Phase-Describing Map Optimization Using Min-Cut Max-Flow
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Solution Overview
Problem
Conventional magnetic resonance imaging methods, such as the two-point Dixon method, are limited by the need for precisely defined echo times, reducing flexibility in sequence development and signal-to-noise ratio optimization, and fail to accurately handle complex chemical shifts in substances like fat and water due to assumptions of single resonance frequencies.
Innovation Solution
A method and image processing device that determine a phase-describing map using arbitrary echo times, employing a min-cut/max-flow algorithm to optimize phase values and generate accurate image data for multiple chemical substance types, allowing for flexible echo time selection and improved signal-to-noise ratio, even in conditions with no mathematically unambiguous solutions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precisely defined echo times are used in conventional magnetic resonance imaging methods, then accurate separation of chemical substance types can be achieved, but flexibility in sequence development and signal-to-noise ratio optimization is reduced
Solution Approach 1:
The patent changes the parameter of echo time from fixed predefined values to arbitrary selectable values. The system allows echo times to be chosen freely while using optimization algorithms to determine the correct phase describing map, thereby achieving both flexibility in sequence design and accurate chemical substance separation.
Solution Approach 2:
The patent introduces dynamic optimization through the min-cut/max-flow algorithm that adapts to arbitrary echo times. Instead of relying on static predefined echo times, the system dynamically determines phase values based on the actual echo times used, enabling flexible sequence development while maintaining separation accuracy.
2Adaptability or versatility
If arbitrary echo times are used to increase flexibility, then sequence development and signal-to-noise ratio optimization improve, but accurate handling of chemical shifts becomes more difficult
Solution Approach 1:
The patent uses feedback through optimization algorithms that take the actual arbitrary echo times as input and adjust the phase describing map accordingly. The min-cut/max-flow algorithm receives feedback from the measured signal data and iteratively determines the correct phase values, ensuring accurate chemical substance separation despite arbitrary echo time selection.
Solution Approach 2:
The patent performs preliminary determination of candidate phase values before final image reconstruction. By pre-calculating possible phase values and using optimization to select the correct ones, the system prepares the necessary corrections in advance, enabling accurate separation even with arbitrary echo times.
3Device complexity
If conventional methods assume single resonance frequencies for substances, then calculations are simplified, but complex chemical shifts in substances like fat and water are not accurately handled
Solution Approach 1:
The patent segments the complex chemical substance separation problem into determining individual phase values for each pixel independently. By treating each pixel's phase determination as a separate optimization problem using min-cut/max-flow, the system can handle complex chemical shifts accurately without requiring simplified single-frequency assumptions.
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
The method provides robust and stable image separation for fat and water, reducing phase wraps and inconsistencies, and allows for optimized magnetic resonance sequence design, achieving high accuracy and flexibility in image generation.
Implementation Method 1
These radio-frequency pulses excite the spins of the nuclei, in general hydrogen nuclei, in the object under investigation such that they are deflected by an 'excitation flip angle' from their equilibrium position parallel to the basic magnetic field B0. The nuclear spins precess initially around the z-direction and gradually relax again
Implementation Method 2
the excited nuclei in the body tissue have no uniform resonance frequency in the magnetic field. Rather, the resonance frequency can differ for different tissue types or substance types depending on their chemical environment. This is commonly known as chemical shift
Implementation Method 3
The spatial encoding of the received signals takes place with the use of rapidly switched gradient magnetic fields, which are overlaid on the basic magnetic field during the transmission of the magnetic resonance radio frequency pulses and/or the acquisition of the raw data
Data Source
AI summary
In a method and apparatus for generating a phase-describing map in a firm that is usable to generate magnetic resonance (MR) image data, first and second sets of magnetic resonance echo raw data are acquired from a region of the examination subject, at two different echo times, said first and second sets of magnetic resonance echo raw data originating from two different chemical substance types. First and second image data sets of the defined region are reconstructed respectively from the first and second sets of magnetic resonance echo raw data. An energy function is determined that contains at least one term that places phase-describing values of map points of a phase-describing map in relation to each other dependent on a difference of the respective phase-describing values of the respective map points. The energy function is optimized to obtain an optimized phase-describing map.