Non-contrast MRA Using Segmented 2D Slices and Flow Compensation
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Solution Overview
Problem
Current non-contrast enhanced magnetic resonance angiography (MRA) techniques face limitations such as sensitivity to patient motion, inadequate vessel anatomy portrayal, excessively long scan times, and poor depiction of slowly flowing arterial spins, particularly in patients with severe vascular disease, due to limitations in existing methods like phase contrast and time-of-flight imaging.
Innovation Solution
A method utilizing a series of two-dimensional imaging slices and corresponding tagging slices with non-Cartesian acquisition to generate dynamic or static MR angiographic images, allowing for improved spatial resolution and reduced scan time by labeling flowing spins and reconstructing time-series images of vascular structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If non-contrast enhanced MRA techniques (phase contrast or time-of-flight) are used, then contrast agents are avoided, but scan times become excessively long and image quality deteriorates
Solution Approach 1:
The imaging volume is divided into multiple thin 2D slices acquired sequentially. Each slice is imaged independently using a balanced SSFP sequence with flow compensation, allowing for rapid acquisition while maintaining high spatial resolution. This segmentation enables the scan time to be reduced from what would be required for a single 3D non-contrast MRA acquisition.
Solution Approach 2:
The patent employs a balanced steady-state free precession (bSSFP) sequence with specific parameter optimization including flow compensation gradients and tailored repetition times. These parameter changes enable the sequence to be both rapid (reducing scan time) and sensitive to flowing blood (maintaining image quality without contrast agents).
2Loss of time
If single shot acquisition methods like 2D balanced steady-state free precession are used, then motion artifacts are reduced and exam times are shortened, but arterial conspicuity is inadequate due to high background signal
Solution Approach 1:
Flow compensation gradients are applied before the imaging pulse to pre-compensate for the phase effects of flowing blood. This preliminary action ensures that moving spins remain in-phase during the acquisition window, enhancing arterial signal intensity and conspicuity against the background before the actual imaging occurs.
Solution Approach 2:
The patent acquires multiple copies of k-space data at different temporal points during the cardiac cycle. By combining these temporal copies through a technique called temporal combining, the method reconstructs images with enhanced arterial conspicuity that would not be achievable from a single shot acquisition alone.
3Object-affected harmful factors
If existing non-contrast MRA methods are used, then contrast agents are not required, but vessel anatomy is not accurately portrayed in patients with severe vascular disease
Solution Approach 1:
Flow compensation gradients are applied before the imaging pulse to pre-compensate for the phase effects of flowing blood. This preliminary action ensures that moving spins remain in-phase during the acquisition window, enhancing arterial signal intensity and conspicuity against the background before the actual imaging occurs.
Solution Approach 2:
The patent employs a balanced steady-state free precession (bSSFP) sequence with specific parameter optimization including flow compensation gradients and tailored repetition times. These parameter changes enable the sequence to be both rapid (reducing scan time) and sensitive to flowing blood (maintaining image quality without contrast agents).
4Quantity of substance
If traditional MRA sequences are used, then vascular imaging is achieved, but slowly flowing arterial spins are not adequately depicted
Solution Approach 1:
Flow compensation gradients are applied before the imaging pulse to pre-compensate for the phase effects of flowing blood. This preliminary action ensures that moving spins remain in-phase during the acquisition window, enhancing arterial signal intensity and conspicuity against the background before the actual imaging occurs.
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 the production of high spatial resolution, dynamic MR angiographic images depicting blood flow within vessels, overcoming the limitations of existing methods by reducing scan time and improving image quality, particularly in patients with severe vascular disease.
Implementation Method 1
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the nuclear spins in the tissue attempt to align with this polarizing field, but process about it in random order at their characteristic Larmor frequency. If, however, the substance, or tissue, is subjected to a magnetic field (excitation field B1; also referred to as the radiofrequency (RF) field) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, Mz, may be rotated, or 'tipped' into the x-y plane to produce a net transverse magnetic moment Mt, which is rotating, or spinning, in the x-y plane at the Larmor frequency. The practical value of this phenomenon resides in the signal which is emitted by the excited spins after the excitation field B1 is terminated.
Implementation Method 2
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged experiences a sequence of measurement cycles in which these gradients vary according to the particular localization method being used.
Data Source
AI summary
A method for non-contrast enhanced magnetic resonance angiography (MRA) of a three-dimensional (3D) volume of a subject having a vascular structure extending through the 3D volume and having flowing spins passing through vascular structure. The method includes applying at least one radiofrequency (RF) pulse to a first slice to label the flowing spins passing into a second slice located within the 3D volume adjacent to the first slice and acquiring imaging data from the second slice using a two-dimensional (2D) pulse sequence and sampling k-space using a non-Cartesian sampling pattern. The acquisition of the of the imaging data is repeated to acquire a series of second slices located across the 3D volume to acquire respective sets of imaging data spanning the 3D volume. The sets of imaging data is reconstructed into a time-series of image frames depicting the flowing spins passing through the vascular structure.