Adaptive RF Flip Angle for Segmented MR Image Alignment
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Solution Overview
Problem
Conventional magnetic resonance (MR) imaging systems face challenges in maintaining alignment between adjacent segments during segmented k-space reference line acquisition, leading to image artifacts due to patient movement and physiological changes, which affect the accuracy of GRAPPA reconstructed images.
Innovation Solution
The system acquires consecutive segments of k-space line data representative of an individual image slice in a gradient echo method by adaptively varying the RF excitation pulse flip angle between segments, minimizing the time interval between acquisitions and using a GRAPPA accelerated parallel imaging method to reduce artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional multi-shot or segmented EPI acquisition is used to match echo spacing between image data and reference data, then geometric distortion artifacts are reduced, but the time interval between adjacent segments becomes long (2-10 seconds), causing misalignment artifacts when patient moves
Solution Approach 1:
The system dynamically adjusts the RF excitation pulse flip angle for each segment based on the segment index and physiological parameters. By varying the flip angle adaptively across segments, the system optimizes signal intensity and maintains consistent echo spacing while reducing the time interval between segments, thereby minimizing misalignment artifacts caused by patient motion.
Solution Approach 2:
The invention changes the flip angle parameter adaptively for each segment acquisition. The flip angle is calculated as a function of the segment number and T1 relaxation time, allowing the system to maintain optimal signal characteristics across multiple segments while reducing the repetition time and minimizing motion-induced misalignment artifacts.
2Manufacturing precision
If segmented reference lines are acquired in consecutive-slice manner to match echo spacing, then geometric distortion is reduced, but respiratory or cardiac cycle variations cause misalignment and artifacts in GRAPPA reconstruction
Solution Approach 1:
The system employs dynamic flip angle adjustment that adapts to physiological variations. By calculating optimal flip angles based on segment index and estimated T1 values, the system compensates for signal intensity variations caused by respiratory and cardiac cycles, ensuring consistent reference data quality across segments.
Solution Approach 2:
The system uses feedback from the acquired signal intensity and physiological timing information to adjust the flip angle for subsequent segments. This feedback mechanism ensures that reference data maintains consistent quality and alignment across segments, reducing artifacts in GRAPPA reconstruction.
3Productivity
If GRAPPA accelerated parallel imaging is used to reduce readout time and echo spacing, then image blur and geometric distortion are reduced, but reference autocalibration data must be acquired with matched echo spacing, requiring multi-shot or segmented acquisition that increases time interval
Solution Approach 1:
The system changes the flip angle parameter adaptively across segments to maintain optimal signal characteristics while using segmented acquisition for reference data. This allows the system to match echo spacing requirements for GRAPPA reconstruction without requiring excessively long time intervals, as the adaptive flip angle compensation maintains data consistency.
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 image artifacts and maintains echo spacing, resulting in improved Signal to Noise Ratio (SNR) and motion insensitivity in image reconstruction, especially in applications like cardiac and functional brain imaging.
Implementation Method 1
an RF signal generator for generating RF excitation pulses in an anatomy and enabling subsequent acquisition of associated RF echo data
Implementation Method 2
a magnetic field gradient generator for generating magnetic field gradients for anatomical volume selection, phase encoding and readout RF data acquisition
Data Source
AI summary
A system for accelerated segmented magnetic resonance (MR) image data acquisition includes an RF (Radio Frequency) signal generator and a magnetic field gradient generator. The RF signal generator generates RF excitation pulses in anatomy and enabling subsequent acquisition of associated RF echo data. The magnetic field gradient generator generates magnetic field gradients for anatomical volume selection, phase encoding, and readout RF data acquisition in a three dimensional (3D) anatomical volume. The RF signal generator and the magnetic field gradient generator acquire consecutive segments of k-space line data representative of an individual image slice in a gradient echo method by adaptively varying RF excitation pulse flip angle between acquisition of the consecutive segments.