Spatially Encoded Phase-Contrast MRI for Fast 3D Imaging
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Solution Overview
Problem
Conventional MRI techniques face challenges in achieving fast acquisition times for 3D imaging without compromising image quality, particularly due to geometric distortions, signal losses, and increased radiofrequency power absorption, which hinder real-time monitoring of dynamic processes.
Innovation Solution
The method employs spatially encoded phase-contrast MRI, utilizing at least two settings of spatially encoding phase-contrast gradients to calculate the mean spin density position of an object along a selected spatial dimension, significantly reducing the number of required MR signal acquisitions, from 256 to just two 2D acquisitions, thereby accelerating the 3D data collection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional MRI techniques are used for 3D imaging, then image quality can be maintained, but acquisition time is excessively long (more than 100 times slower than the invention)
Solution Approach 1:
The invention extracts only the essential information needed for 3D localization (mean spin density position along one spatial dimension) from the full 3D imaging process. By using phase-contrast gradients to encode spatial position in the third dimension and calculating the mean position from two 2D acquisitions, the method extracts sufficient 3D localization data without requiring complete 3D spatial encoding, thus dramatically reducing acquisition time while maintaining adequate image quality for dynamic process monitoring
Solution Approach 2:
The invention changes the encoding parameter from full spatial resolution in all three dimensions to phase-contrast encoding along one dimension. By applying phase-contrast gradients with different gradient moments (first-order for velocity encoding, second-order for spatial position encoding), the method transforms the imaging approach to acquire spatial position information through phase differences rather than through complete spatial sampling, reducing acquisition time by more than 100-fold
2Loss of time
If single-shot gradient-echo sequences are used for high-speed acquisition, then acquisition time is reduced, but geometric distortions and signal losses occur due to sensitivity to off-resonance effects
Solution Approach 1:
The invention uses periodic RF pulsing with gradient application in a controlled sequence, where phase-contrast gradients are applied periodically with specific gradient moments. The method employs periodic excitation with defined gradient waveforms that refocus spins at specific times, creating a periodic pattern of signal acquisition that is less sensitive to off-resonance effects compared to single-shot sequences, thereby maintaining image quality while achieving fast acquisition
Solution Approach 2:
The invention applies preliminary phase-contrast encoding gradients before signal acquisition to pre-establish the phase information needed for spatial localization. By encoding the spatial position information in the phase of the MR signal through preliminary gradient application, the method prepares the signal in advance to be less sensitive to subsequent off-resonance effects and field inhomogeneities during the actual readout
3Reliability
If single-shot sequences with radiofrequency-refocused spin echoes are used, then geometric distortions are avoided, but radiofrequency power absorption increases with risk of local tissue heating
Solution Approach 1:
The invention applies partial RF refocusing by using low-flip-angle RF pulses instead of complete 180-degree refocusing pulses. The phase-contrast encoding is achieved with gradient moments rather than requiring full RF refocusing, thus obtaining the necessary spatial and velocity information with reduced RF power deposition, lowering the risk of local tissue heating while maintaining adequate signal quality
4Productivity
If single-shot sequences are used for real-time imaging, then acquisition speed is improved, but the frame rate remains insufficient for practical real-time monitoring
Solution Approach 1:
The invention segments the 3D imaging process into two separate 2D acquisitions with different phase-contrast gradient settings. Instead of attempting to acquire complete 3D data in a single shot, the method divides the task into sequential 2D acquisitions that can be performed rapidly, then combines them through phase difference calculation to reconstruct 3D information, achieving a practical frame rate for real-time monitoring
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 reduces the total acquisition time by more than a factor of 100, enabling continuous 3D MR image acquisition with high temporal resolution and maintaining image quality, allowing for real-time imaging of dynamic processes with a practical frame rate.
Implementation Method 1
spatially encoding phase-contrast gradients differently encoding the phase of said MR signals
Implementation Method 2
subjecting the object to at least one RF pulse and magnetic field gradients for creating spatially encoded MR signals
Data Source
AI summary
A method of collecting magnetic resonance data for imaging an object with a predetermined spin density being arranged in a static magnetic field, comprises the steps subjecting said object to at least one radiofrequency pulse and magnetic field gradients for creating spatially encoded magnetic resonance signals, including at least two settings of spatially encoding phase-contrast gradients differently encoding the phase of said magnetic resonance signals in at least one field of view in a predetermined spatial dimension, acquiring at least two magnetic resonance signals, each with one of said at least two settings of different spatially encoding phase-contrast gradients, and determining at least one mean spin density position of said object along said spatial dimension by calculating the phase difference between said signals. Furthermore, a control device and a magnetic resonance imaging (MRI) device implementing the method are described.