GRAPPA Calibration Data Recording for MRI
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Solution Overview
Problem
Current methods for recording calibration data in magnetic resonance imaging, particularly for GRAPPA algorithms in echo planar imaging, face challenges such as long recording times, geometrical distortion mismatch, and patient movement-induced inconsistencies, leading to reduced image quality and increased susceptibility to artifacts.
Innovation Solution
The method involves scanning at least one segment of k-space in the readout direction during fully sampled phase encoding, with the segment extending around the k-space center and matching the phase encoding bandwidth of the measurement data, allowing for rapid, movement-insensitive reference scans with high signal-to-noise ratio calibration data suitable for both inplane and slice GRAPPA algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If calibration data are recorded in preliminary reference scans with high phase encoding bandwidth, then geometrical distortion matching is improved, but recording time increases and patient movement artifacts worsen
Solution Approach 1:
The patent segments k-space into multiple segments in the readout direction, recording calibration data for each segment separately. This allows the phase encoding bandwidth to be matched to the diagnostic scan while reducing the total recording time by distributing the calibration acquisition across multiple shorter segments rather than requiring a single long high-bandwidth scan
Solution Approach 2:
The patent changes the phase encoding bandwidth parameter during calibration data recording to match that of the subsequent diagnostic measurement scan. This parameter adaptation ensures geometrical distortion consistency between calibration and diagnostic scans while using the segmented k-space approach to maintain acceptable recording times
2Measurement precision
If fully sampled reference scans are used for calibration, then calibration data quality is improved, but recording time increases significantly
Solution Approach 1:
The patent applies segmentation to k-space by dividing it into multiple segments along the readout direction. For each segment, calibration data are acquired with full sampling in the phase encoding direction, ensuring high calibration data quality while the segmented approach distributes the total acquisition time across multiple shorter scans, reducing the impact of patient movement and physiological variations
Solution Approach 2:
The patent uses partial action by recording calibration data for only selected segments of k-space rather than the entire k-space. This partial sampling approach provides sufficient calibration information for GRAPPA kernel estimation while significantly reducing the total recording time compared to complete k-space sampling
3Productivity
If multiple slices are recorded simultaneously with undersampling, then productivity is improved, but reconstruction complexity increases
Solution Approach 1:
The patent segments k-space in the readout direction and records calibration data for each segment separately. This segmentation enables the development of efficient reconstruction algorithms that can handle simultaneously recorded slices by processing each segment independently, thereby managing reconstruction complexity while maintaining high imaging speed through parallel slice acquisition
Solution Approach 2:
The patent performs preliminary recording of calibration data for each k-space segment before the actual diagnostic scan. These pre-recorded calibration data are used to estimate GRAPPA kernels that account for the simultaneous multi-slice acquisition and undersampling pattern, simplifying the reconstruction process by preparing correction factors in advance
Data Source
AI summary
In a method and magnetic resonance (MR) apparatus for recording calibration data for establishing convolution kernels for GRAPPA algorithms for reconstruction of image data from measurement data recorded using echo planar imaging with simultaneous recording of a number of slices of a slice stack. A slice GRAPPA algorithm is used to reconstruct the image data of the individual slices and an inplane GRAPPA algorithm is used to reconstruct undersampled magnetic resonance data within the slices. In order to record the calibration data to be used for establishing the convolution kernels of the two GRAPPA algorithms, in a predetermined slice order for the slices of the slice stack, for one slice in each case, at least one segment of k-space to be sampled is read out in the readout direction for a completely sampled readout in the phase encoding direction, and at least one such segment extends around the center of k-space in the readout direction, and the segment width is selected so that the phase encoding bandwidth matches that of the recording of the measurement data.