Magnetic Shim Array for Selective Artery Labeling in pCASL MRI
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Solution Overview
Problem
Current arterial spin labeling (ASL) techniques, particularly pseudo-continuous ASL (pCASL), face challenges in efficiently labeling blood due to off-resonance B0 fields, which affects labeling efficiency and cannot selectively control labeling in individual arteries, leading to reduced sensitivity and increased artifactual hypoperfusion.
Innovation Solution
The use of a magnetic shim array to shim the magnetic field in the labeling plane with DC currents, creating a non-uniform magnetic field that selectively enhances or reduces labeling efficiency in specific regions, allowing for precise control over blood labeling in individual arteries, thereby improving perfusion imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform B0 field is used in the labeling plane, then the imaging volume field homogeneity is optimized, but the labeling efficiency is reduced due to off-resonance effects
Solution Approach 1:
The patent applies different field homogeneity conditions to different spatial regions: the imaging volume maintains uniform B0 field for optimal imaging, while the labeling plane introduces controlled inhomogeneity through shim coils to achieve resonance conditions and improve labeling efficiency. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The patent segments the magnetic field control into independent regions by using separate shim coils that affect only the labeling plane without disrupting the imaging volume field homogeneity. This allows independent optimization of labeling efficiency in the labeling plane while maintaining imaging quality in the brain region.
2Measurement precision
If the scanner shim prioritizes the field homogeneity of the imaging volume, then imaging quality is improved, but the field homogeneity of the labeling plane deteriorates causing off-resonance
Solution Approach 1:
The shim coil system is segmented into independent units that can be selectively activated. The patent uses specific shim coils (e.g., Z2, Z3) that are configured to affect only the labeling plane region, allowing the imaging volume to maintain optimal field homogeneity while the labeling plane receives targeted field adjustment to eliminate off-resonance effects.
Solution Approach 2:
The patent applies local field correction exclusively to the labeling plane region using positioned shim coils, leaving the imaging volume field characteristics unchanged. This localized approach improves labeling plane homogeneity without compromising imaging quality, resolving the contradiction between the two regional requirements.
3Productivity
If conventional pCASL labeling is applied to the whole labeling plane, then overall labeling is achieved, but selective control over individual arteries is lost
Solution Approach 1:
The patent creates spatially varying resonance conditions across the labeling plane by using shim coils to generate controlled B0 field inhomogeneity. This results in different labeling efficiencies in different regions of the labeling plane, enabling selective labeling of blood in specific arteries (e.g., carotid vs. vertebral) while maintaining overall labeling efficiency. Each artery territory can be selectively targeted by adjusting the shim coil currents to create appropriate field patterns.
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 labeling efficiency, achieving high sensitivity and resilience to artifactual hypoperfusion by selectively targeting specific arteries while minimizing labeling in others, providing more accurate perfusion maps without modifying the standard pCASL sequence.
Implementation Method 1
A first resulting field in the labeling plane is a non-uniform magnetic field such that the RF field labels the nuclear spin of blood in at least one artery
Implementation Method 2
pCASL uses a narrow labeling plane through which flow-related adiabatic inversion of arterial spins occurs
Implementation Method 3
magnetization of arterial blood water is inverted (i.e., 'labeled') using a long train of short, Hanning-windowed block pulses
Implementation Method 4
Perfusion-weighted color maps and relative cerebral blood flow (relCBF) color maps can be calculated
Data Source
AI summary
Systems and methods for localized pseudo-continuous ASL (pCASL) of arterial blood local multi-coil arrays in an MRI system allow a series of pulses to selectively label blood with an on-resonance magnetic field in one or more arteries in a labeling plane while masking blood in others with an off-resonance magnetic field. This allows perfusion imaging and is well suited for imaging of cerebral blood flow.