Echo-Shifted EPI Blip Reversal for MRI Distortion Correction
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Solution Overview
Problem
Conventional echo-planar imaging (EPI) methods suffer from geometric distortions due to magnetic field inhomogeneities and off-resonance effects, requiring separate blip-up and blip-down acquisitions that double scan time and compromise temporal resolution, especially in BOLD functional MRI.
Innovation Solution
The esEPI-BUDA technique integrates blip-up and blip-down acquisitions into a single shot using echo-shifting, allowing two k-space datasets to be acquired with reversed phase-encoding gradients, followed by joint image reconstruction to correct geometric distortions without increasing scan time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate blip-up and blip-down acquisitions are performed to correct geometric distortion, then distortion correction quality is improved, but scan time is doubled
Solution Approach 1:
The patent combines blip-up and blip-down acquisitions into a single multi-echo sequence where both phase-encoding directions are acquired within one shot. The first echo-train acquires data with blip-up gradients while the second echo-train acquires data with blip-down gradients, merging what were previously two separate acquisitions into one unified sequence that corrects geometric distortion without doubling scan time.
2Manufacturing precision
If two separate acquisitions are used for distortion correction, then sufficient information for correction is obtained, but temporal resolution is compromised
Solution Approach 1:
The patent implements continuous acquisition of both blip-up and blip-down data within a single continuous sequence without interruption between acquisitions. This continuous multi-echo approach maintains temporal resolution by eliminating the gap and repetition inherent in separate acquisitions, while still gathering sufficient information from both phase-encoding directions for accurate distortion correction.
3Manufacturing precision
If longer scan times are used for separate acquisitions, then distortion correction is more accurate, but motion vulnerability increases
Solution Approach 1:
The patent merges blip-up and blip-down acquisitions into a single shot that is completed before subject motion can significantly alter the anatomy. This unified acquisition approach reduces motion vulnerability by eliminating the time gap between opposite phase-encoding directions, ensuring both datasets reflect the same anatomical state while maintaining accurate distortion correction.
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 scan time by half while minimizing phase variations and motion sensitivity, producing distortion-free images with improved SNR and temporal resolution in BOLD functional MRI.
Implementation Method 1
conventional phase-encoding with a stepping gradient is employed in one spatial dimension (e.g., the z-axis or the 'slice' direction), while EPI-type phase encoding with blip gradients is applied to the second spatial dimension
Implementation Method 2
three-dimensional (3D) acquisitions using gradient-echo echo-planar imaging (GRE-EPI)
Implementation Method 3
Blood oxygenation level-dependent (BOLD) functional MRI (fMRI) is a primary technique for mapping neural activity of the human brain
Data Source
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AI summary
The present disclosure provides an example method for using an MRI system electrically coupled to a computing device. The method includes generating, via the MRI system, an echo-shifted echo- planar imaging with blip up/down acquisition ("esEPI-BUDA") pulse sequence including a first radiofrequency ("RF") pulse and a second RF pulse, the first RF pulse followed by a first echo- train that is interleaved with the first and the second RF pulses, and the second RF pulse followed by a second echo-train such that the first and the second echo-trains have opposite phase-encoding blip gradient polarities to traverse echo planar imaging ("EPI") k-space in a reversed order. In response to the pulse sequence being generated, the MRI system acquires two k-space datasets within a single shot and corrects image distortion, via the MRI system, based on the two acquired k-space datasets.