3D Spin Echo MR Imaging Phase Inversion for FID Artifact Reduction
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Solution Overview
Problem
Fast 3D spin echo MR imaging sequences produce artifacts due to FID signals from regions outside the selectively excited volume, complicating diagnosis in areas like the spine, hip, or pelvis.
Innovation Solution
A method using multiple reception coils to acquire partially sampled raw datasets with RF excitation and refocusing pulses of opposite phases, allowing for the calculation of a weighting matrix to synthesize missing data points and combine datasets, reducing FID artifacts by canceling out signals outside the excited area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If non-selective refocusing pulses are used after selective RF excitation, then the imaging sequence can cover entire volumes, but FID signals from outside the selectively excited volume cause artifacts
Solution Approach 1:
The patent applies phase inversion by alternating the phase of refocusing pulses between +180° and -180°. This inversion causes FID signals from outside the selective excitation volume to have opposite phases and cancel each other out, while spin echo signals from the desired volume maintain constructive interference. This resolves the contradiction by eliminating harmful FID artifacts while preserving complete volume coverage capability.
Solution Approach 2:
The patent converts the harmful FID signals into beneficial cancellation effects. By using alternating phase refocusing pulses, the FID signals that would normally create artifacts are instead made to interfere destructively with each other, transforming them from harmful artifacts into a mechanism for suppressing unwanted signals from outside the region of interest.
2Measurement precision
If the raw dataspace is fully sampled according to the Nyquist theorem, then complete image reconstruction is achieved, but acquisition time increases
Solution Approach 1:
The patent implements partial sampling of the raw dataspace by acquiring only a subset of k-space lines (e.g., every other line or a reduced number of phase-encoding steps). This partial action reduces acquisition time significantly while still enabling complete image reconstruction through the combination of multiple undersampled datasets with alternating phase refocusing pulses, which together provide sufficient information for full image recovery.
3Object-generated harmful factors
If multiple undersampled datasets with alternating phase are acquired and combined, then FID artifacts are reduced, but data processing complexity increases
Solution Approach 1:
The patent segments the complete k-space acquisition into multiple separate undersampled datasets, each acquired with alternating phase refocusing pulses. Each segment is independently undersampled to reduce individual acquisition time, and then all segments are combined through straightforward addition or averaging. This segmentation approach reduces FID artifacts through phase cancellation while keeping the processing operation simple and computationally efficient.
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 or eliminates FID artifacts in 3D MR images, shortening acquisition time and enabling more accurate imaging without the need for full sampling of the raw dataspace, while using parallel imaging techniques like GRAPPA or CAIPIRINHA for data reconstruction.
Implementation Method 1
Magnetic resonance method for artifact prevention in fast 3D spin echo sequences
Implementation Method 2
generate at least one first spin echo
Implementation Method 3
acquired in a first raw dataset in the three-dimensional raw dataspace (k-space) using multiple reception coils
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for creating an MR 3D image dataset, spin echo sequences are used to acquire two raw datasets that are each undersampled, wherein the excitation pulses or the refocusing pulses radiated in the data acquisitions have an opposite phase for the two raw datasets. These two raw datasets are combined into a combined 3D raw dataset that is not undersampled, and a weighting matrix is calculated for use in calculating the raw data points that were not acquired in the first raw dataset and the raw data points not acquired in the second raw dataset. A first complete raw dataset and second complete raw dataset are thereby calculated, which are then combined. The MR 3D data is then reconstructed from tis combined raw dataset.