Susceptibility Contrast Imaging of Nanoparticles at Low Magnetic Fields
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Solution Overview
Problem
Current MRI technologies at ultra-low magnetic fields face challenges in obtaining high contrast images without compromising acquisition sensitivity, as conventional contrast agents are ineffective and require excessively long scan times, making them unsuitable for clinical use.
Innovation Solution
The use of biocompatible superparamagnetic nanoparticles, such as SPIONs, in combination with balanced steady-state free precession (bSSFP) pulse sequences for susceptibility-based imaging, which allows for rapid and sensitive imaging by adjusting parameters like RF tip angle and repetition time to achieve positive contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional contrast agents are used in ultra-low field MRI, then image contrast can be achieved, but scan times become excessively long making them unsuitable for clinical use
Solution Approach 1:
The patent changes the fundamental imaging parameter from T1/T2 relaxation-based contrast to susceptibility-based contrast. By using susceptibility-weighted imaging sequences optimized for ultra-low fields, the patent achieves high contrast images without requiring prolonged scan times, as susceptibility effects remain strong even at 6.5 mT while relaxation contrast becomes ineffective
Solution Approach 2:
The patent introduces superparamagnetic iron oxide nanoparticles (SPIONs) as intermediary contrast agents. These nanoparticles create local magnetic field inhomogeneities that enhance susceptibility contrast, allowing for bright imaging of anatomical structures and pathological processes at ultra-low fields without requiring long acquisition times
2Ease of manufacture
If ultra-low magnetic field strength is used to reduce cost and improve accessibility, then MRI becomes more accessible, but contrast between tissues is reduced
Solution Approach 1:
The patent changes the contrast mechanism parameter from relaxation-based (T1/T2) to susceptibility-based imaging. Susceptibility contrast is less dependent on magnetic field strength compared to relaxation contrast, allowing maintainment of tissue contrast differentiation even at ultra-low fields of 6.5 mT and below
Solution Approach 2:
The patent uses SPIONs as intermediary agents that create localized susceptibility differences. These nanoparticles generate strong local magnetic field perturbations that enhance tissue contrast independently of the main magnetic field strength, compensating for the reduced intrinsic contrast at ultra-low fields
3Measurement precision
If susceptibility imaging is attempted in ultra-low field MRI, then contrast can be generated, but the magnetization changes are over 100 times smaller than in conventional MRI
Solution Approach 1:
The patent introduces SPIONs as intermediary contrast agents that amplify susceptibility effects. These nanoparticles have high magnetic susceptibility and create strong local field inhomogeneities, compensating for the reduced overall magnetization at ultra-low fields and enabling detectable susceptibility contrast
Solution Approach 2:
The patent employs composite contrast agents combining superparamagnetic iron oxide cores with biocompatible coatings. This composite structure provides both high susceptibility for strong contrast and biocompatibility for clinical application, enabling susceptibility imaging at ultra-low fields despite reduced signal magnitude
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 high-sensitivity imaging of anatomical structures and diseases like cancer at ultra-low magnetic fields, reducing scan times significantly and providing clear diagnostic images, even at field strengths as low as 6.5 mT, making MRI more accessible and cost-effective for remote locations.
Implementation Method 1
Susceptibility imaging, an MRI technique commonly used at conventional field strengths, generates contrast via local magnetization differences in the substance being imaged. These magnetization differences are described by variations in susceptibility (the property of a material that indicates whether it is attracted into or repelled out of a magnetic field)
Implementation Method 2
These magnetization differences are described by variations in susceptibility (the property of a material that indicates whether it is attracted into or repelled out of a magnetic field) and are induced by the B0 magnetic field that the substance being imaged is placed in
Implementation Method 3
When placed in a uniform static magnetic field (B0), these nuclear spins will precess about the static field with a characteristic frequency known as the Larmor frequency
Implementation Method 4
As the spins precess at the Larmor frequency, so too does the net transverse magnetic moment, generating an oscillatory magnetic field that can be inductively detected to give a magnetic resonance signal
Implementation Method 5
If a substance containing these nuclear spins is subjected to a radiofrequency pulse (B1) at the Larmor frequency, the net alignment of the spins can be rotated relative to the static magnetic field, producing a net transverse magnetic moment
Implementation Method 6
These magnetic field gradients vary the magnetic field over the sample of interest, causing spatial variations in the Larmor frequency. Knowledge of the spatial shift in the Larmor frequency enables images of nuclear spin distribution to be reconstructed from sets of MR signals
Data Source
AI summary
Systems and methods are provided for susceptibility contrast imaging of nanoparticles at low magnetic fields. A susceptibility-based MRI technique, such as imaging with a balanced steady-state free precession (bSSFP) pulse sequence, may be used for imaging a contrast agent such as biocompatible superparamagnetic nanoparticles at ultra-low fields. The contrast agent and imaging technique may be used to improving the visibility of anatomical structures and detecting diseases, such as cancer, with low-field MRI.