Magnetic Particle Imaging Calibration Volume Segmentation
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Solution Overview
Problem
In magnetic particle imaging (MPI), existing methods generate artefacts in images due to magnetic particles outside the measurement volume contributing to the signal, especially in in vivo recordings with high particle densities, leading to unreliable data.
Innovation Solution
The method involves selecting a calibration volume larger than the measurement volume, detecting calibration signals outside the measurement volume, and discarding magnetic particle concentration values associated with voxels outside the measurement volume to minimize artefacts and ensure reliable data by projecting particle signals to the outer border of the measurement volume, thus excluding their influence from the MPI image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If magnetic particles are located outside the measurement volume, then the signal contribution increases, but image artefacts increase and data reliability decreases
Solution Approach 1:
The patent divides the calibration space into two distinct segments: a measurement volume (first calibration region) and an extended calibration volume (second calibration region). By segmenting the calibration process into these two regions, the method can separately handle particles within the measurement volume versus those outside it, preventing external particles from contaminating the measurement signal while still accounting for their presence through the extended calibration volume.
Solution Approach 2:
The extended calibration volume acts as an intermediary region that mediates between the measurement volume and the surrounding space containing external magnetic particles. This intermediary calibration region allows the system to characterize and compensate for signals originating from particles outside the measurement volume, thereby protecting the integrity of the actual measurement data.
2Loss of time
If calibration is performed only within the measurement volume, then calibration time is reduced, but image artefacts increase due to unaccounted external particles
Solution Approach 1:
The patent performs preliminary calibration actions by acquiring calibration signals from both the measurement volume and the extended calibration volume before actual measurements. This preliminary characterization of the extended calibration region allows the system to pre-compute correction factors or system matrices that account for external particles, eliminating the need for time-consuming iterative corrections during actual measurements while preventing artefact generation.
3Reliability
If the calibration volume is extended beyond the measurement volume, then coverage of external particles is improved, but system complexity increases
Solution Approach 1:
The patent applies local quality by using different calibration strategies for different spatial regions: within the measurement volume, full-resolution calibration is performed, while in the extended calibration volume, a coarser or simplified calibration approach is used. This localized differentiation allows comprehensive particle coverage without uniformly increasing system complexity across the entire calibration space.
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 results in low-artefact image data with high magnetic particle densities outside the measurement volume, improving data reliability and reducing calibration and reconstruction time, particularly beneficial for in vivo recordings.
Implementation Method 1
the magnetic particles are exposed to different static and dynamic magnetic fields in a measurement volume and the magnetization changes of the magnetic particles are detected by means of receiver coils
Implementation Method 2
A magnetic gradient field is applied in the region of the measurement volume which has a field-free region. The field-free region is shifted along a pre-defined trajectory (predetermined dependence of each point of the field-free region) within the measurement volume by means of a dynamic magnetic field (drive field) and/or homogeneous focus fields
Data Source
AI summary
An MPI method determines calibration and measurement volumes, wherein the calibration volume is larger than the measurement volume and the overall measurement volume is arranged within the calibration volume. Calibration signals are detected and a system matrix S is created. An MPI measuring signal u is recorded, a location-dependent magnetic particle concentration c with magnetic particle concentration values ci within the calibration volume is reconstructed and the magnetic particle concentration values ci are associated with voxels in the calibration volume. Magnetic particle concentration values ci which were associated with voxels outside of the measurement volume are discarded and an MPI image is generated which exclusively contains magnetic particle concentration values ci which were associated with the voxels within the measurement volume. MPI image data are thereby generated with little artifacts within a short time even in case of high magnetic particle densities outside of the measurement volume.