Real-Time MR Shim Current Adjustment for Organ Motion
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Solution Overview
Problem
Existing magnetic resonance (MR) imaging technologies face challenges in achieving optimal magnetic field homogeneity, particularly for organs with irregular shapes or those that change during acquisition, such as the heart or liver, leading to unsatisfactory signal and image quality.
Innovation Solution
Measuring physiological characteristics, like cardiac or respiratory signals, to determine shim currents for improving magnetic field homogeneity, using a separate measurement device and optimizing shim currents in real-time during MR data acquisition, allowing for flexible and focused shimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional shimming methods are used with fixed rectangular acquisition windows, then magnetic field homogeneity is improved for regular shapes, but image quality deteriorates for organs with irregular shapes or those that change shape during acquisition
Solution Approach 1:
The patent applies dynamics by making the shimming system adaptive to changing physiological states. The system dynamically adjusts shimming parameters based on real-time detection of organ position and shape changes during the acquisition process, transforming a static shimming approach into a dynamic one that can accommodate moving and irregularly-shaped organs like the heart and liver.
Solution Approach 2:
The patent implements parameter changes by modifying the shimming parameters (such as shim coil currents and field correction coefficients) based on detected organ characteristics. The system changes these parameters in response to varying organ positions and shapes throughout the acquisition, allowing optimal field homogeneity to be maintained despite physiological movements.
2Manufacturing precision
If multiple field maps are acquired to improve shimming accuracy for moving organs, then magnetic field homogeneity is improved, but acquisition time and cost increase
Solution Approach 1:
The patent implements continuity of useful action by performing shimming updates continuously or periodically during the acquisition process rather than requiring multiple separate field map acquisitions. The system maintains continuous monitoring of organ position and continuously adjusts shimming parameters, eliminating the need for repeated time-consuming field map measurements while maintaining accurate shimming throughout the scan.
Solution Approach 2:
The patent applies feedback by using real-time detection of organ position and shape to continuously inform and adjust the shimming parameters. The system creates a feedback loop where organ movement information is immediately used to correct field inhomogeneities, eliminating the need for multiple preliminary field map acquisitions and reducing total acquisition time while maintaining shimming accuracy.
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 enhances MR image quality by dynamically adjusting shim currents based on the subject's internal state, reducing the need for additional field maps and enabling real-time imaging, thus improving diagnostic data acquisition efficiency and reducing costs.
Implementation Method 1
the shim coil is driven with the shim current
Implementation Method 2
use shim coils to reduce the inhomogeneities and improve the homogeneity of the main magnetic field
Implementation Method 3
a physiological characteristic of the subject is measured and used to determine the shim current
Data Source
Figure 1~2
AI summary
In summary, a novel method to shim a magnetic field inside an MR apparatus (2) is described as well as an advantageous MR arrangement (1) that may be used to perform the novel method. For the shimming, that can also be done in real-time, a physiological characteristic (14) of the subject (9) is measured and used to determine optimal shim currents. The method works with standard pre-installed shim systems, but is particularly beneficial for local multi-coil shim inserts (4).