MRI Field Map Reconstruction Using Reduced WASSR Sampling
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Solution Overview
Problem
Current Magnetic Resonance Imaging (MRI) techniques face challenges in accurately and efficiently reconstructing field maps, particularly in determining absolute water saturation frequencies, which are crucial for techniques like Chemical Exchange Saturation Transfer (CEST) imaging, due to the long data acquisition times of existing methods such as WASSR.
Innovation Solution
A medical imaging system and method that combines a reference scan for B0 field mapping with a reduced WASSR data acquisition to determine local absolute water saturation frequencies, allowing for faster and more accurate field map reconstruction by using a predefined limited set of sample points with close to zero resonance offset, and interpolating or extrapolating frequency offsets to create a high-resolution absolute frequency map.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If WASSR data acquisition is used to determine absolute water saturation frequencies, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent segments the field map determination process into two distinct parts: (1) a rapid B0 reference scan that provides relative frequency information across all voxels, and (2) a reduced WASSR scan that acquires data from only a limited number of sample points to determine absolute frequency offsets. This segmentation allows each part to be optimized independently - the reference scan for speed and the WASSR scan for precision - thereby resolving the contradiction between measurement precision and time loss.
Solution Approach 2:
The patent applies partial action by performing WASSR data acquisition at only a limited number of sample points (e.g., 2-5 points) rather than the full set of points required for complete WASSR scanning. This partial sampling is sufficient to determine the absolute frequency offset when combined with the reference scan data, significantly reducing acquisition time while maintaining the precision needed for accurate field map determination.
2Productivity
If a reduced set of sample points is used in WASSR scan, then productivity is improved, but measurement precision may deteriorate
Solution Approach 1:
The patent merges the results from two different data acquisition methods - the B0 reference scan and the reduced WASSR scan - to produce the final field map. The reference scan provides relative frequency information with high spatial coverage, while the reduced WASSR scan provides absolute frequency calibration. By combining these complementary data sources, the patent achieves both high productivity (from the reduced sampling) and maintained measurement precision (from the calibration 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 hybrid approach significantly speeds up field map data acquisition and reconstruction, providing accurate absolute frequency information for each voxel, which is essential for CEST imaging and other MRI applications, while maintaining the accuracy of WASSR methods.
Implementation Method 1
A large static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms
Implementation Method 2
Various NMR spectrographic techniques can also be used spatially
Implementation Method 3
A saturation pulse can be used to suppress the MRI signal from the exchangeable protons of the metabolites
Data Source
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AI summary
The invention provides for a medical imaging system (100, 300). The medical imaging system (100, 300) comprises a processor (104). Execution of machine executable instructions(120)causes the processor (104) to: receive magnetic resonance data, wherein the magnetic resonance datacomprises B0 field data (122) of a reference scan for a plurality of voxels and water saturation data (124) of a WASSR scan for a subset of voxels of the plurality of voxels, the water saturation data (124) comprising data of a limited number of sample points; determine a local absolute water saturation frequency (130) for each voxel of the subset using the water saturation data (124) of the WASSR scan; and reconstruct a field map (132) comprising a local absolute water saturation frequency for each voxel of the plurality of voxels, wherein the reconstruction comprises determining relative frequency differences between the voxels using the B0 field data (122) of the reference scan and adding a frequency offset to the relative frequency differences based on the determined local absolute water saturation frequencies (130) of the subset.