3D Oscillating Gradient MRI Sequence for Short Diffusion Time
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Solution Overview
Problem
Current oscillating gradient diffusion magnetic resonance imaging (OG-dMRI) techniques face limitations in clinical applications due to the need for strong diffusion gradients, leading to limited short diffusion time, low contrast-noise ratio, and increased acquisition time, especially in 2D multislice acquisitions, which result in system heating and longer repetition times.
Innovation Solution
The introduction of a 3D oscillating-gradient prepared gradient spin-echo sequence (OGprep-GRASE) that includes a global saturation module, diffusion preparation module with trapezoidal cosine oscillation gradients, fat saturation, and multiplexed sensitivity-encoding reconstruction, allowing for improved diffusion encoding and signal acquisition in 3D k-space, thereby enhancing the signal-to-noise ratio and reducing scan time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If oscillating gradient dMRI is used to achieve shorter diffusion time, then diffusion time is reduced, but the b value is limited to 300-500 s/mm2 and contrast-noise ratio decreases
Solution Approach 1:
The patent divides the diffusion encoding process into two separate modules: an oscillating gradient module for diffusion time control and a spin echo module for signal acquisition. This segmentation allows independent optimization of each module, enabling short diffusion times while maintaining high b values and contrast-noise ratios through the dedicated spin echo readout.
Solution Approach 2:
The spin echo module acts as an intermediary between the oscillating gradient diffusion encoding and the final signal acquisition. It transfers the diffusion-encoded magnetization to the k-space domain with high fidelity, preserving the contrast information while enabling flexible readout parameters that maintain signal quality.
2Measurement precision
If strong oscillation gradient is applied to achieve reasonable b value on clinical scanner, then b value is achieved, but echo time increases and signal-to-noise ratio decreases
Solution Approach 1:
The patent separates diffusion encoding from signal acquisition into distinct modules. The oscillating gradient module applies strong gradients for adequate b values while the spin echo module uses optimized echo train lengths and flip angles to maintain high signal-to-noise ratio, allowing independent optimization of each function.
Solution Approach 2:
The patent employs variable flip angle schedules in the spin echo module and adjusts echo train lengths to optimize the balance between b value achievement and signal preservation. By dynamically changing acquisition parameters, it maintains high signal-to-noise ratio even with strong oscillating gradients.
3Quantity of substance
If 2D multislice acquisition is performed with repeated strong oscillation gradient, then all slices are acquired, but duty cycle increases and system heating occurs
Solution Approach 1:
The patent transitions from 2D slice-by-slice acquisition to 3D volumetric acquisition using the spin echo module. This dimensional change allows simultaneous encoding of multiple slices in the third dimension (z-direction), reducing the need for repeated strong oscillating gradients and thereby decreasing duty cycle and system heating.
Solution Approach 2:
The 3D spin echo readout enables continuous data acquisition across multiple slices without requiring repeated application of the oscillating gradient between slices. This continuous action reduces the total time the high-power gradients are active, lowering duty cycle and thermal load on the gradient system.
4Loss of time
If 2D-EPI based OG-dMRI is used for acquisition, then imaging is performed, but scan time is long and signal-to-noise ratio is low
Solution Approach 1:
The patent segments the acquisition into an oscillating gradient preparation module for compact diffusion encoding and a spin echo readout module for efficient signal acquisition. This segmentation allows the use of longer echo trains in the spin echo module without sacrificing diffusion time, thereby reducing scan time while maintaining or improving signal-to-noise ratio through optimized echo spacing and flip angles.
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
The 3D OGprep-GRASE sequence effectively shortens scan time and improves the signal-to-noise ratio compared to conventional 2D-EPI based OG-dMRI, demonstrating clear diffusion time dependence in human brain imaging and providing reliable diffusion coefficient measurements.
Implementation Method 1
The oscillation gradient is composed of multiple periodic cosine or trapezoidal cosine waveforms, which has been successfully used to study the time-dependent dMRI of animals and water models on animal MRI systems
Implementation Method 2
embedding a pair of trapezoidal cosine oscillation gradients or pulse gradients into a 90°x-180°y-90°−x radiofrequency pulses to achieve the separation of diffusion encoding from signal acquisition
Implementation Method 3
adding a diffusion preparation module after post-saturation delay (PSD), and embedding a pair of trapezoidal cosine oscillation gradients or pulse gradients into a 90°x-180°y-90°−x radiofrequency pulses
Implementation Method 4
adding a global saturation module at the beginning of a sequence to destroy previous residual transverse magnetization
Implementation Method 5
adding a fat saturation module after the diffusion preparation module to suppress fat signals
Data Source
AI summary
A method for 3D oscillating-gradient prepared gradient spin-echo imaging and a device. The imaging method comprises the following steps: first, using a global saturation module to destroy previous residual transverse magnetization; second, embedding a pair of trapezoidal cosine oscillating gradients into a 90°x-180°y-90°−x radiofrequency pulse by a diffusion encoding module, to separate diffusion encoding from signal acquisition; then, using a fat saturation module to suppress a fat signal; finally, acquiring a signal by means of gradient spin-echo readout, and correcting phase errors among multiple excitations by multiplexed sensitivity-encoding reconstruction. Compared with a 2D plane echo-based oscillating gradient diffusion sequence used on a 3T clinical system, a 3D oscillating-gradient prepared gradient spin-echo sequence effectively reduces the imaging time, improves the signal to noise ratio, and is beneficial to clinical transformation of time-dependent diffusion MRI technology.