Recursive RF Pulse Design for Segmented EPI Artifacts
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Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) using echo planar imaging (EPI) faces challenges in achieving high spatial resolution due to image distortion and blurring artifacts, particularly with increasing readout duration, and segmented EPI is vulnerable to motion and respiration-induced errors.
Innovation Solution
A recursive RF pulse design method is implemented in a multi-shot pulse sequence, where each RF pulse is designed to account for residual longitudinal magnetization, ensuring consistent signal levels across segments and reducing artifacts like ghosting, by using a computer system to compute and store RF pulse parameters for an MRI system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the readout duration is extended to achieve higher spatial resolution, then the image resolution is improved, but image distortion and blurring artifacts worsen
Solution Approach 1:
The patent applies segmentation by dividing the EPI readout into multiple segments or shots, where each segment acquires a portion of k-space. This allows the total readout duration to be extended for higher resolution without requiring a single continuous readout, thereby reducing the accumulation of distortion and blurring artifacts that occur with prolonged single-shot EPI.
2Object-affected harmful factors
If segmented EPI is used to reduce readout duration per segment, then image distortion is reduced, but temporal instability and motion-related errors increase
Solution Approach 1:
The patent implements preliminary action by acquiring all segments of a given slice sequentially in time before proceeding to the next slice, similar to the FLEET technique. This minimizes the time between segments and reduces the potential for motion and respiration-related errors between readouts, thereby improving temporal stability while maintaining the benefits of segmented acquisition.
3Object-affected harmful factors
If conventional segmented EPI is used to reduce readout duration, then image distortion is reduced, but the time between segments increases causing motion vulnerability
Solution Approach 1:
The patent applies preliminary action by acquiring all segments of a given slice sequentially in time before proceeding to the next slice. This minimizes the time between segments and reduces the potential for motion and respiration-related errors between readouts, thereby improving temporal stability while maintaining the benefits of segmented acquisition.
4Measurement precision
If variable flip angle scheme is used to maximize signal, then SNR is improved, but slice profile consistency across segments deteriorates
Solution Approach 1:
The patent applies dynamics by implementing a variable flip angle scheme where the flip angle is adjusted for each segment based on the desired slice profile and the effects of longitudinal magnetization from previous segments. This dynamic adjustment allows the system to maximize signal and improve SNR while maintaining slice profile consistency across segments, overcoming the limitation of conventional fixed flip angle approaches.
5Productivity
If parallel imaging is used to accelerate readout, then acquisition time is reduced, but signal-to-noise ratio and image quality deteriorate
Solution Approach 1:
The patent combines segmentation with parallel imaging by dividing the EPI readout into multiple segments and applying parallel imaging techniques within each segment. This approach allows for readout acceleration while maintaining higher SNR compared to high acceleration factors, as the segmentation reduces the burden on any single parallel imaging reconstruction and allows for optimized acquisition parameters in each segment.
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 high-resolution EPI with improved signal-to-noise ratio and reduced motion-related errors, allowing for whole-brain imaging without prolonging the echo time, while being compatible with parallel imaging techniques.
Implementation Method 1
Conventional magnetic resonance imaging ('MRI') using echo planar imaging ('EPI') acquires two-dimensional images of a subject in a single readout
Data Source
AI summary
Described here are systems and methods for producing images with a magnetic resonance imaging (“MRI”) system using a high-resolution, motion-robust, artifact-free segmented echo planar imaging (“EPI”) technique. In particular, a fast low angle excitation echo planar imaging technique (“FLEET”) using variable flip angle (“VFA”) radio frequency (“RF”) excitation pulses that are recursively designed to have a flat magnitude and phase profile across a slice for a range of different flip angles by accounting for longitudinal magnetization remaining after each preceding RF pulse is applied.