EPTI MRI Zigzag k-t Sampling for Distortion-Free Imaging
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Solution Overview
Problem
Echo planar imaging (EPI) techniques suffer from geometric distortions and blurring, particularly in phase-encoding direction and limited ability to obtain multiple-contrast images, which compromises image quality in functional, diffusion, and perfusion imaging.
Innovation Solution
The method involves sampling a hybrid space along a zigzag trajectory in k-t space, spanning a temporal dimension and a phase-encoding dimension, allowing for the reconstruction of multi-contrast images without B0 distortions or T2* blurring, using techniques like subspace-constrained reconstruction and interleaved phase encoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-shot EPI is used for fast imaging, then acquisition speed is improved, but geometric distortion and blurring occur due to T2/T2* decay and susceptibility-induced phase accumulation
Solution Approach 1:
The patent segments the k-t space sampling into multiple interleaved phase-encoding lines acquired at different times. Instead of acquiring all phase-encoding lines in a single shot, the method divides them into multiple segments that are interleaved in the phase-encoding direction, allowing temporal separation of acquisitions while maintaining fast imaging speed.
Solution Approach 2:
The patent introduces a temporal dimension to the traditional k-space sampling by acquiring phase-encoding lines at different time points. This transforms the problem from a 2D k-space sampling issue to a 3D k-t space sampling problem, enabling separation of distortion and blurring effects through temporal encoding.
2Adaptability or versatility
If multi-echo EPI is used to obtain multiple-contrast images, then contrast versatility is improved, but the number of echoes is limited and distortion/blurring problems persist
Solution Approach 1:
The patent adds a temporal dimension to multi-echo EPI by acquiring multiple phase-encoding lines at different echo times within a single TR. This allows reconstruction of multiple contrast images (T2-weighted, T2*-weighted, etc.) from a single acquisition, eliminating the need for separate multi-echo sequences while maintaining image quality through proper temporal sampling.
Solution Approach 2:
The patent makes a single EPI acquisition serve multiple functions by simultaneously capturing data for multiple contrast types. Through interleaved phase-encoding and multi-echo sampling, one acquisition sequence generates multiple contrast-weighted images, making the imaging protocol universally applicable to various functional, diffusion, and perfusion imaging needs.
3Manufacturing precision
If fully-sampled ky-t space is acquired to eliminate distortion and blurring, then image quality is improved, but scan time becomes extremely long especially for high-spatial resolution
Solution Approach 1:
The patent applies partial sampling in the temporal dimension by acquiring only a subset of phase-encoding lines at each echo time, rather than fully sampling the entire k-t space. Through interleaved acquisition and iterative reconstruction, the method achieves distortion-free and blurring-free images with significantly reduced scan time compared to complete k-t space sampling.
Solution Approach 2:
The patent changes the sampling parameters by using variable temporal spacing between phase-encoding lines. Instead of uniform sampling, the method employs non-uniform temporal spacing that is optimized for the specific application, allowing efficient coverage of k-t space with reduced acquisitions while maintaining image quality through adaptive reconstruction algorithms.
Data Source
AI summary
Systems and methods for magnetic resonance imaging (“MRI”) that address the geometric distortions and blurring common to conventional echo planar imaging (“EPI”) sequences, and that provide new temporal signal evolution information across the EPI readout, are described. Echo planar time-resolved imaging (“EPTI”) schemes are described to implement an accelerated sampling of a hybrid space spanned by the phase encoding dimension and the temporal dimension. In general, each EPTI shot covers a segment of this hybrid space using a zigzag trajectory with an interleaved acceleration in the phase-encoding direction. The hybrid space may be undersampled and a tilted reconstruction kernel used to synthesize additional data samples.