MRI Gradient Pulse Correction via Current-to-Field Transfer Function
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Solution Overview
Problem
The existing gradient systems in MRI scanners face challenges in predicting and compensating for non-linearities in gradient amplifiers, leading to compromised image quality due to unpredictable field responses, especially in selection gradients used for MR signal encoding.
Innovation Solution
A gradient system that incorporates a current sensor system to sample electrical currents and apply a current-to-field modulation transfer function (CGMTF) to predict and correct actual selection gradient pulse shapes, allowing for adaptive RF pulse shaping to compensate for distortions, thereby minimizing the need for continuous monitoring of output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous monitoring of output currents is implemented to accurately predict gradient field responses, then image quality improves, but device complexity and cost increase
Solution Approach 1:
The system performs preliminary measurement of the current-to-field transfer function (CGMTF) during a calibration phase before actual imaging. This pre-characterization of the gradient coil system allows the reconstruction to use stored transfer function data without requiring continuous monitoring during imaging, thus resolving the contradiction between measurement accuracy and device complexity
Solution Approach 2:
Instead of continuously measuring actual output currents during imaging, the system uses a measured transfer function (CGMTF) that copies the relationship between current and field. This allows accurate field prediction through calculation rather than continuous physical measurement, reducing device complexity while maintaining prediction accuracy
2Ease of manufacture
If simpler and cheaper gradient amplifier components are used, then device cost decreases, but non-linearity effects increase making waveform prediction difficult
Solution Approach 1:
The system measures the actual output current and uses the measured CGMTF to calculate the true k-space trajectory, providing feedback-based correction. This allows the use of simpler amplifiers while maintaining reliable waveform prediction through measurement and computational correction of non-linearities
Solution Approach 2:
The patent replaces the need for expensive, highly linear gradient amplifiers with a computational approach. By measuring currents and using transfer function-based calculation to determine actual field trajectories, the system substitutes hardware precision requirements with software-based correction, enabling use of simpler amplifiers while maintaining reliability
3Device complexity
If current-based correction is applied only to readout gradients, then device complexity remains low, but image quality is compromised in regions requiring selection gradients
Solution Approach 1:
The patent implements a universal current sensing and correction approach that applies to all gradient directions (selection, phase, and readout gradients). The same CGMTF-based correction methodology is used for all gradient coils, providing comprehensive spatial encoding accuracy across all imaging regions without requiring different systems for different gradient types
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 improves image quality by accurately predicting and correcting gradient field distortions, ensuring optimal performance of selection gradients without the need for continuous monitoring of output currents, thus enhancing the control of gradient fields.
Implementation Method 1
at least one gradient coil for generating the gradient magnetic field when supplied with electrical current
Implementation Method 2
a current sensor system configured for sampling an electrical current supplied to the gradient coil
Data Source
AI summary
For a gradient system (102, 300) for a magnetic resonance imaging system (100) a solution for improving the control of gradient fields for a higher image quality shall be created. This is achieved by a gradient system (102, 300) the gradient system (102, 300) comprising: at least one gradient coil (110, 310) for generating the gradient magnetic field when supplied with electrical current, wherein the gradient coil (110, 310) is configured for generating at least one selection gradient magnetic field by transmitting selection gradient pulses, wherein the gradient system (102, 300) comprises a gradient coil amplifier (112, 308) configured for supplying the electrical current to the gradient coil (110, 310), the gradient system (102, 300) further comprising a current sensor system (113, 312) configured for sampling an electrical current supplied to the gradient coil (110, 310) by the gradient coil amplifier (112, 308), wherein the gradient system (102, 300) is further configured to obtain an actual selection gradient pulse shape (304) of the selection gradient magnetic field by applying a current to field modulation transfer function (CGMTF) to the sampled electrical current, which enables a magnetic resonance examination system (100) to compensate for the deviation of the actual selection gradient pulse shape (304) from an input selection gradient pulse shape (302) by adjusting radio frequency pulses (316) emitted simultaneously with the selection gradient pulses. The present invention also concerns a magnetic resonance imaging system (100), a method of operating a gradient system (102, 300) and a computer program product.