field parameters (amplitude, direction, timing) to compensate for distortions in different regions. By adjusting the gradient field characteristics specifically for edge areas, the system optimizes the balance between field of view coverage and imaging precision. The gradient fields are modified to counteract the effects of B0 inhomogeneities and non-linearities in specific regions without affecting the entire field of view uniformly.
2Measurement precision
If gradient amplitude is optimized for one direction, then distortion is minimized in that direction, but distortion compensation capability deteriorates in other directions
Solution Approach 1:
The patent segments the field of view into multiple regions (first region and second region), each with its own optimized gradient field. This segmentation allows independent optimization of gradient parameters for each region, enabling distortion compensation in multiple directions simultaneously. Instead of using a single gradient field that can only optimize one direction, the system divides the imaging space and applies region-specific gradient fields.
Solution Approach 2:
The patent extends the solution from one-dimensional optimization to multi-dimensional optimization by introducing multiple gradient fields for different spatial regions and/or directions. This dimensional expansion allows the system to address distortions in multiple directions concurrently, transforming a single-direction optimization problem into a multi-dimensional solution space where each dimension (region/direction) has its own optimized parameters.
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 allows for accurate, distortion-free imaging of regions outside the standard field of view, enhancing applications like MR-PET hybrid systems, magnetic resonance-based interventions, and radiation treatment planning by reducing movement artifacts and aliasing, and enabling precise attenuation corrections.
Implementation Method 1
a distortion caused by a non-linearity of a gradient field
Implementation Method 2
a distortion caused by a B0 field inhomogeneity
Data Source
AI summary
A method for imaging a part region of an examination object in a magnetic resonance system. In an embodiment, a first and second gradient field are respectively created such that, at a respective first and second position at the edge of the field of view, a distortion caused by a non-linearity of the respective first and second gradient field, and a distortion caused by a Bo field inhomogeneity, cancel each other out. By way of the respective first and second gradient, respective first and second magnetic resonance data which contains the respective first and second position are acquired. A first and second respective readout direction, in which the respective first and second magnetic resonance data are acquired, are selected as a function of a location of the respective first and second position. From the magnetic resonance data, an image of the part region is defined.