Phase Contrast MRA Background Suppression via Temporal Flow Encoding
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Solution Overview
Problem
Current magnetic resonance angiography (MRA) techniques, particularly phase contrast MRA, require acquiring two separate data sets for image subtraction, leading to increased acquisition time and artifacts due to gradient-induced eddy currents and background phase shifts, which negatively impact temporal resolution and accuracy.
Innovation Solution
A method and system for MRA that utilize phase-based flow encoding, allowing for the collection of a time-series of image data and identifying periods of reduced flow to subtract background tissue, thereby suppressing background tissue and improving image quality without the need for dual data acquisitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two separate data sets are acquired for phase contrast MRA image subtraction, then background tissue suppression is achieved, but acquisition time is doubled and temporal resolution is reduced
Solution Approach 1:
The patent applies periodic action by acquiring multiple images over time during a single data set, using temporal fluctuations in blood flow to create moving and stationary components. Instead of acquiring two separate static data sets, the system captures a time series of images where blood flow varies periodically, allowing background suppression through temporal subtraction of images acquired at different phases of the cardiac cycle.
Solution Approach 2:
The patent uses preliminary action by acquiring a reference image during a period of reduced or absent blood flow before the main imaging sequence. This reference image, containing primarily background tissue, is subtracted from subsequent images to suppress background signals. The preliminary acquisition of flow-free reference data enables efficient background removal without requiring a complete second data set.
2Measurement precision
If two separate data sets are acquired with different gradient waveforms, then flow encoding is achieved, but gradient-induced eddy currents and background phase shifts increase
Solution Approach 1:
The patent applies parameter changes by varying the timing and amplitude of gradient pulses within a single data set acquisition, rather than using different gradient waveforms across two separate data sets. The gradient parameters are adjusted temporalally to encode flow information while maintaining consistent hardware conditions, thereby reducing eddy currents and background phase shifts that arise from waveform differences between separate acquisitions.
Solution Approach 2:
The patent merges the acquisition of flow-encoded images and background reference images into a single data set. By combining multiple imaging acquisitions with different gradient timings into one continuous scan, the system eliminates the need for separate data set acquisitions with different waveforms, thereby reducing gradient-induced artifacts while maintaining flow encoding capability.
3Measurement precision
If contrast agents such as gadolinium are used for CE MRA, then diagnostic capability is enhanced, but cost increases and nephrogenic systemic fibrosis risk is introduced
Solution Approach 1:
The patent applies self-service by using the patient's own blood flow dynamics as the contrast mechanism. Instead of introducing external contrast agents, the system exploits the natural temporal variations in blood flow velocity and volume to generate contrast between flowing blood and stationary tissue. The blood flow itself serves as the contrast source, eliminating the need for gadolinium or other contrast agents and their associated risks.
Solution Approach 2:
The patent substitutes the chemical contrast mechanism (gadolinium-based contrast agents) with a physical/physiological mechanism (temporal flow variations). By replacing chemical contrast enhancement with physical flow encoding through gradient pulses and temporal subtraction, the system achieves diagnostic capability without introducing harmful contrast agents.
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 enhances temporal resolution by half, reduces echo time, and minimizes gradient-induced artifacts, resulting in more accurate and efficient MRA imaging with reduced background phase corrections.
Implementation Method 1
phase-based flow encoding
Implementation Method 2
nuclear magnetic resonance (NMR) phenomenon
Implementation Method 3
precess about it in random order at their characteristic Larmor frequency
Implementation Method 4
magnetic field gradients (Gx, Gy, and Gz) are employed
Implementation Method 5
applying gradient pairs, which sequentially dephase and then rephase spins during the sequence
Implementation Method 6
radiofrequency (RF) field which is in the x-y plane and which is near the Larmor frequency
Implementation Method 7
the signal which is emitted by the excited spins after the excitation field B1 is terminated
Implementation Method 8
gradient-induced eddy currents are not identical for the two acquisitions, which results in spatially and time-varying background phase shifts
Data Source
AI summary
A system and method is provided for magnetic resonance angiography (MRA) that includes performing a pulse sequence using the MRI system, the pulse sequence including a phase-based flow encoding to collect a time-series of image data from the portion of the vasculature of the subject and identifying at least a portion of the time series of image data corresponding to a period of reduced flow through the portion of the vasculature. The portion of the time series of image data is subtracted from the time series of image data to create a time series of images of the portion of the vasculature having background tissue surrounding the portion of the vasculature substantially suppressed.