MRI Pulse Sequence Timing for Eddy Field Mitigation
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Solution Overview
Problem
The fast spin echo (FSE) method in magnetic resonance imaging (MRI) suffers from image quality deterioration due to echo peak and phase shifts caused by eddy fields, particularly those with short time constants, which cannot be adequately compensated by existing hardware, leading to issues like uneven sensitivity and signal degradation.
Innovation Solution
The MRI apparatus extends the time between the RF pulse for excitation and the first RF pulse for refocusing by a predetermined extension time, incorporating spare time after the transient of the gradient magnetic field for dephasing, to effectively mitigate the influence of eddy components with short time constants, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the echo spacing is shortened to improve imaging speed, then productivity increases, but image quality deteriorates due to eddy field effects
Solution Approach 1:
The patent applies preliminary action by introducing a delay period between the gradient magnetic field transient and the refocusing pulse. This delay allows the eddy field to decay before the refocusing pulse is applied, preventing eddy-induced phase shifts and echo peak displacements. The delay time is specifically set to 1.0-3.0 times the time constant of the eddy field, ensuring effective suppression of eddy effects while maintaining efficient imaging speed.
2Manufacturing precision
If hardware compensation for eddy fields is improved, then image quality improves, but device complexity increases
Solution Approach 1:
The patent replaces complex hardware compensation mechanisms with a simpler temporal control approach. Instead of using additional hardware components to actively compensate for eddy fields, the invention uses a delay period in the pulse sequence timing to allow eddy fields to naturally decay. This substitution of mechanical/hardware solutions with temporal control simplifies the system while achieving the same goal of improving image quality.
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 results in improved image quality by reducing image degradation from eddy components with short time constants, even when the echo spacing is shortened, thereby alleviating issues like uneven sensitivity and signal degradation.
Implementation Method 1
echo peaks or phases of a spin echo signal and a stimulated echo signal are shifted due to an eddy field
Data Source
AI summary
A magnetic resonance imaging apparatus according to an embodiment includes a controller and an image reconstruction unit. The controller executes a pulse sequence having spare time during the time after transient of a gradient magnetic field for dephasing, applied in a readout direction after a radio frequency (RF) pulse for excitation is applied, until the first RF pulse for refocusing is applied in the case where imaging based on a fast spin echo method is performed. The image reconstruction unit reconstructs an image from magnetic resonance data collected by executing the pulse sequence.