MRI Partially Parallel Acquisition Calibration Triggering
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Solution Overview
Problem
Magnetic resonance imaging using partially parallel acquisition with multiple component coils faces challenges in avoiding movement artifacts while maintaining high image resolution and quality, particularly in 3D acquisitions where the acquisition time is not short enough to freeze periodic movements, leading to ghost artifacts and inconsistencies in calibration data.
Innovation Solution
Implementing a calibration measurement and an actual measurement in separate time periods, both triggered by identical states of the examination subject, such as heartbeat or breathing cycles, to ensure coherent calibration data and reduce acquisition time, allowing for the reconstruction of complete image data sets without movement artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the acquisition time is extended to acquire complete k-space data for high-resolution 3D imaging, then image resolution is improved, but movement artifacts increase due to periodic movements like breathing
Solution Approach 1:
The patent applies preliminary action by acquiring calibration data in a first time period before acquiring the actual image data in a second time period. Both acquisitions are triggered by identical states of the examination subject (e.g., same phase in breathing cycle), ensuring that the calibration data reflects the same physiological state as the image data. This preliminary calibration step enables subsequent reconstruction algorithms to correctly combine the undersampled k-space data without introducing movement artifacts, thus achieving high resolution imaging despite the shortened acquisition time.
2Productivity
If reference lines are acquired separately beforehand to reduce acquisition time, then productivity is improved, but measurement precision deteriorates due to inconsistencies between calibration data and image data
Solution Approach 1:
The patent employs periodic action by triggering both the calibration data acquisition and the image data acquisition using identical periodic triggers, such as the same phase of the breathing cycle or heartbeat. This ensures that both measurements are taken under the same physiological conditions. The systematic use of periodic triggering maintains coherence between the calibration data and image data while enabling separate acquisition sequences that reduce overall acquisition time, thus resolving the contradiction between productivity and measurement precision.
3Loss of time
If the number of k-space lines is reduced to shorten acquisition time, then loss of time is reduced, but loss of information increases due to incomplete data sampling
Solution Approach 1:
The patent introduces an intermediary element in the form of calibration data that serves as a bridge between the undersampled k-space data and the complete image reconstruction. The calibration data, acquired under identical physiological conditions, provides the necessary information about the relationship between different coil elements and the spatial encoding. This intermediary calibration information enables reconstruction algorithms to accurately reconstruct the complete image from the reduced number of k-space lines, thus recovering the information that would otherwise be lost due to undersampling.
Data Source
AI summary
In a method and system for magnetic resonance imaging of an examination subject on the basis of partially parallel acquisition (PPA) with multiple component coils, a calibration measurement is implemented in a first time period and an actual measurement for the imaging is implemented in a subsequent second time period. In the calibration measurement, calibration data for predetermined calibration points in spatial frequency space are acquired with the multiple component coils. In the actual measurement, incomplete data sets are respectively acquired in spatial frequency space with each of the multiple component coils. Complete data sets are reconstructed from the incomplete data sets and the calibration data. The first time period and the second time period are different, and the measurements are implemented when triggered in the two time periods. An essentially identical state of the examination subject or of the measurement system is used as a trigger.