MRI Gradient Coil Frequency Correction via Temperature Feedback
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Solution Overview
Problem
MRI technologies face challenges in maintaining image quality due to shifts in the center frequency of magnetic resonance of hydrogen atoms caused by heat generation in gradient magnetic field coils, leading to inadequate fat suppression effects, especially in long-duration seriography.
Innovation Solution
An MRI apparatus and method that includes a gradient magnetic field coil unit, a temperature measuring unit, a data storing unit, and a pulse setting unit, which measure temperature variations, store shift data, and correct the center frequency of RF pulses based on estimated shifts to maintain image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gradient magnetic field coil generates significant heat during imaging, then imaging capability is maintained, but the center frequency of magnetic resonance shifts and fat suppression effect degrades
Solution Approach 1:
The system performs a prescan step before actual imaging to measure the initial center frequency of magnetic resonance and establish the relationship between temperature and frequency shift. This preliminary measurement enables subsequent real-time correction during imaging without interrupting the imaging process.
Solution Approach 2:
The system continuously monitors temperature of the gradient magnetic field coil during imaging and uses this feedback to dynamically adjust the center frequency of RF pulses. The control unit modifies the reference clock frequency based on temperature variations, ensuring the fat suppression pulse remains effective throughout the imaging process.
2Duration of action of moving object
If gradient magnetic field coil is operated for long duration, then imaging completeness is achieved, but heat generation increases and degrades image quality
Solution Approach 1:
The system pre-measures the temperature-frequency relationship during a prescan phase and stores this calibration data. This preliminary action allows the system to predict and compensate for frequency shifts that will occur during extended imaging without requiring continuous recalibration.
Solution Approach 2:
Temperature sensors continuously monitor the gradient coil temperature during extended imaging sequences, and the control unit dynamically adjusts the RF pulse center frequency in real-time based on this feedback, maintaining image quality throughout the entire imaging duration.
3Temperature
If cooling system is added to reduce heat, then temperature control is improved, but device complexity and cost increase
Solution Approach 1:
The system replaces mechanical cooling systems with an electronic frequency correction mechanism. Instead of physically cooling the gradient coil to prevent frequency shifts, the system electronically compensates for the frequency shifts by adjusting the RF pulse center frequency based on temperature measurements, thereby avoiding the complexity and cost of active cooling infrastructure.
4Manufacturing precision
If frequency correction is performed continuously, then image quality is maintained, but processing time and complexity increase
Solution Approach 1:
The system performs frequency correction at periodic intervals during imaging, triggered by temperature thresholds or timing events rather than continuously. The control unit adjusts the reference clock frequency at specific moments based on temperature measurements, maintaining image quality while minimizing processing overhead and avoiding unnecessary calculations.
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
The solution ensures high-quality images by accurately correcting RF pulse frequencies in real-time, minimizing the degradation of fat suppression effects over extended imaging times and reducing the need for extensive cooling, thereby reducing costs and allowing the use of gradient coils with high thermal conductivity.
Implementation Method 1
An MRI apparatus has a gradient magnetic field coil that applies a gradient magnetic field to an imaging space in which an object is placed
Implementation Method 2
The temperature measuring unit measures a temperature of the gradient magnetic field coil unit
Implementation Method 3
MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) set in a static magnetic field with an RF pulse having the Larmor frequency
Implementation Method 4
MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) set in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation
Data Source
AI summary
The temperature of an MRI gradient magnetic field coil unit is measured at least two times. Shift data indicating a center magnetic resonance frequency of a hydrogen atom in response to variation of the gradient coil temperature is stored in advance. Estimated shift of the center frequency based on the measurement result is determined and the center frequency of an RF NMR excitation pulse is corrected based on the estimated shift.