Velocity-compensated diffusion MRI gradient pulse sequence
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional magnetic resonance imaging (MRI) diffusion sequences, such as the Stejskal-Tanner sequence, suffer from reduced diffusion sensitivity due to cardiac motion artifacts, leading to overestimation of the apparent diffusion coefficient (ADC) and decreased signal-to-noise ratio (SNR), especially in applications like diffusion-weighted imaging of the liver and heart.
Innovation Solution
A speed-compensated diffusion sequence with an odd number of diffusion contrast gradient pulses is employed, where the sum of zeroth and first gradient moments are zero, allowing for improved diffusion sensitization and reduced echo time, thereby minimizing artifacts and enhancing SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If velocity-compensated bipolar gradients are used to reduce cardiac motion artifacts, then motion artifacts are reduced, but diffusion sensitivity decreases and echo time increases
Solution Approach 1:
The diffusion gradient sequence is divided into multiple smaller gradient pulses (at least three pulses) instead of using a single bipolar gradient pair. This segmentation allows the first moment to be nulled while maintaining diffusion sensitivity, as each pulse contributes to the overall diffusion weighting while the timing and amplitude are optimized to achieve velocity compensation.
Solution Approach 2:
The gradient pulse parameters (amplitude, duration, timing) are optimized to achieve both velocity compensation (M1=0) and adequate diffusion sensitivity. By adjusting these parameters, the patent achieves a balance where motion artifacts are reduced while maintaining sufficient diffusion weighting, avoiding the need to increase echo time.
2Measurement precision
If gradient duration is increased to achieve desired diffusion sensitivity with velocity-compensated sequences, then diffusion sensitivity improves, but echo time and acquisition time increase
Solution Approach 1:
By segmenting the diffusion gradient into multiple pulses, the patent achieves diffusion sensitivity without requiring a single long gradient duration. The cumulative effect of multiple shorter pulses provides adequate diffusion weighting while keeping the overall echo time shorter than conventional velocity-compensated sequences.
3Measurement precision
If Stejskal-Tanner sequence is used for diffusion-weighted imaging, then diffusion sensitivity is maintained, but cardiac motion artifacts increase leading to ADC overestimation
Solution Approach 1:
The patent applies velocity compensation (first moment nulling) to the diffusion gradient sequence before the imaging process. This preliminary anti-action counteracts the effects of cardiac motion, preventing the phase errors that would otherwise lead to ADC overestimation and signal loss, while maintaining the diffusion sensitivity of the Stejskal-Tanner sequence.
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 achieves higher diffusion sensitivity in a shorter time, reducing echo time and minimizing artifacts from macroscopic motion, resulting in improved image quality and diagnostic accuracy.
Implementation Method 1
defined magnetic field gradients are superimposed on the basic magnetic field during the transmission and reading or receiving of the high-frequency signals
Implementation Method 2
the nuclear spins of certain atoms, which are resonantly excited by this high-frequency field within the given magnetic field
Implementation Method 3
Diffusion refers to the Brownian motion of molecules in a medium
Implementation Method 4
Diffusion refers to the Brownian motion of molecules in a medium
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A method for controlling a magnetic resonance imaging system to generate magnetic resonance image data of a subject is described, in which raw magnetic resonance data is acquired. The method includes an excitation process in which an excitation RF pulse is generated. Furthermore, the method includes a readout process for receiving RF signals. Additionally, the method generates a diffusion contrast gradient pulse sequence, wherein the diffusion contrast gradient pulse sequence comprises an odd number of 2n+1 temporally sequential diffusion contrast gradient pulses, where the sum of the zeroth gradient moments of the diffusion contrast gradient pulses is zero, and the sum of the first gradient moments of the diffusion contrast gradient pulses is zero. An RF refocusing pulse is inserted between two of the diffusion contrast gradient pulses.A control sequence for controlling a magnetic resonance imaging system is also described. Furthermore, a control sequence determination system is also described. Additionally, a magnetic resonance imaging system is also described.