Diffusion Weighted MRI Nyquist Ghost Suppression via Echo Swapping
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Solution Overview
Problem
Existing diffusion weighted magnetic resonance imaging (DWI) techniques face challenges in suppressing Nyquist ghosts, which are artifacts introduced due to phase errors and timing differences, particularly affecting image quality and signal intensity in pathological conditions like stroke, where conventional methods like PLACE are not suitable for DWI as they decrease signal magnitude.
Innovation Solution
The method involves acquiring multiple k-space data sets using slightly different DWI pulse sequences, swapping odd and even-numbered echoes, and reconstructing magnetic resonance images from each set to average their magnitudes, generating an average magnitude image that suppresses Nyquist ghosts without reducing signal intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the PLACE method is used to suppress Nyquist ghost, then the ghost artifact is reduced, but the signal magnitude is substantially decreased
Solution Approach 1:
The patent segments the k-space data acquisition into multiple separate acquisitions with different phase-encoding directions. By dividing the single acquisition into multiple segments and processing them separately before combining, the method suppresses Nyquist ghosts while preserving signal magnitude through selective combination of magnitude images rather than complex k-space averaging.
Solution Approach 2:
Instead of averaging complex k-space data as in the PLACE method, the patent inverts the approach by first reconstructing images from multiple acquisitions and then averaging the magnitude values. This reversal of the processing sequence prevents signal cancellation while still eliminating Nyquist ghost artifacts.
2Device complexity
If conventional MRI sequences are used, then the imaging process is simple, but signal intensity does not change until at least 8 hours after stroke onset
Solution Approach 1:
The patent changes the imaging parameters by using diffusion-weighted imaging sequences with specific b-values and gradient configurations. This parameter modification enables detection of acute stroke changes as early as 30 minutes after onset, dramatically reducing the detection time compared to conventional T2-weighted imaging while maintaining clinical feasibility.
3Object-affected harmful factors
If multiple k-space data sets are acquired with different pulse sequences, then Nyquist ghost is suppressed, but the acquisition time increases
Solution Approach 1:
The patent employs periodic action by acquiring multiple k-space data sets in a structured sequence with alternating phase-encoding directions. This periodic acquisition pattern allows for efficient data collection that can be processed to suppress Nyquist ghosts while managing acquisition time through optimized pulse sequence design.
Data Source
AI summary
Systems and methods for suppressing Nyquist ghost for diffusion weighted magnetic resonance imaging are disclosed. An exemplary method includes acquiring multiple k-space data sets using multiple sets of diffusion weighted imaging pulse sequences, reconstructing a magnetic resonance image from each of the multiple k-space data sets respectively, and averaging magnitudes of the magnetic resonance images to generate an average magnitude magnetic resonance image.