Diffusion-Modulated T2 MRI Pulse Sequence for Stroke Imaging
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Solution Overview
Problem
Current MRI systems require multiple lengthy and repetitive imaging studies to acquire information about various MR parameters, such as T1 relaxation times, T2 relaxation times, and diffusion information, which is impractical and costly, especially in urgent clinical settings like acute stroke diagnosis, due to limitations in spatial resolution and heterogeneous tissue characteristics.
Innovation Solution
A system and method that combines MRI pulse sequences to sensitize T2 acquisitions to diffusion parameters, generating diffusion-modulated T2-weighted MR images and parametric maps, allowing for the acquisition of multiple MR parameters in a single imaging session by superimposing diffusion gradients on spin echo T2 MRI acquisitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If multiple separate MR acquisitions are performed to obtain different contrast mechanisms (T1, T2, diffusion), then comprehensive information about heterogeneous tissue is obtained, but the imaging time and cost increase significantly
Solution Approach 1:
The patent combines multiple MR pulse sequences (T1-weighted, T2-weighted, and diffusion-weighted sequences) into a single integrated acquisition protocol. This merging allows simultaneous collection of multiple contrast mechanisms during one imaging session, directly resolving the contradiction by obtaining comprehensive tissue information without proportionally increasing imaging time
Solution Approach 2:
The integrated pulse sequence design enables the MRI system to perform multiple diagnostic functions within a single acquisition. The sequence can generate T1-weighted images, T2-weighted images, and diffusion-weighted images with ADC calculations all from one protocol, making the imaging system universally capable of assessing various tissue properties simultaneously
2Loss of information
If multiple separate MR acquisitions are performed to obtain different contrast mechanisms, then comprehensive information about heterogeneous tissue is obtained, but the cost and complexity of the imaging protocol increase
Solution Approach 1:
The patent merges multiple imaging protocols into a single integrated sequence that automatically coordinates the acquisition of T1, T2, and diffusion-weighted data. This consolidation reduces the operational complexity for clinicians while maintaining comprehensive diagnostic information
Solution Approach 2:
The integrated sequence is designed with modular segments that can be independently configured for different tissue types and clinical indications. This segmentation allows the complex protocol to be broken down into manageable components while maintaining overall functionality
3Measurement precision
If standard T2-weighted imaging is used, then the imaging protocol is simple and fast, but the image contrast and specificity to ischemic tissue are insufficient
Solution Approach 1:
The patent modifies the standard T2-weighted sequence by incorporating diffusion sensitizing gradients and adjusting timing parameters to create diffusion-modulated T2-weighted images. This parameter change enhances the sensitivity to ischemic tissue while maintaining reasonable imaging speed
Solution Approach 2:
The imaging approach combines multiple contrast mechanisms (T2 relaxation contrast plus diffusion weighting) into a composite imaging protocol. This composite approach leverages the complementary information from both mechanisms to improve ischemic tissue detection while balancing imaging efficiency
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 enables the generation of multi-MR parameter weighted images, enhancing image contrast and specificity to ischemic tissue, improving diagnosis by providing more accurate and sensitive T2 measurements, particularly in stroke imaging, while reducing the need for extensive imaging protocols.
Implementation Method 1
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the excited nuclei in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency.
Implementation Method 2
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 to produce a net transverse magnetic moment Mt.
Implementation Method 3
The amplitude, A, of the emitted NMR signal decays in an exponential fashion with time, t. The decay constant 1/T*2 depends on the homogeneity of the magnetic field and on T2, which is referred to as the 'spin-spin relaxation' constant, or the 'transverse relaxation' constant.
Implementation Method 4
Another important factor that contributes to the amplitude A of the NMR signal is referred to as the spin-lattice relaxation process that is characterized by the time constant T1. It describes the recovery of the net magnetic moment M to its equilibrium value along the axis of magnetic polarization (z).
Implementation Method 5
a so-called diffusion weighted imaging ('DWI') pulse sequence uses motion sensitizing magnetic field gradients to obtain images having contrast related to the diffusion of water or other fluid molecules. Specifically, a DWI pulse sequence applies diffusion sensitizing magnetic field gradients in selected directions during the MRI measurement cycle to obtain MR images that have an image contrast related to the diffusion of water or other fluid molecules that occurred during the application of the diffusion gradients.
Data Source
AI summary
A system and method for applying an RF excitation pulse to the region of interest (ROI) and a plurality of selective gradients to the ROI to elicit MR data pertaining to at least a first MR parameter from the ROI. The system and method also apply at least one diffusion gradient to the ROI to modulate the first MR parameter with a second MR parameter, acquire MR data from the ROI, and reconstruct a parametric map of the ROI using the MR data, wherein the parametric map is weighted based on the first MR parameter and modulated by the second MR parameter.