Pulsed Compensation Gradients for MR Field Homogeneity
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Solution Overview
Problem
Existing MR systems with superconducting magnets face high costs and limited space due to the need for complex designs and helium cooling, with shim coils only capable of correcting small magnetic field inhomogeneities, making them uncomfortable for patients and costly to maintain.
Innovation Solution
The use of pulsed compensation magnetic field gradients with temporally variable currents to reduce magnetic field inhomogeneity during MR imaging sequences, allowing for less stringent homogeneity requirements and simpler magnet designs, enabling greater space for the patient and reduced helium consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If superconducting magnets with many coil elements are used to achieve high field homogeneity, then the polarization field homogeneity is improved, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal shim coil current settings that compensate for known field inhomogeneities before the actual MR imaging sequence begins. This allows the system to use simpler magnets with fewer coil elements while still achieving the required field homogeneity through pre-computed compensation currents applied during the imaging process.
Solution Approach 2:
The patent changes the operational parameters of the shim coils by using temporally variable currents instead of constant currents. The system dynamically adjusts the shim coil current parameters during the imaging sequence based on pre-calculated compensation values, enabling simpler magnet designs to achieve the necessary field homogeneity without requiring complex multi-element superconducting magnets.
2Manufacturing precision
If superconducting magnets with many coil elements are used to achieve high field homogeneity, then the polarization field homogeneity is improved, but the helium consumption increases
Solution Approach 1:
The system performs preliminary calculation of field inhomogeneity compensation parameters before imaging, storing these values for later use. This approach enables the use of simpler magnets with fewer superconducting coils, directly reducing the amount of helium required for cooling while maintaining the necessary field homogeneity through software-based compensation.
Solution Approach 2:
The patent replaces expensive, resource-intensive permanent magnet designs with a more economical approach using temporary, software-controlled shim coil compensation. This substitution reduces reliance on large superconducting magnet systems that consume significant helium, achieving cost and resource efficiency without sacrificing imaging quality.
3Manufacturing precision
If the magnet opening is made small to provide a homogenous polarization field, then the field homogeneity is improved, but the patient comfort deteriorates
Solution Approach 1:
The system pre-calculates compensation currents for shim coils that can correct field inhomogeneities in larger, more open magnet configurations. This allows the magnet opening to be enlarged for patient comfort while maintaining field homogeneity through software-based compensation applied during imaging sequences.
Solution Approach 2:
The patent changes the approach from relying on physical magnet geometry to achieving homogeneity through dynamic parameter adjustment of shim coil currents. This enables larger magnet openings that improve patient comfort and accessibility while maintaining the necessary field homogeneity through electronically controlled compensation.
4Manufacturing precision
If constant shim coil currents are used to compensate for field inhomogeneity, then the field homogeneity is improved, but the ability to adapt to different imaging sequences is reduced
Solution Approach 1:
The patent transforms the static, constant shim coil current system into a dynamic system that can vary currents temporally during different phases of the imaging sequence. The system calculates and applies different compensation current values at different time points, enabling adaptation to various imaging sequences and protocols while maintaining field homogeneity throughout the imaging process.
Solution Approach 2:
The system implements periodic recalculation and adjustment of shim coil currents during the imaging sequence, synchronizing compensation with the periodic nature of MR imaging pulses and gradients. This allows the system to maintain optimal field homogeneity across different imaging sequences by periodically updating compensation parameters based on the specific sequence requirements.
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 enables the use of MR systems with higher intrinsic field inhomogeneities, reducing manufacturing costs and improving patient comfort by allowing for more open designs, while achieving significant reduction in field inhomogeneity through pulsed gradients, from millitesla to microtesla levels, during the imaging sequence.
Implementation Method 1
a magnet to generate a polarization field B0 that has a first field inhomogeneity across a measurement field
Implementation Method 2
The compensation magnetic field gradient is furthermore activated during a compensation time period that is shorter than the total duration of the imaging sequence, such that the first field homogeneity is reduced to a second, lower field inhomogeneity across the measurement field during the compensation time period
Data Source
AI summary
In order to detect a magnetic resonance (MR) signal in an examination region of an examination subject in a measurement field of an MR system with an MR imaging sequence, a magnetization in the examination subject is generated with a polarization field B0. The MR system has a magnet to generate the polarization field B0 with a first field inhomogeneity across the measurement field. At least one RF pulse is radiated into the examination region. At least one first magnetic field gradient is activated for spatial coding of the MR signal. At least one pulsed compensation magnetic field gradient is activated that is generated by a temporally variable current that varies over the duration of the MR imaging sequence and that is activated over a compensation time period that is shorter than the total duration of the imaging sequence so that, during the compensation time period, the first field inhomogeneity is reduced to a second, lower field inhomogeneity across the measurement field.