RF Phase Modulation for Single-Acquisition T2 Mapping
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Solution Overview
Problem
Current MRI techniques for generating quantitative maps, such as T2 mapping, face challenges including extended acquisition times and susceptibility to motion artifacts, particularly in methods like dual-echo steady-state (DESS) that require multiple acquisitions and are prone to inaccuracy due to signal complexity and diffusion encoding.
Innovation Solution
A phase-based approach using RF phase modulation in a gradient echo pulse sequence that induces a phase difference between echoes at different echo times, allowing for the derivation of a B0 map and subsequent T2 mapping with a single acquisition, reducing the risk of misregistration and artifact errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple acquisitions are performed to generate quantitative maps (e.g., T2 mapping), then measurement precision is improved, but loss of time increases due to extended acquisition times
Solution Approach 1:
The patent combines multiple contrast mechanisms (T1, T2, and diffusion weighting) into a single acquisition using a unified pulse sequence with phase modulation. This merging eliminates the need for separate acquisitions for each parameter, thereby reducing total acquisition time while maintaining measurement precision through the integrated design of the sequence that captures all necessary signal information in one go.
Solution Approach 2:
The pulse sequence implements continuous phase modulation throughout the acquisition process, allowing uninterrupted data collection for multiple parameters simultaneously. The continuous encoding of T2 and diffusion information into the phase of the MR signal enables seamless acquisition without requiring interruption for multiple separate scans, thus reducing time loss while preserving precision.
2Measurement precision
If multiple acquisitions are performed for quantitative mapping, then measurement precision is improved, but reliability deteriorates due to motion artifacts and misregistration
Solution Approach 1:
By merging all necessary measurements into a single continuous acquisition, the patent eliminates the gaps between scans where patient motion can occur. The unified pulse sequence captures T1, T2, and diffusion information simultaneously, preventing misregistration artifacts that arise from comparing data acquired at different times, thereby improving reliability while maintaining precision.
Solution Approach 2:
The pulse sequence incorporates preliminary phase modulation encoding during the acquisition process itself, rather than requiring post-processing alignment of multiple scans. By pre-encoding the necessary phase information within the single acquisition window, the method prevents motion-induced misregistration, enhancing reliability without compromising measurement precision.
3Measurement precision
If complex pulse sequences with diffusion encoding are used, then measurement precision for quantitative maps is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex mechanical or temporal sequencing of multiple acquisitions with a unified phase modulation approach. Instead of using separate pulse sequences for different parameters, the invention encodes all information (T1, T2, diffusion) into the phase domain through systematic phase modulation, simplifying the overall system architecture while maintaining high measurement precision.
Solution Approach 2:
The invention changes the encoding parameter from separate magnitude-based acquisitions to unified phase-based encoding. By modulating the phase of the MR signal according to T2 and diffusion parameters within a single sequence, the method reduces device complexity while preserving measurement precision through efficient use of the phase dimension for information encoding.
4Measurement precision
If signal weighting is optimized for specific contrast mechanisms, then measurement precision for that mechanism is improved, but loss of information increases regarding other contrast mechanisms
Solution Approach 1:
The pulse sequence is designed with universal applicability to extract multiple contrast mechanisms (T1, T2, diffusion) simultaneously through phase modulation. The same sequence and acquired signal serve multiple functions, enabling precise measurement of any desired parameter while retaining information about all other parameters in the phase data, thus eliminating information loss while maintaining precision for each specific mechanism.
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 method enables faster and more accurate T2 mapping with reduced artifacts, providing efficient quantitative maps without the need for multiple acquisitions, improving the reliability of T2 measurements and reducing scan time.
Implementation Method 1
magnetic field gradients (Gx, Gy, and Gz) are employed
Implementation Method 2
precess about it in random order at their characteristic Larmor frequency
Implementation Method 3
If the substance, or tissue, is subjected to a magnetic field (excitation field B1) that is in the x-y plane and that is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped', into the x-y plane
Implementation Method 4
A signal is emitted by the excited nuclei or 'spins', after the excitation signal B1 is terminated
Data Source
AI summary
A system and method are provided for producing at least one of an image or a map of a subject includes controlling a magnetic resonance imaging (MRI) system to perform a pulse sequence that includes a phase increment of an RF pulse selected to induce a phase difference between two echoes at different echo times (TE). The method also includes controlling the MRI system to acquire MR data corresponding to at least the two echoes at different TEs, deriving a static magnetic field (B0) map of the MRI system using the MR data corresponding to the two echoes, and using the B0 map and MR data from at least one of the two echoes, generate a map of T2 of the subject.