Bone MRI via Susceptibility Map Residual Analysis
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Solution Overview
Problem
Magnetic Resonance Imaging (MRI) struggles to effectively image bone tissue due to its short T2 time, making it difficult to detect and localize cortical bone, which is crucial for radiation treatment planning and PET image reconstruction, as conventional MRI methods fail to account for bone-induced magnetic field perturbations that do not produce a strong signal.
Innovation Solution
A medical instrument and method that utilize a magnetic resonance imaging system to calculate a subject magnetic susceptibility map, B0 inhomogeneity map, and residual B0 magnetic field perturbation map, allowing for the inference of bone tissue distribution by subtracting the susceptibility-induced perturbations from the inhomogeneity map, and applying Green's functions for iterative refinement of bone localization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MRI methods are used to image bone tissue, then the imaging process is simple and fast, but the detection precision of bone tissue is insufficient due to short T2 time and lack of signal
Solution Approach 1:
The patent uses magnetic susceptibility maps as an intermediary to indirectly detect bone tissue. Instead of attempting to directly image bone with MRI (which fails due to short T2), the method calculates susceptibility maps from surrounding tissues and uses the residual B0 field perturbations as a mediator to infer bone location and distribution.
Solution Approach 2:
The patent replaces direct MRI signal detection (mechanical/spin-based) with magnetic field perturbation analysis. By substituting the direct imaging approach with field-based susceptibility mapping and perturbation analysis, the method overcomes the fundamental limitation of bone's short T2 relaxation time.
2Measurement precision
If special pulse sequences like UTE are used to image bone tissue, then the detection precision improves, but the imaging time and complexity increase significantly
Solution Approach 1:
The patent makes the B0 field mapping serve multiple functions: it characterizes tissue susceptibility, identifies bone locations through perturbation analysis, and provides anatomical information. This multi-functional approach eliminates the need for separate specialized bone imaging sequences like UTE.
Solution Approach 2:
The method uses the existing B0 field data acquired during routine MRI scanning to simultaneously perform susceptibility mapping and bone detection. The system serves itself by utilizing already-acquired field information rather than requiring additional dedicated scanning sequences.
3Measurement precision
If image segmentation is used to detect bone borders, then the detection precision improves, but the method cannot accurately localize cortical bone and bone-induced field perturbations
Solution Approach 1:
The patent extracts the bone-induced perturbation component from the total B0 field inhomogeneity by subtracting the susceptibility-induced perturbations. This separation isolates the specific signal component related to cortical bone, which is then used to create accurate bone maps.
Solution Approach 2:
The method changes the parameter being measured from direct MRI signal intensity to B0 field perturbation magnitude and spatial distribution. By measuring field perturbations rather than signal intensity, the system can detect cortical bone that produces no direct signal.
4Productivity
If the B0 field inhomogeneity is used directly for bone localization, then the method is simple and fast, but it cannot distinguish between susceptibility-induced perturbations and bone-induced perturbations
Solution Approach 1:
The patent segments the B0 field inhomogeneity into distinct components: susceptibility-induced perturbations (calculated from tissue susceptibility maps) and bone-induced perturbations (residual after subtraction). This segmentation allows accurate attribution of field variations to specific sources.
Solution Approach 2:
The method uses an iterative feedback approach where the calculated susceptibility maps and perturbation models are continuously refined by comparing predicted and actual B0 field measurements, improving the accuracy of bone localization with each iteration.
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 localization of bone tissue within the subject, improving radiation treatment planning and PET image reconstruction by quantitatively determining the distribution of bone tissue that was previously undetectable, enhancing the accuracy of radiation attenuation maps and bone mapping.
Implementation Method 1
a main magnet for generating a B0 magnetic field within an imaging zone
Implementation Method 2
This large static magnetic field is used by Magnetic Resonance Imaging (MRI) scanners to align the nuclear spins of atoms
Implementation Method 3
Radio Frequency (RF) pulses generated by one or more transmitter coils cause a called B1 field
Implementation Method 4
RF signals are then emitted by the nuclear spins are detected by one or more receiver coils
Implementation Method 5
bone-induced magnetic field perturbations that do not produce a strong signal
Data Source
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AI summary
The invention provides for a medical instrument (100, 500) comprising a magnetic resonance imaging system (102) for acquiring magnetic resonance data (142) from a subject (118) within an imaging zone (108). The magnetic resonance imaging system comprises: a main magnet (104) for generating a B0 magnetic field within the imaging zone; a memory (134, 136) containing machine executable instructions (160, 162, 164, 166) and pulse sequence commands (140); a processor (130) for controlling the medical instrument. Execution of the machine executable instructions causes the processor to: acquire (200) the magnetic resonance data by controlling the magnetic resonance imaging system with the pulse sequence commands; receive (202) a subject magnetic susceptibility map (144) of the subject; calculate (204) a B0 inhomogeneity map (146) from the magnetic resonance data; calculate (206) a subject B0 magnetic field perturbation (148) from the subject magnetic susceptibility map; calculate (208) a residual B0 magnetic field perturbation (150) by subtracting the subject B0 magnetic field perturbation from the B0 inhomogeneity map; and calculate (210) a bone map (152) from the residual B0 magnetic field perturbation.