Parallel Acquisition MRI Echo Train Calibration
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Solution Overview
Problem
Existing parallel acquisition techniques in magnetic resonance tomography face challenges in acquiring movement-insensitive and fast coil calibration data, particularly for sequence techniques like echoplanar imaging, leading to unsatisfactory data quality and increased sensitivity to patient movements due to time intervals and T2* decay inconsistencies.
Innovation Solution
The method involves generating two echo trains with identical sequence techniques, where the first echo train densely scans k-space for coil calibration data and the second echo train undersamples k-space for image data, with a shorter time interval between echoes in the first train, matching phase coding speed and T2* decay to minimize distortion artifacts and reduce acquisition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If coil calibration data are acquired separately before or after the measurement, then the measurement time is reduced, but the sensitivity to patient movements increases and data quality deteriorates
Solution Approach 1:
The patent combines the acquisition of coil calibration data and image data into a single measurement process. The first echo train acquires coil calibration data while the second echo train acquires image data, both within the same measurement sequence. This merging eliminates the need for separate calibration measurements, reducing total measurement time while ensuring both data sets are acquired under identical patient positioning and physiological conditions, thereby maintaining movement insensitivity.
Solution Approach 2:
The coil calibration data are acquired as a preliminary step within the same measurement sequence before the image data acquisition. The first echo train collects calibration data that are then used for parallel image reconstruction during the second echo train. This preliminary action within the unified sequence ensures calibration data are obtained without requiring separate measurement time, while both data sets remain sensitive to the same patient movements.
2Productivity
If the time interval between echoes is extended to cover more k-space lines, then the acquisition speed increases, but T2* decay inconsistencies and distortion artifacts increase
Solution Approach 1:
The patent applies different echo train configurations for different acquisition purposes within the same sequence. The first echo train uses shorter time intervals between echoes optimized for coil calibration data, while the second echo train uses longer time intervals optimized for image data. This local optimization allows each echo train to achieve its specific goals without compromising overall image quality or introducing T2* decay inconsistencies.
Solution Approach 2:
The patent changes the echo train parameters (time interval between echoes) depending on the acquisition phase. During coil calibration acquisition, shorter echo intervals are used to minimize T2* decay. During image data acquisition, longer echo intervals are used to cover more k-space lines. This parameter adaptation allows the system to optimize for speed when appropriate while maintaining image quality when needed.
3Loss of time
If parallel acquisition techniques are applied with undersampling, then the measurement time is reduced, but aliasing artifacts and reconstruction complexity increase
Solution Approach 1:
The patent performs preliminary acquisition of coil calibration data using a densely sampled first echo train before acquiring undersampled image data in the second echo train. These pre-acquired calibration data are then used during parallel image reconstruction to resolve the aliasing artifacts caused by undersampling. This preliminary calibration step simplifies the reconstruction process compared to methods that attempt to calibrate and undersample simultaneously, as the calibration parameters are already determined from the high-quality reference data.
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 enables robust, movement-insensitive parallel image reconstruction with improved signal-to-noise ratio and reduced acquisition time, effectively addressing the limitations of previous methods by maintaining data quality under typical patient movements.
Implementation Method 1
Magnetic resonance tomography (MRT)... generating a first echo train after a first excitation pulse... generating a second echo train after a second excitation pulse
Data Source
AI summary
In a magnetic resonance a method and apparatus to generate images by a parallel acquisition technique, a first echo train is generated after a first excitation pulse, wherein the first echo train sufficiently densely scans a segment of k-space to be scanned for an acquisition of coil calibration data. Coil calibration data are acquired by means of the first echo train after the first excitation pulse. The acquired coil calibration data are stored in a coil calibration data set. A second echo train is generated after a second excitation pulse, wherein the second echo train undersamples a segment of k-space to be scanned for an acquisition of image data. Image data are acquired by means of the second echo train after the second excitation pulse. The acquired image data are stored in an incomplete image data set. An image data set is generated by substituting data missing in the incomplete image data set due to the undersampling by means of a selected PAT reconstruction technique using the coil calibration data. The first echo train and the second echo train are generated by an identical sequence technique such that each echo train has a series of echoes, with a time interval between successive echoes of the first echo train being shorter than a time interval of the second echo train.