Magnetic microstructures for magnetic resonance imaging
Inventors
Zabow, Gary • Dodd, Stephen • Koretsky, Alan • Moreland, John
Assignees
United States Department of Commerce • US Department of Health and Human Services • Office of Technology Transfer
Publication Number
US-9084820-B2
Publication Date
2015-07-21
Expiration Date
2028-04-18
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Abstract
A magnetic resonance contrast agent has a medium, and a contrast structure dispersed in the medium. The contrast structure comprises a magnetic material arranged to create a local region of a local magnetic field such that nuclear magnetic moments of a material when arranged within the local region precess at a characteristic Larmor frequency about a total magnetic field in the local region while in use, the characteristic Larmor frequency being identifiable with the contrast structure, and the total magnetic field in the local region being a substantially spatially uniform magnetic field.
Core Innovation
The invention provides a magnetic resonance contrast agent comprising a medium and a contrast structure dispersed within that medium. The contrast structure is made of magnetic material arranged to create a local magnetic field region where nuclear magnetic moments of a material within this local region precess at a characteristic Larmor frequency. This frequency is identifiable with the contrast structure and the total magnetic field in this region is substantially spatially uniform.
The problem addressed is the limited capability of existing magnetic resonance imaging (MRI) contrast agents to produce multiplexed, spectrally distinct signals akin to optical imaging technologies. Traditional agents, such as superparamagnetic iron oxide nanoparticles or micrometer-sized iron oxide particles, generate continuous spatial decay fields that cause a broad range of Larmor frequencies, thereby broadening spectral lines and obscuring distinction between different magnetic particles. This limitation reduces the sensitivity and multiplexing potential of MRI, such as the ability to distinguish different cell types at the single-cell level.
The invention solves this by designing magnetic resonance structures that create homogeneous local magnetic fields within a near-field spatial region, enabling discrete, characteristic, and distinguishable Larmor frequency shifts. These structures might be microfabricated magnetic microstructures, such as pairs of spaced magnetic disks or hollow cylindrical shells, arranged so that the local magnetic field they create is spatially uniform and produces specific, identifiable spectral signatures. This engineering enables transformed MRI contrast agents from simple binary markers into “colored” spectrally distinguishable tags, thereby enhancing MRI sensitivity and multiplexing capability far beyond conventional chemically synthesized agents.
Claims Coverage
The patent includes two independent claims related to a magnetic resonance contrast agent and a magnetic resonance identity system. The claims focus on the structural configuration and functional magnetic properties of the contrast agent.
Magnetic contrast structure with spaced disk-shaped magnetic components
A contrast structure comprising a pair of solid disk-shaped magnetic components arranged with their circular surfaces parallel and centers aligned along a common axis normal to the surfaces, defining a fixed space between them that creates a spatially extended near-field region with a homogeneous magnetic field. This region causes nuclear magnetic moments within it to precess at a characteristic Larmor frequency identifiable with the contrast structure, enabling characteristic magnetic resonance signals.
Magnetic resonance contrast agent adapted for frequency-shifted nuclear magnetic resonance
The contrast agent provides a frequency-shifted nuclear magnetic resonance signal by employing a contrast structure whose magnetic material arrangement and space between disk components yield a substantially uniform local magnetic field in the near-field region, allowing nuclear magnetic moments to precess at a distinct Larmor frequency usable in MRI or NMR systems.
Magnetic resonance identity system incorporating the contrast agent
A system comprising the described magnetic resonance contrast agent, a source of electromagnetic radiation to illuminate the contrast agent with excitation radiation, and a detection system to detect the characteristic magnetic resonance signals emitted from the contrast agent, enabling identification based on the specific spectral signatures of the contrast structure.
The claims collectively cover a magnetic resonance contrast agent featuring a specific geometric arrangement of magnetic materials to create uniform local magnetic fields producing discrete Larmor frequency shifts, and systems leveraging such agents for spectral identification in MRI or NMR applications.
Stated Advantages
The invention enables frequency-shifted, spectrally distinct MRI contrast agents that elevate MRI sensitivity and multiplexing beyond traditional chemically synthesized agents.
Microfabrication allows engineered structural properties and increased functionality, including lower concentration requirements and enhanced signal-to-noise ratios.
The structures can self-align with external magnetic fields ensuring proper orientation for meaningful spectral signals.
Open structures permit fluid diffusion, enhancing signal amplification through magnetization transfer effects and enabling detection of individually distinguishable micro-tags.
Spectral shifting is independent of background magnetic field strength, allowing tunable frequency shifts determined by geometric parameters of the magnetic microstructures.
The agents can serve as local physiological probes and may be designed for 'smart' sensing by modulating spectral signals in response to environmental changes such as pH or enzymatic activity.
The invention supports non-invasive flow tagging and potentially allows monitoring of fluid flow in medical and industrial contexts.
Documented Applications
MRI contrast agents for enhanced multiplexed imaging with spectrally distinct tags.
Magnetic resonance identity systems enabling detection and differentiation of micro-tagged objects or cells.
Tracking and distinguishing of different cell types at the single-cell level in biological research and diagnostics.
MRI fluid flow and blood perfusion labeling by spin-tagging fluid passing through magnetically structured regions.
Calibration and spatial markers for MRI/NMR systems using sets of microstructures with known frequency shifts.
Magnetic field sensors and physical parameter sensors including pressure, vibration, torque, and orientational measurements based on changes in microstructure properties.
Magnetic separation techniques analogous to magnetic bead protocols.
Micro-RFID tags and RFID-enabled microfluidics using magnetic resonance based spectral identification.
Localized RF magnetic heating elements for targeted thermal ablation of specific cells.
Measurement and imaging of fluid flow in microfluidic channels, industrial pipelines, and stents using arrays of magnetic resonance structures.
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