MRI T1 and T2 Relaxation Mapping via Dual-Echo SSFP Sequences
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Solution Overview
Problem
Current MRI protocols for 3D T1 and T2 relaxometry require multiple sequences, leading to long acquisition times and susceptibility to patient movement, and existing methods fail to account for T2* bias effects, resulting in artefacts and errors in relaxation time mapping.
Innovation Solution
A method using a combination of SSFP-FID and dual-echo SSFP sequences to acquire 2D or 3D MRI images, allowing for the determination of T1 and T2 values from two acquisitions by eliminating T2* dependence and using numerical inversion methods to generate accurate relaxation time maps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple MRI sequences are acquired for 3D T1 and T2 relaxometry, then measurement precision is improved, but loss of time increases and reliability deteriorates due to patient movement
Solution Approach 1:
The patent combines T1 and T2 mapping into a single dual-echo SSFP acquisition sequence, where the first echo provides T1-weighted information and the second echo provides T2-weighted information. This merging of multiple sequences into one eliminates the need for separate acquisitions, reducing total scan time while maintaining measurement precision through simultaneous multi-contrast data collection.
Solution Approach 2:
The patent employs periodic RF excitation pulses with specific timing (TR/2) to generate steady-state signals that encode both T1 and T2 relaxation information. By using periodic excitation with optimized timing, the sequence efficiently extracts multiple relaxation parameters within a single repetition cycle, minimizing acquisition time while preserving measurement accuracy.
2Measurement precision
If multiple MRI sequences are acquired for 3D T1 and T2 relaxometry, then measurement precision is improved, but reliability deteriorates due to patient movement affecting image registration
Solution Approach 1:
The patent acquires all necessary T1 and T2 mapping data within a single continuous dual-echo SSFP sequence, eliminating gaps between separate acquisitions. This ensures that all images are obtained under identical patient positioning and anatomical conditions, guaranteeing perfect spatial registration without requiring post-processing alignment algorithms.
3Productivity
If TrueFISP sequence is used for T1 mapping, then productivity is improved, but measurement precision deteriorates due to banding artefacts
Solution Approach 1:
The patent extracts only the necessary signal information from the SSFP sequence by using dual-echo acquisition with specific timing. By selecting signals at TR/2 and utilizing the first and second echoes separately, the method extracts pure T1 and T2 relaxation information while eliminating the banding artefacts that plague conventional SSFP T1 mapping, maintaining both speed and precision.
4Productivity
If DESS sequence is used for T2 estimation, then productivity is improved, but measurement precision deteriorates due to T2* bias effects
Solution Approach 1:
The patent extracts pure T2 relaxation information by utilizing the second echo signal from the dual-echo SSFP sequence, which is acquired at a later time point where T2* effects have decayed. This extraction of T2-weighted signal at optimized timing eliminates T2* bias while maintaining the fast acquisition characteristics of steady-state sequences.
Solution Approach 2:
The patent changes the echo time parameter to TR/2 for the second echo, optimizing the timing to minimize T2* contamination while maximizing T2 contrast. By adjusting this temporal parameter, the sequence achieves accurate T2 measurement without the speed penalty of conventional multi-echo sequences.
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 reduces acquisition time, minimizes artefacts, and provides high-quality T1, T2, and T2p maps with improved signal-to-noise ratio, enabling better detection of focal alterations in tissues like cartilage.
Implementation Method 1
MRI (Magnetic Resonance Imaging) is a non-invasive imaging instrument which uses the magnetic properties of the nuclei of certain atoms, in particular of hydrogen protons
Implementation Method 2
a first MRI image acquired using a SSFP-FID (Steady State Free Precession - Free Induction Decay) acquisition sequence
Data Source
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AI summary
A method for generating 2D or 3D maps of MRI T1 and T2 relaxation times by acquiring 2D or 3D MRI gradient-echo images and extracting the T1 and T2 values from said images, wherein MRI images are acquired using a combination of gradient-echo sequences, including: a first MRI image acquired using a SSFP-FID (Steady State Free Precession - Free Induction Decay) acquisition sequence; two further images acquired using a Dual-Echo SSFP acquisition sequence; the T1 and T2 values are extracted for each image pixel or voxel from the corresponding MRI signals.