MRI Magnet Current Calibration via Frequency Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Magnetic resonance imaging (MRI) systems face challenges in maintaining accurate magnetic field calibration due to aging effects in shunt resistances and superconducting magnet decay, leading to inefficient ramping procedures and reduced measurement accuracy, especially in low-field systems where field decay occurs more rapidly.
Innovation Solution
A calibration method that involves measuring the electric current through a basic-field magnet using a measuring element and a frequency measurement unit, calculating a calibration factor to account for deviations, and calibrating the system to accurately determine the electric current, thereby compensating for aging effects and ensuring precise magnetic field maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the target frequency is set as high as possible to maximize the decay window, then the duration before field decay requires re-ramping is extended, but in low-field systems with narrow bandwidth this approach is limited and field decay still occurs rapidly
Solution Approach 1:
The patent applies preliminary action by performing frequency measurements and calculating calibration factors before the ramping procedure. The system measures the actual frequency drift, calculates the necessary calibration adjustment, and prepares the correction factor in advance. This allows the magnet to be ramped to the correct field strength from the start, compensating for aging effects and preventing the need for frequent re-ramping due to field decay.
2Measurement precision
If the magnet is ramped down and up frequently to maintain field calibration in low-field systems, then measurement accuracy is maintained, but system downtime increases and productivity decreases
Solution Approach 1:
The patent implements feedback by continuously monitoring the actual frequency of the basic field magnet and comparing it to the target frequency. The system calculates calibration factors based on the measured frequency drift and applies corrections to the ramping procedure. This closed-loop feedback mechanism ensures field calibration accuracy is maintained while minimizing the frequency of full ramp cycles, thereby improving system availability and productivity.
3Ease of operation
If the shunt resistance is not calibrated, then the measuring element provides current values, but aging effects cause deviations between measured and actual current leading to inaccurate field calibration
Solution Approach 1:
The patent applies parameter changes by introducing calibration factors that adjust the relationship between the measured voltage across the shunt resistance and the actual current flowing through the magnet. The system measures the actual frequency drift caused by aging effects and calculates corresponding calibration factors that compensate for shunt resistance changes. This dynamic parameter adjustment maintains measurement precision despite aging effects without requiring physical replacement or manual recalibration of the shunt resistance.
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 method enhances the accuracy of electric current measurement and magnetic field calibration, allowing for more efficient and automated ramping procedures, reducing downtime, and maintaining optimal magnetic field strength over time, particularly in low-field MRI systems.
Implementation Method 1
measuring a voltage across the shunt and determining the current from the measured voltage and a resistance value of the shunt
Implementation Method 2
electromagnets for creating the basic field. Since for high magnetic fields high electric currents in the order of about 500 A have to be applied, it is advantageous to use superconducting magnets with a persistent switch as basic field magnets.
Implementation Method 3
superconducting magnets with a persistent switch as basic field magnets. When the optimal magnetic field is reached, the persistent switch, which is also superconducting, is closed and the current will flow for a long time period in the superconducting magnet
Implementation Method 4
a frequency measurement in the magnetic field of the basic-field magnet with a frequency measurement unit
Data Source
Figure 1
Figure 2~4
Figure 5~6
AI summary
The invention describes a calibration method for calibrating a measuring element for determining the electric current I flowing through a basic-field magnet of a magnetic resonance imaging system, comprising the steps: - performing a measurement with the measuring element, - performing a frequency measurement in the magnetic field of the basic-field magnet with a frequency measuring unit, wherein the measurement of the measuring element and the frequency measurement are corresponding to the same magnetic field of the basic-field magnet, - calculating a calibration factor based on the deviation between the measurement of the measuring element and the frequency measurement, - calibrating the measuring element or the electric current in the basic-field magnet based on the calibration factor. The invention further describes a ramping method, a system for calibrating a measuring element, a magnet power supply unit, a control unit and a magnetic resonance imaging system.