MRI Gradient Pre-distortion for Slice Selection Accuracy
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Solution Overview
Problem
Current magnetic resonance imaging techniques fail to effectively correct slice-selection gradient pulses, leading to image artifacts due to deviations in the magnetic field, which cannot be corrected later, especially in methods requiring non-constant gradients.
Innovation Solution
A method is introduced to improve slice selection by applying a correction term to compensate for magnetic field changes in slice-selection gradient pulses using the transfer characteristic of the gradient system, specifically the gradient system transfer function (GSTF), allowing for pre-distortion of slice-selection gradient pulses to achieve nominal gradients during imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-distortion is applied to slice-selection gradient pulses using transfer characteristic, then gradient accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies pre-distortion to slice-selection gradient pulses by calculating correction terms based on the gradient system transfer function before the actual imaging sequence is executed. The pre-distorted gradient waveform is computed in advance to compensate for expected deviations, thereby improving gradient accuracy without requiring real-time complex computations during imaging.
Solution Approach 2:
The patent introduces the gradient system transfer function as an intermediary element that characterizes the system's frequency response. This transfer function serves as a mediator between the desired gradient waveform and the actual played-out gradient, enabling accurate prediction and correction of gradient deviations through pre-computed correction terms.
2Measurement precision
If non-constant slice-selection gradient pulses are used, then slice selection precision is improved, but image artifacts increase due to uncorrected magnetic field deviations
Solution Approach 1:
The patent applies preliminary anti-action by computing correction terms that anticipate and counteract the magnetic field deviations caused by non-constant slice-selection gradient pulses. These correction terms are derived from the gradient system transfer function and are applied in advance to the gradient waveform, preventing the formation of image artifacts before they occur during imaging.
Solution Approach 2:
The patent modifies the slice-selection gradient pulse parameters by applying pre-distortion that changes the gradient waveform's time-dependent characteristics. The correction terms adjust the gradient strength over time based on the transfer function's frequency response, enabling precise slice selection while compensating for system-specific deviations that would otherwise cause artifacts.
3Manufacturing precision
If gradient pre-distortion is applied to compensate eddy currents, then gradient fidelity is improved, but processing time increases
Solution Approach 1:
The patent performs gradient pre-distortion computations in advance, before the actual imaging sequence is executed. The correction terms based on the gradient system transfer function are calculated beforehand and stored, eliminating the need for time-consuming real-time computations during patient imaging while maintaining high gradient fidelity.
Solution Approach 2:
The patent replaces real-time iterative correction mechanisms with pre-computed correction terms derived from the gradient system transfer function. This substitution eliminates the need for complex real-time processing and feedback loops, significantly reducing processing time while maintaining accurate gradient reproduction.
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 corrects for deviations in slice-selection gradients, preventing image artifacts and ensuring accurate k-space trajectory registration, even in multidimensional excitations, by pre-distorting the slice-selection gradient pulses to match the nominal gradient waveform, thereby enhancing image quality.
Implementation Method 1
A magnetic resonance system typically has three gradient coils that generate gradients in the x, y, and z directions
Implementation Method 2
a slice-selection gradient pulse applied during or before the radio-frequency pulse
Data Source
AI summary
A method for recording a magnetic resonance image data set includes providing a magnetic resonance sequence. The magnetic resonance sequence includes at least one radio-frequency pulse and a slice-selection gradient pulse applied during or before the radio-frequency pulse, which is configured as non-constant. The method includes providing at least one correction term for compensating a magnetic field change of the slice-selection gradient pulse. The magnetic field change is ascertained via a transfer characteristic of the gradient system of the magnetic resonance system. The method also includes recording at least one magnetic resonance image data set with the magnetic resonance sequence using the correction term.