MRI Echo Signal Correction for Nyquist Ghost Reduction
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Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in reducing ghosting artifacts, particularly the Nyquist ghost, which occurs due to alternating gradient readout polarity in Echo Planar Imaging (EPI), leading to inaccurate diagnoses and limitations in correcting these artifacts without compromising scanning speed or efficiency.
Innovation Solution
The MRI system employs sequence controlling circuitry to apply alternating readout gradients and image generating circuitry that corrects echo signals based on phase and magnitude differences between even and odd lines of k-space, generating correction maps to eliminate or reduce ghosting artifacts, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Echo Planar Imaging (EPI) with alternating gradient readout polarity is used to maintain scanning speed, then productivity is improved, but ghosting artifacts occur due to errors between even and odd line echo signals
Solution Approach 1:
The patent applies preliminary correction by calculating phase differences between even and odd line echo signals before image reconstruction. Correction maps are generated in advance based on these phase differences, and the correction is applied during the reconstruction process, thereby eliminating ghosting artifacts while maintaining the fast EPI scanning speed
Solution Approach 2:
The patent changes the phase parameter of the echo signals by calculating phase differences between even and odd lines. By adjusting the phase parameter through correction maps, the system compensates for the errors that cause Nyquist ghosting, thereby improving image accuracy without sacrificing scanning speed
2Measurement precision
If correction methods are applied to reduce ghosting artifacts, then image accuracy is improved, but scanning speed or efficiency is compromised
Solution Approach 1:
The correction maps are calculated in advance based on phase differences between even and odd line echo signals. This preliminary calculation allows the actual image reconstruction to apply correction efficiently without adding significant time, thus improving image accuracy while maintaining scanning speed
Solution Approach 2:
The system uses feedback from the measured phase differences between even and odd line echo signals to generate correction maps. This feedback mechanism allows the system to automatically adjust and compensate for errors, improving image accuracy without requiring manual intervention or additional scanning time
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 effectively reduces ghosting artifacts to levels below 2% under various scanning conditions, enhancing diagnostic image accuracy without sacrificing scanning speed or efficiency, and is applicable to a wide range of MRI applications.
Implementation Method 1
applies a excitation pulse and then continuously applies a readout gradient magnetic field with alternating polarity thereof and acquires echo signals continuously generated by the pulse sequence from a plurality of receive channels
Data Source
AI summary
A magnetic resonance imaging apparatus according to an embodiment includes sequence controlling circuitry and image generating circuitry. The sequence controlling circuitry executes a pulse sequence which applies a excitation pulse and then continuously applies a readout gradient magnetic field with alternating polarity thereof and acquires echo signals continuously generated by the pulse sequence from a plurality of receive channels. The image generating circuitry corrects the echo signals so as to generate an image, correcting the echo signals for all of the receive channels collectively on the basis of phase differences between echo signals corresponding to even lines of k-space and echo signals corresponding to odd lines of k-space, and corrects the echo signals for each of the receive channels individually on the basis of magnitude differences between echo signals corresponding to the even lines of k-space and echo signals corresponding to the odd lines of k-space.