Tensor Elastography Imaging Using Cardiac Pulsation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional elastography techniques struggle to accurately characterize anisotropic tissues like the brain, heart, and other organs due to the ill-posed nature of reconstructing the rank-4 anisotropic elasticity tensor, and the challenges of transmitting mechanical energy through bony structures and high wave attenuation, limiting the characterization of mechanical anisotropy.
Innovation Solution
The method employs spin echo MRI and ultrasound to measure small physiological tissue displacements, reconstructs a full rank-4 anisotropic elasticity tensor using denoised displacement fields, and applies physically motivated compatibility conditions and invariant stains to characterize tissue properties without external actuation, leveraging cardiac pulsation or other physiological motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional elastography techniques use external actuators to generate shear waves for tissue characterization, then mechanical energy can be transmitted into the tissue, but the energy is largely reflected due to impedance mismatch at the bone-tissue interface and attenuated by tissue dissipation, requiring large tamper amplitudes that could preclude certain patient cohorts
Solution Approach 1:
The patent utilizes the heart's own physiological motion (cardiac pulsation) as the mechanical excitation source instead of external actuators. The heart naturally generates mechanical energy that deforms adjacent brain tissue, eliminating the need for external energy transmission through the skull and avoiding impedance mismatch issues entirely.
Solution Approach 2:
The patent uses the skull as a natural amplifier rather than a barrier. The cardiac pulsation energy is amplified by the skull structure (Monroe-Kellie doctrine) to produce sufficient tissue deformation, converting what was previously a harmful reflective interface into a beneficial amplifying intermediary.
2Loss of time
If high frequency mechanical excitation is used to reduce MR echo time with oscillating displacement encoding gradients, then the imaging time can be reduced, but the energy transmitted into the tissue is further dampened due to dissipation within the tissue which typically increases with increasing frequency
Solution Approach 1:
The patent changes the frequency parameter from high frequency (conventional MRE) to low frequency (physiological cardiac pulsation, approximately 1 Hz). This parameter change reduces tissue energy dissipation while still enabling effective tissue deformation for measurement, accepting longer measurement times in exchange for reduced energy loss.
3Measurement precision
If the full rank-4 anisotropic elasticity tensor is reconstructed from a single mechanical excitation, then the complete E-tensor can be obtained, but the problem is ill-posed since the number of unknowns typically exceeds the number of available equations
Solution Approach 1:
The patent measures all components of the displacement field (three spatial components) in response to a single mechanical excitation. This excessive measurement of displacement components provides sufficient equations to solve for the multiple unknowns in the rank-4 elasticity tensor, making the previously ill-posed problem solvable.
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, non-invasive characterization of anisotropic tissues by reconstructing the full elasticity tensor, providing quantitative biomarkers for disease and trauma assessment, and overcoming limitations of conventional methods.
Implementation Method 1
spin echo MRI and ultrasound to measure small physiological tissue displacements
Implementation Method 2
spin echo MRI and ultrasound to measure small physiological tissue displacements
Implementation Method 3
leveraging cardiac pulsation or other physiological motion
Data Source
AI summary
Magnetic resonance and ultrasound methods can produce estimates of full rank-4 elasticity tensors (E-tensors) using suitable constraints. E-tensor estimates can be based on E-tensor symmetry conditions and a suitable E-tensor selected from among a set of E-tensors calculated using different symmetry constraints. Displacement fields used in E-tensor calculations can be noise reduced using compatibility conditions. With the selected E-tensor, various stains that are rotation invariant can be computed. In one example, an E-tensor for an in vivo brain is computed using the mechanical disturbance associated with cardiac pulsations. The selected E-tensor and associated stains, physiological disorders such as Alzheimer's disease and traumatic brain injury (TBI) and even neural activation may be more readily detected than with conventional methods that do not use the full E-tensor.