Diffusion Encoding Sequence for Motion-Compensated MRI
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Solution Overview
Problem
Current diffusion-weighted magnetic resonance imaging (dMRI) methods struggle to accurately measure tissue microstructure in moving organs due to bulk motion, which causes signal dropout and artifacts, limiting their effectiveness in applications like imaging the heart.
Innovation Solution
A method involving a diffusion encoding sequence with a time-dependent magnetic field gradient having non-zero components along orthogonal directions and a b-tensor with multiple non-zero eigenvalues, using two encoding blocks to adapt and compensate for motion, allowing for planar, ellipsoidal, or spherical encoding while minimizing sensitivity to velocity and acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current b-tensor encoding schemes are used for diffusion weighted magnetic resonance measurements, then specificity to microstructural features is improved, but signal dropout and artifacts occur due to bulk motion of the sample
Solution Approach 1:
The patent applies preliminary anti-action by designing a diffusion encoding sequence that proactively compensates for bulk motion effects before they degrade the measurement. The sequence includes gradient moments that are specifically engineered to counteract the effects of sample motion, thereby preventing signal dropout and artifacts rather than correcting them after they occur.
Solution Approach 2:
The patent utilizes parameter changes by modifying the diffusion encoding sequence parameters, specifically the gradient moments, to be insensitive to bulk motion. By adjusting the timing and amplitude parameters of the magnetic field gradients, the sequence maintains sensitivity to molecular diffusion while becoming robust against macroscopic sample movement.
2Loss of information
If multidimensional diffusion encoding is applied to moving organs, then tissue microstructure information is obtained, but bulk motion causes signal dropout and image artifacts
Solution Approach 1:
The patent converts the harmful effect of bulk motion into a beneficial outcome by designing gradient moments that exploit the motion characteristics. Instead of treating motion purely as a disturbance, the sequence is engineered so that the gradient moments naturally compensate for motion effects, turning the previously harmful bulk motion into a condition that does not degrade image quality.
3Measurement precision
If diffusion encoding sequence with multiple non-zero eigenvalues is used, then sensitivity to compartment anisotropy is improved, but sensitivity to velocity and acceleration increases
Solution Approach 1:
The patent applies segmentation by dividing the diffusion encoding sequence into distinct gradient lobes with specific moment characteristics. By segmenting the encoding into multiple gradient pulses with carefully controlled areas and timings, the sequence achieves multidimensional diffusion encoding while the individual segments are designed to cancel out sensitivity to velocity and acceleration effects.
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 precise diffusion-weighted magnetic resonance measurements even in the presence of bulk motion, reducing signal artifacts and improving the accuracy of tissue microstructure analysis in moving organs by effectively compensating for motion-related distortions.
Implementation Method 1
operating a magnetic resonance scanner to apply a diffusion encoding sequence to the sample; wherein the diffusion encoding sequence comprises a diffusion encoding time-dependent magnetic field gradient with non-zero components along at least two orthogonal directions
Implementation Method 2
Diffusion encoding magnetic field gradients allow MR measurements to be sensitized for diffusion, which in turn can be used to infer information about tissue microstructure
Implementation Method 3
operating the magnetic resonance scanner to acquire from the sample one or more echo signals
Data Source
AI summary
A system and method for diffusion weighted magnetic resonance measurement includes performing a diffusion encoding sequence that comprises a diffusion encoding time-dependent magnetic field gradient g(t) with non-zero components gl(t) along two orthogonal directions (y, z), and a b-tensor having at least two non-zero eigenvalues. The gradient g(t) comprises a first and second encoding block. An n-th order gradient moment magnitude along direction l∈(y,z) is given by |Mnl(t)|=∫0tgl(t′)t′ndt′|, and the first encoding block is adapted to yield, at an end of the first encoding block, along y, |Mny(t)|≤Tn for each 0≤n≤m, where Tn is a predetermined n-th order threshold, and, along z, |Mnz(t)|≤Tn for each 0≤ n≤ m−1 and |Mnz(t)|>Tn for n=m. The second encoding block is adapted to yield, at an end of the second encoding block, along each one of l∈(y,z): |Mnl(t)|≤Tn for each 0≤n≤ m, wherein m is an integer order equal to or greater than 1.