Gradient Magnetic Field Pre-Dephasing for MRI Switching Lag Correction
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Solution Overview
Problem
Magnetic resonance imaging systems face inaccuracies and artifacts due to switching lag, particularly in ultrashort echo time (UTE) sequences, where the delay in gradient magnetic field switching leads to incorrect association of magnetic resonance signals with spatial frequencies, resulting in distorted images.
Innovation Solution
The method involves pre-dephasing the gradient magnetic field before the acquisition of magnetic resonance echo signals, ensuring the gradient magnetic field value is correct at the time of signal acquisition, allowing for precise location of measurement signals in frequency space and shifting readout points to correct for switching lag, thereby optimizing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gradient magnetic field switching is performed rapidly to achieve high temporal resolution, then measurement precision improves, but switching lag causes spatial resolution inaccuracies and image artifacts
Solution Approach 1:
The patent applies pre-dephasing by switching on gradient fields before the actual measurement to account for switching lag. This preliminary action ensures that the gradient fields have stabilized and the phase encoding is complete before data acquisition begins, thereby eliminating spatial resolution inaccuracies while maintaining rapid temporal resolution
Solution Approach 2:
The patent measures the actual switching behavior of gradient fields and uses this information to adjust timing parameters. By monitoring the real switching lag and compensating for it in subsequent measurements, the system maintains both high temporal resolution and accurate spatial resolution
2Manufacturing precision
If gradient magnetic field switching is delayed to allow stabilization, then spatial resolution accuracy improves, but temporal resolution and measurement efficiency deteriorate
Solution Approach 1:
The patent performs gradient field switching and phase encoding in advance before the actual echo signal acquisition. This preliminary action allows the gradient fields to stabilize and complete their encoding function before measurement, ensuring spatial resolution accuracy without delaying the actual data acquisition process
Solution Approach 2:
The patent maintains continuous gradient field application during the measurement process, switching between different gradient configurations without complete interruption. This continuous action ensures that phase encoding remains effective throughout the measurement sequence, maintaining both accuracy and efficiency
3Reliability
If pre-dephasing is applied to correct switching lag, then image quality and spatial frequency association improve, but measurement sequence complexity increases
Solution Approach 1:
The patent applies pre-dephasing as a standard preliminary step in the measurement sequence, switching on gradient fields before each echo signal acquisition. This systematic approach ensures consistent correction of switching lag across all measurements, improving image quality while maintaining a structured and manageable sequence
4Speed
If gradient magnetic field switching is performed without pre-dephasing in UTE sequences, then measurement speed is maintained, but severe artifacts occur due to switching lag
Solution Approach 1:
The patent applies pre-dephasing specifically in UTE sequences by switching on gradient fields before the ultrashort echo time measurement. This preliminary action completes the phase encoding before the rapid signal decay occurs, eliminating severe artifacts while maintaining the fast measurement speed characteristic of UTE sequences
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 minimizes artifacts and improves image quality by ensuring accurate association of magnetic resonance signals with spatial frequencies, even in UTE sequences, by controlling the gradient magnetic field to prevent switching lag from affecting data acquisition.
Implementation Method 1
The gradient magnetic field varies the resonance frequency (Larmor frequency) and, for example, also the phase position of the magnetization deflected by an RF pulse in a spatially dependent manner
Implementation Method 2
The magnitude of the magnetization (in particular of the transverse magnetization, defined in a plane transversal to the previously described basic magnetic field) at a defined location of the examination subject can be determined from the readout point in k-space with the use of a Fourier transformation
Implementation Method 3
The deflection typically takes place by radiating a number of RF pulses
Data Source
AI summary
In the magnetic resonance image data acquisition and apparatus, raw magnetic resonance data are acquired at multiple points along a trajectory in k-space from first and second magnetic resonance echo signals caused by a radio-frequency excitation pulse. The course of the trajectory in k-space is established by adjusting a magnetic field value of a gradient magnetic field. The gradient magnetic field has a field value of a first point in time of the trajectory curve and a subsequently modified and at a layer second point in time, the gradient magnetic field has the same field value as that said first point in time. The second point in time is before or during the acquisition of the raw magnetic resonance data of the first magnetic resonance echo signal. The shift value for the trajectory is determined and the trajectory is shifted according to this shift value, and an image is reconstructed from the shifted raw magnetic resonance data of the trajectory.