Velocity-Selective Arterial Spin Labeling for MRI Perfusion
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Solution Overview
Problem
Arterial spin labeling (ASL) techniques in MRI are spatially selective, leading to transit delays in delivering tagged blood to target tissues, causing errors in cerebral blood flow quantitation, especially in clinical applications like stroke, due to variations in delivery time along the vascular tree.
Innovation Solution
Velocity selective ASL (VS-ASL) uses velocity-selective RF pulses to tag all flowing spins regardless of location, reducing transit delays and allowing for non-spatially dependent tagging, enabling improved perfusion quantification by acquiring images with and without velocity-selective tagging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spatially selective tagging is used in ASL, then the tagging can be applied to a specific plane or slab close to the target tissue, but this causes transit delays in delivering tagged blood to the target tissues
Solution Approach 1:
The patent changes the selection parameter from spatial (location-based) to velocity-based. Instead of selecting spins based on their spatial position in a slab, the invention selects spins based on their flow velocity using velocity-selective RF pulses combined with gradient fields. This allows tagging of all arterial blood regardless of location, eliminating the transit delay problem while maintaining selective tagging of flowing blood.
Solution Approach 2:
The patent introduces velocity as an additional dimension for spin selection beyond the traditional spatial dimension. By using velocity-selective RF pulses with gradient fields, the system creates a tagging mechanism that operates in velocity space rather than purely in spatial space, allowing simultaneous tagging of all spatial locations that share the same velocity characteristics.
2Measurement precision
If spatially selective tagging is used, then the tagging can be confined to a defined region, but variations in delivery time along the vascular tree cause errors in cerebral blood flow quantitation
Solution Approach 1:
The patent fundamentally changes the tagging selection parameter from spatial coordinates to velocity magnitude. This allows uniform tagging of all arterial blood flowing through the imaging volume regardless of their distance from the tagging location or path length variations. The velocity-selective approach ensures that all tagged spins represent arterial blood with similar flow characteristics, improving the reliability of CBF quantitation.
Solution Approach 2:
The velocity-selective tagging mechanism serves multiple functions simultaneously: it tags all arterial blood regardless of location, selects based on flow velocity characteristics, and provides uniform tagging across the entire imaging volume. This universal tagging approach eliminates the need for multiple spatially selective slabs and improves measurement reliability.
3Ease of manufacture
If pulsed ASL techniques are used with spatial selectivity, then a slab of tissue containing arterial blood can be tagged, but this approach is susceptible to delivery time related artifacts
Solution Approach 1:
The patent maintains the simplicity of pulsed tagging by using discrete RF pulse sequences but changes the selection criterion from spatial to velocity-based. The velocity-selective RF pulses are applied in a pulsed manner similar to conventional ASL, preserving the ease of implementation while eliminating delivery time artifacts through velocity-based rather than location-based selection.
Solution Approach 2:
The patent replaces the mechanical/spatial selection mechanism (defining a physical slab or plane in space) with a velocity-based selection mechanism using RF pulse frequency and gradient field combinations. This substitution eliminates the inherent spatial constraints and associated delivery time variations while maintaining the pulsed tagging approach.
4Ease of manufacture
If continuous ASL techniques are used with spatial selectivity, then blood flowing through a defined plane can be tagged, but this approach is also susceptible to delivery time related artifacts
Solution Approach 1:
The patent changes the continuous tagging mechanism from spatially selective to velocity-selective. Instead of continuously tagging blood passing through a defined spatial plane, the invention uses continuous velocity-selective RF pulsing that tags all arterial blood based on flow velocity. This eliminates delivery time artifacts while maintaining the continuous tagging advantage of uniform temporal sampling.
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
VS-ASL reduces delivery delays and improves perfusion quantification accuracy, making it suitable for various clinical applications, including stroke, by ensuring consistent tagging across the brain and eliminating spatial selectivity-related artifacts.
Implementation Method 1
an RF pulse train is applied to selectively tag spins according to velocities of the spins without selection based on locations of the spins
Implementation Method 2
gradient fields along mutually orthogonal x, y, or z directions in a xyz coordinate system to spatially select a body part for imaging, and an RF magnetic field (B1) to manipulate the spins
Implementation Method 3
a static magnetic field along a z-direction to polarize the magnetic spins of hydrogen atoms in the body part
Data Source
AI summary
Techniques for providing velocity-selective magnetic arterial spin labeling in magnetic resonance imaging (MRI) without spatial selectivity. In one implementation, an RF pulse train is applied to selectively tag spins according to velocities of the spins without selection based on locations of the spins. MRI images of tagged spins at an area of interest are then acquired to obtain information on perfusion at the area of interest.