Multi-Echo MR Imaging Phase Compensation for Concomitant Field Artifacts
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Solution Overview
Problem
In magnetic resonance (MR) imaging systems, multi-echo sequences suffer from signal loss due to destructive interference caused by concomitant fields, which result in poor image quality due to phase accumulation differences between spin and stimulated echo paths.
Innovation Solution
A method is implemented to determine and compensate for the accumulated phase effects of concomitant fields by calculating the phase deviations between RF pulses and applying corrective measures such as adjusting gradient timings, reassigning gradient directions, or deactivating flow compensation, ensuring that the phase accumulation relationship is maintained within a predefined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-echo imaging sequence is used to acquire MR signals, then imaging speed is improved, but signal loss occurs due to destructive interference from concomitant fields
Solution Approach 1:
The system performs preliminary calculation of accumulated phases due to concomitant fields before the actual imaging sequence execution. By predicting the phase accumulation for different echo paths in advance, the system can identify potential destructive interference issues and adjust parameters beforehand, preventing signal loss while maintaining the fast imaging capability
Solution Approach 2:
The system changes imaging parameters dynamically based on calculated phase accumulation values. When the deviation between first and second accumulated phases exceeds a threshold, the system adjusts parameters such as echo spacing, gradient amplitudes, or RF pulse timing to correct the phase relationship, thereby eliminating destructive interference while preserving the multi-echo imaging speed advantage
2Reliability
If gradient amplitudes are increased to improve signal strength, then signal-to-noise ratio is improved, but phase accumulation deviation due to concomitant fields increases
Solution Approach 1:
The system implements a feedback mechanism where the calculated accumulated phases from concomitant fields are used to determine necessary parameter adjustments. The feedback loop continuously monitors the phase relationship between different echo paths and automatically adjusts gradient amplitudes or timing parameters to maintain phase consistency, allowing high gradient amplitudes to be used without causing destructive interference
Solution Approach 2:
The system makes gradient amplitudes and timing parameters dynamic rather than fixed. Based on the calculated phase accumulation, the system dynamically adjusts gradient parameters during the imaging sequence to maintain the desired phase relationship between spin echo and stimulated echo paths, enabling flexible optimization of both signal strength and phase consistency
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 prevents signal loss and maintains image quality by accurately predicting and mitigating the influence of concomitant fields, allowing for better MR signal acquisition in MR systems.
Implementation Method 1
Concomitant Fields - Typical gradients are designed to cause a variation of the static magnetic field B0 in one direction. However, it follows from Maxwell's equations that the application of gradients gives rise to components of the magnetic field that are not aligned in the z-direction.
Implementation Method 2
The time-integral of the concomitant fields causes a phase accumulation, which can lead to destructive interference in fast spin echo measurements.
Implementation Method 3
In MR imaging systems, multi-echo sequences are known in which after a single RF excitation pulse, several refocusing pulses are applied to generate several spin echoes.
Data Source
AI summary
The present disclosure relates to operating an MR system in which MR signals of an object under examination are acquired in an examining region using a multi echo imaging sequence, in which an RF excitation pulse and a plurality of RF refocusing pulses are applied. The techniques include determining a first accumulated phase of a magnetization in the object under examination. Then, a second accumulated phase of the magnetization in the object under examination is determined due to concomitant magnetic fields occurring between a second pair of consecutive RF pulses. Finally, it is determined whether a deviation from the predefined relationship is larger than a threshold and, if this is the case, a measure is applied in view of the fact that the deviation is larger than the threshold.