Magnetic Field Measurement Using Segmented Sampling
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Solution Overview
Problem
Conventional magnetic field measurement techniques in magnetic resonance imaging are inadequate for highly inhomogeneous fields, requiring a higher number of measuring points and coefficients to achieve accurate calibration and modeling, especially outside standard field of views, leading to increased costs and longer measurement times.
Innovation Solution
A method and apparatus using a uniformly distributed sampling pattern with a bidirectional distribution of measuring points on a spherical surface, employing solid harmonics for magnetic field modeling, allowing for accurate measurement and extrapolation beyond the nominal field of view, and utilizing a carrier surface with multiple magnetic field sensors to reduce measurement time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional magnetic field measurement techniques are used with discrete measuring points on a spherical surface, then magnetic field calibration can be performed, but the number of measuring points and coefficients must be increased to achieve accurate calibration for highly inhomogeneous fields outside standard field of view
Solution Approach 1:
The measuring surface is segmented into multiple zones (first zone, second zone, third zone) with different sampling densities. The first zone near the isocenter uses a first sampling pattern, while the second and third zones at larger distances use different sampling patterns with higher density. This segmentation allows accurate measurement of inhomogeneous fields without uniformly increasing the number of measuring points throughout the entire surface.
Solution Approach 2:
Different regions of the measuring surface are assigned different measurement qualities and sampling densities based on their distance from the isocenter. The sampling pattern is adapted locally to match the expected field inhomogeneity at each position, providing higher measurement precision where needed (at the edges) and lower precision where the field is more homogeneous (near the center).
2Measurement precision
If the number of measuring points is increased to improve calibration accuracy for extended field of view, then measurement precision improves, but measurement time increases
Solution Approach 1:
The measuring surface is divided into multiple zones with different sampling densities. The first zone near the isocenter uses a coarser sampling pattern, while the second and third zones at larger distances use denser sampling patterns. This allows the measurement system to focus computational and temporal resources on the regions that require higher precision, reducing overall measurement time while maintaining calibration accuracy for extended field of view.
Solution Approach 2:
Instead of uniformly sampling the entire measuring surface at high density, the system applies partial high-density sampling only to the second and third zones where field inhomogeneity is most significant. The first zone uses lower sampling density, providing sufficient calibration accuracy with reduced measurement time in regions where high precision is less critical.
3Ease of operation
If uniform sampling pattern is used on the entire measuring surface, then measurement process is simplified, but accuracy is reduced at the edges of the field of view where inhomogeneity is stronger
Solution Approach 1:
The measuring surface is segmented into multiple zones with different sampling patterns. The first zone near the isocenter uses a first sampling pattern, while the second and third zones at larger distances use different sampling patterns with higher density. This segmentation maintains operational simplicity through automated zone-based selection while significantly improving edge field accuracy where inhomogeneity is strongest.
Solution Approach 2:
The sampling density is made non-uniform across different regions of the measuring surface, with higher density allocated to the second and third zones at the edges where field inhomogeneity is strongest. This local adaptation of sampling quality maintains measurement process simplicity through automated selection while providing the enhanced accuracy needed at critical edge regions.
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
Enables accurate calibration and modeling of inhomogeneous magnetic fields with a reduced number of measuring acts, improving image quality and extending the field of view without increasing costs or measurement time significantly.
Implementation Method 1
measuring sensor data describing the magnetic field at a plurality of measuring points on a measuring surface enclosing at least part of the field of view
Implementation Method 2
magnetic field decomposition may take place using harmonic functions, in particular solid harmonics, which are also referred to as solid spherical harmonics (SSH)
Data Source
AI summary
A method for measuring a magnetic field in a field of view of a magnetic resonance facility includes: providing a measuring apparatus including at least one magnetic field sensor; measuring sensor data describing the magnetic field at a plurality of measuring points on a measuring surface enclosing at least part of the field of view; and ascertaining magnetic field information, which models the magnetic field three-dimensionally, at least within the field of view, from the sensor data, wherein the measuring points are selected in a uniformly distributed sampling pattern for uniform sampling of the entire measuring surface.