Selective MRI Angiography Using Flow-Dependent Subtraction
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Solution Overview
Problem
Current magnetic resonance angiography (MRA) techniques face challenges in selectively imaging arteries and veins without contrast agents, particularly due to overlapping projective images and the intermittent nature of venous flow, which limits diagnostic utility and exposes patients to safety risks.
Innovation Solution
A system and method for non-enhanced MRA that uses a combination of RF saturation pulses and quiescent inflow time periods to acquire flow-dependent and flow-independent imaging data sets, allowing for subtraction to selectively depict arteries or veins with improved contrast and reduced risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contrast-enhanced MRA is used to evaluate vascular disease, then arterial imaging quality is improved, but venous imaging is compromised due to overlap from arteries and requires costly blood pool agents
Solution Approach 1:
The patent segments the vascular imaging into separate arterial and venous components by applying directionally-selective saturation pulses. Arterial spins are saturated from one direction while venous spins are saturated from the opposite direction, allowing independent imaging of each vascular bed without contrast agents or overlap
Solution Approach 2:
The patent applies different saturation conditions to different spatial locations and flow directions. By positioning saturation pulses upstream of the imaging slice and orienting them perpendicular to the main imaging slice, the method creates location-specific magnetization suppression that distinguishes arterial from venous flow based on their different flow directions
2Object-affected harmful factors
If non-enhanced MRA techniques like QISS are used, then patient safety is improved by avoiding contrast agents, but venous imaging reliability deteriorates due to intermittent venous flow
Solution Approach 1:
The patent employs dynamic flow-dependent imaging with quiescent inflow time periods that adapt to the intermittent nature of venous flow. By adjusting the timing of saturation pulses and imaging acquisition to match the dynamic flow patterns, the method reliably captures venous anatomy even when flow is absent for extended periods
Solution Approach 2:
The patent changes the flow dependency parameter by using flow-dependent saturation techniques where the degree of saturation depends on flow velocity and direction. This allows the imaging to adapt to varying flow conditions, capturing venous structures reliably without requiring continuous flow or contrast enhancement
3Productivity
If flow-independent MRA is used to image during steady-state, then imaging speed is improved, but arterial and venous images overlap severely limiting diagnostic utility
Solution Approach 1:
The patent applies preliminary saturation pulses to selectively suppress magnetization of arterial or venous spins before the main imaging acquisition. By pre-saturating spins in the direction of arterial flow or venous flow, the method ensures that only the desired vascular type contributes signal during the steady-state imaging, preventing overlap while maintaining imaging speed
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
Enables effective, non-contrast-enhanced imaging of arteries and veins, overcoming the limitations of existing techniques by providing clear, selective images of vascular structures without the need for exogenous contrast agents, even in regions with absent venous flow.
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
Implementation Method 2
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
Implementation Method 3
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 4
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed
Data Source
AI summary
A system and method for producing an image of a vascular structure of a subject using a magnetic resonance imaging (MRI) system includes performing a first pulse sequence to acquire a flow-dependent imaging data set from the stack of prescribed imaging slices following a first quiescent inflow time period (QITP). The process also includes performing a second pulse sequence without suppressing signal from spins flowing into the stack of prescribed imaging slices through either of the veins or arteries to acquire a flow-independent imaging data set. The flow-dependent imaging data and the flow-independent imaging data are subtracted to create a difference image of the stack of prescribed imaging slices illustrating the at least one of the arteries and the veins as having a bright contrast and another of the arteries and veins as having a suppressed contrast.