Spin-Lock RF Trains Simplify Tissue Parameter Quantification
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Solution Overview
Problem
The maximum duration of spin-lock RF pulses in MRI systems is limited by hardware and SAR, complicating the quantification of tissue parameters using a train of spin-lock RF pulses, which requires a more complex relaxation model than conventional mono-exponential models.
Innovation Solution
A method and apparatus for quantitative MRI using spin-lock radio frequency trains, involving obtaining multiple magnetization signals from trains of spin-lock modules, allowing for the simplification of quantification through a mono-exponential model by subtracting magnetization equations, and utilizing machine learning or deep learning for tissue parameter calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a train of spin-lock RF pulses is used to extend the effective spin-lock duration, then the ability to probe tissue parameters is improved, but the quantification complexity increases due to the need for complex relaxation models
Solution Approach 1:
The spin-lock train is divided into multiple individual spin-lock RF pulses with short durations. Each pulse is separated by a time interval, allowing the use of simple mono-exponential relaxation models for each segment while achieving an extended effective spin-lock duration through the cumulative effect of the train.
Solution Approach 2:
The invention changes the parameters of the spin-lock sequence by using multiple short-duration pulses instead of a single long-duration pulse. By adjusting the number of pulses, their individual durations, and the time intervals between them, the effective spin-lock duration is extended while maintaining compatibility with simple quantification models.
2Measurement precision
If the spin-lock RF pulse duration is extended to improve tissue parameter quantification, then measurement precision is improved, but SAR limits and hardware constraints are exceeded
Solution Approach 1:
The long spin-lock duration is segmented into multiple short pulses, each well within SAR and hardware limits. The cumulative effect of the pulse train achieves the desired long effective spin-lock duration for improved measurement precision while individual pulses remain safe and hardware-compatible.
Solution Approach 2:
The spin-lock train employs periodic application of short RF pulses with specific time intervals between them. This periodic action allows the magnetization to partially relax between pulses, reducing the instantaneous SAR burden while accumulating the desired spin-lock effect over the extended duration of the train.
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 quantification of tissue parameters, particularly macromolecule proton fraction, by simplifying the quantification process and enhancing sensitivity to specific tissue parameters using spin-lock RF trains.
Implementation Method 1
Spin-lock is achieved by applying a radiofrequency (RF) pulse to the magnetization to align the magnetization along an effective spin-lock field. The resulting MR signal decays with a time constant T1ρ that is related to an amplitude of the effective spin-lock field dependent on the amplitude of spin-lock pulse (γB1/2π) and the resonance frequency offset of spin-lock pulse.
Implementation Method 2
it is based on the exchange or the transfer of saturated biological molecule protons or bond water protons of macromolecules with free water protons, which are saturated by applying a selective off-resonance RF pulse. This effect results in water signal attenuation
Data Source
AI summary
A method for quantitative magnetic resonance imaging (MRI), an apparatus, and a non-transitory computer-readable storage medium are provided. In the method, a first magnetization signal is obtained based on a first train of spin-lock modules. Additionally, a second magnetization signal is obtained based on a second train of spin-lock modules. A final magnetization is obtained based on the first magnetization signal and the second magnetization signal. These processes are repeated to collect one or more final magnetization signals for quantification of tissue parameters.