Quantitative MRI Parameter Mapping with Separate Proton Density Estimation
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Solution Overview
Problem
Existing quantitative magnetic resonance imaging (qMRI) methods face challenges in accurately estimating multiple parameters due to a high number of unknowns, leading to increased complexity and reduced accuracy, particularly in estimating proton density (PD), which affects the estimation of other parameters like T1 and T2.
Innovation Solution
A method that involves a separate steady-state acquisition to directly measure proton density using gradient echo sequences with low flip angles and short repetition times, followed by a transient-state acquisition to quantify other parameters, reducing the number of unknowns and improving estimation accuracy through least-squares fitting and coil sensitivity calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple parameters are estimated simultaneously in qMRI, then comprehensive tissue characterization is achieved, but the number of unknowns increases leading to reduced accuracy and increased complexity
Solution Approach 1:
The patent segments the parameter estimation process into two distinct phases: first estimating proton density (PD) from steady-state signals, then using PD as a known quantity to estimate T1 and T2 from transient-state signals. This segmentation reduces the number of unknowns in each estimation step, improving accuracy while maintaining comprehensive tissue characterization capability.
Solution Approach 2:
The patent performs preliminary estimation of proton density before estimating other parameters like T1 and T2. By obtaining PD first from steady-state acquisitions and treating it as a known quantity in subsequent transient-state analysis, the method reduces computational complexity and improves the precision of subsequent parameter estimates.
2Loss of information
If proton density is estimated along with other parameters, then complete quantitative information is obtained, but cross-talk between parameters increases reducing estimation accuracy
Solution Approach 1:
The patent separates PD estimation from T1/T2 estimation into distinct computational steps. PD is first determined from steady-state signals, then used as a fixed input for transient-state analysis. This segmentation eliminates cross-talk between parameters while preserving complete quantitative information through sequential estimation.
Solution Approach 2:
The patent performs preliminary PD measurement before transient-state parameter estimation. By establishing PD as a known quantity in advance, the method eliminates parameter cross-talk in the subsequent T1 and T2 estimation processes while maintaining complete quantitative information about tissue properties.
3Measurement precision
If steady-state acquisition with specific flip angles is used to measure PD, then PD measurement accuracy is improved, but the complexity of the acquisition sequence increases
Solution Approach 1:
The patent uses specific flip angle parameters in steady-state gradient echo sequences to optimize PD measurement accuracy. By carefully selecting flip angles that minimize T1 weighting and maximize PD sensitivity, the method achieves accurate PD measurement while using a relatively simple gradient echo sequence rather than more complex multi-pulse 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 enhances the accuracy of qMRI by directly measuring PD in a steady-state acquisition, simplifying parameter estimation and reducing cross-talk, thereby improving the conditioning of the inverse problem and facilitating more robust parameter mapping.
Implementation Method 1
Magnetic resonance imaging (MRI) is a medical imaging modality that can create images of the inside of a human body
Implementation Method 2
performing a steady-state acquisition to obtain first MR signals
Implementation Method 3
determining one or more quantitative MR parameters based on the second MR signals and the PD for that voxel
Implementation Method 4
determining one or more quantitative MR parameters based on the second MR signals and the PD for that voxel
Data Source
AI summary
Systems and methods are provided for quantitative parameter estimation for magnetic resonance (MR) imaging. In one example, a method includes performing a steady-state acquisition to obtain first MR signals of a scan volume, performing a transient-state acquisition to obtain second MR signals of the scan volume, determining, for each voxel of the scan volume, a respective proton density (PD) based on the first MR signals, determining, for each voxel of the scan volume, one or more respective quantitative MR (qMR) parameters based on the second MR signals and the PD for that voxel, and outputting one or more parameter maps for display and/or storage based on the one or more respective qMR parameters.