DESS T2 Map Estimation via Linear Echo Relationship
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Solution Overview
Problem
Current methods for estimating T2 maps in MRI using the Double-Echo Steady-State (DESS) sequence are complex and require numerical searches, making immediate and automatic parameter mapping challenging, especially for clinical scans, and often result in errors due to simplifications used in approximate models.
Innovation Solution
A simplified linear relationship between the two DESS echoes is derived using the Extended Phase Graph formalism, ignoring higher-order echo pathways that have spent more than two repetition times in the transverse plane, providing a more accurate and efficient method for T2 estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If numerical search methods are used to estimate T2 maps from DESS sequences, then measurement precision is improved, but device complexity and computational time increase significantly
Solution Approach 1:
The patent extracts and isolates the dominant signal components from the DESS sequence, separating the primary echo pathways that contribute most to T2 weighting from higher-order pathways. By focusing only on the essential signal components (ignoring pathways spending more than two TR in transverse plane), the method achieves accurate T2 estimation without requiring complex numerical searches of all possible signal pathways.
Solution Approach 2:
The patent changes the mathematical formulation from a complex numerical optimization problem to a simplified linear relationship between DESS echoes. By deriving an analytical solution based on modified signal equations that account for T1 relaxation effects, the method transforms the estimation problem into a computationally efficient calculation that maintains accuracy without requiring iterative numerical searches.
2Productivity
If simplified approximate models are used for T2 estimation, then computational time is reduced, but measurement precision deteriorates due to modeling errors
Solution Approach 1:
The patent performs preliminary derivation of the signal relationship between DESS echoes, establishing an analytical formula that incorporates T1 relaxation effects before actual T2 estimation is performed. This pre-established linear relationship allows direct calculation of T2 values without iterative optimization, achieving both computational efficiency and accuracy by eliminating the need for complex numerical searches during the estimation process.
3Measurement precision
If complete signal modeling including all echo pathways is used, then measurement precision is improved, but loss of time increases due to computational burden
Solution Approach 1:
The patent extracts and retains only the dominant echo pathways that contribute significantly to T2-weighted signal, specifically ignoring pathways that spend more than two repetition times in the transverse plane. This selective extraction maintains measurement precision by focusing on the most relevant signal components while dramatically reducing computational time by eliminating unnecessary calculations of minor pathways.
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 allows for accurate T2 estimation with reduced computational time and improved accuracy compared to existing methods, validated through simulations, phantom scans, and in vivo knee scans, with minimal sensitivity to errors in T1 estimation.
Implementation Method 1
nuclear magnetic moments are excited at specific spin precession frequencies which are proportional to the local magnetic field. The radio-frequency signals resulting from the precession of these spins are received using pickup coils.
Implementation Method 2
By manipulating the magnetic fields, an array of signals is provided representing different regions of the volume.
Implementation Method 3
each nuclear spin responds to four different effects: precession about the main magnetic field, nutation about an axis perpendicular to the main field, and both transverse and longitudinal relaxation
Implementation Method 4
each nuclear spin responds to four different effects: precession about the main magnetic field, nutation about an axis perpendicular to the main field, and both transverse and longitudinal relaxation
Data Source
AI summary
A method for providing an estimated 3D T2 map for magnetic resonance imaging using a Double-Echo Steady-State (DESS) sequence for a volume of an object in a magnetic resonance imaging (MRI) system is provided. A DESS scan of the volume is provided by the MRI system. Signals S1 and S2 are acquired by the MRI system. Signals S1 and S2 are used to provide a T2 map for a plurality of slices of the volume, comprising determining repetition time (TR), echo time (TE), flip angle α, and an estimate of the longitudinal relaxation time (T1), and wherein the DESS scan has a spoiler gradient with an amplitude G and a duration τ and ignoring echo pathways having spent more than two repetition times in the transverse plane.