Non-Contrast MR Angiography Using Variable Flip Angle Echo Trains
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Solution Overview
Problem
Current non-contrast agent MR angiography techniques face challenges in achieving high-resolution imaging within short acquisition times and low Specific Absorption Rate (SAR) on high-field systems, while effectively separating arteries from veins without contrast agents.
Innovation Solution
The method employs ECG or pulse-triggered half Fourier turbo spin echo acquisition with variable flip angle evolution, utilizing a 90° excitation pulse followed by refocus pulses of less than 180°, and subtractive imaging techniques to create high-resolution 2D maximum intensity projections from 3D volume data sets acquired at different cardiac phases, optimizing cardiac phase and spoil gradients for systole and diastole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional non-contrast MR angiography techniques are used, then imaging can be performed without contrast agents, but acquisition time is long and resolution is insufficient
Solution Approach 1:
The imaging process is divided into multiple cardiac phase acquisitions (systole and diastole) with different trigger delay times. By segmenting the acquisition into multiple phases and using subtraction imaging, the method achieves high resolution while maintaining short total acquisition time through parallel processing of different cardiac phases
Solution Approach 2:
The method dynamically adjusts trigger delay times to capture different cardiac phases (systole and diastole). By making the acquisition dynamic and adaptive to the cardiac cycle, the system optimizes imaging resolution at each phase while maintaining overall acquisition speed through the dynamic nature of cardiac gating
2Reliability
If conventional MR angiography is used, then vessels can be visualized, but Specific Absorption Rate (SAR) is high on high-field systems
Solution Approach 1:
The method changes the RF pulse parameters by using variable flip angle refocus pulses (smaller than or equal to 180°) instead of conventional large flip angles. This parameter change reduces the Specific Absorption Rate while maintaining imaging quality and vessel visualization through optimized pulse sequences
3Measurement precision
If arteries and veins are not effectively separated, then imaging is simpler, but diagnostic accuracy is reduced
Solution Approach 1:
The method segments the imaging process into multiple cardiac phase acquisitions (systole and diastole) and uses subtraction imaging to separate arteries from veins. By dividing the acquisition into phases and using mathematical subtraction, the system achieves effective vessel separation without requiring overly complex hardware
Solution Approach 2:
The method uses feedback from multiple acquisitions at different trigger delay times to identify and separate arterial and venous signals. By analyzing the signal characteristics across different cardiac phases and using this feedback information, the system accurately separates vessels while managing sequence complexity through algorithmic processing
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 faster acquisition with reduced SAR, sharper MR angiography images, and improved separation of arteries from veins, suitable for high-field imaging within safety guidelines, while minimizing motion artifacts and acquisition time.
Implementation Method 1
magnetic resonance imaging method for non-contrast imaging of blood
Implementation Method 2
turbo spin echo based acquisition with variable flip angle evolution
Implementation Method 3
electrocardiograph or pulse triggered half fourier turbo spin echo-based acquisition
Implementation Method 4
From the third 3D volume data set a 2D substantially maximum intensity projection data set is created which may then be displayed to show the blood at the region
Data Source
AI summary
In a magnetic resonance imaging method for non-contrast imaging of blood at a region in the subject's body, a first 3D MR image is acquired represented by a first 3D volume data set of the region at a first trigger delay time. The first 3D image is acquired using a substantially 90° excitation pulse followed by a plurality of variable flip angle refocus pulses forming an echo train where the refocus pulses are smaller than or equal to 180°. To form the first 3D MR image, multiple MR slices are acquired related to the first trigger delay time to speed up the acquisition of the first image. A second 3D MR image is acquired represented by a second 3D volume data set at the same region using the same steps for acquiring the first 3D MR image except that a second trigger delay time is used which is different than the first trigger delay time. The first 3D volume data set and the second 3D volume data set are subtracted to create a third 3D volume data set. From the third 3D volume data set a 2D substantially maximum intensity projection data set is created which may then be displayed to show the blood at the region.