Field Cycling Method for Hyperpolarized MRI Signal Preservation
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Solution Overview
Problem
NMR techniques face low sensitivity and significant magnetization loss due to relaxation when hyperpolarized nuclei are transported and used in vivo, particularly in MRI and MRS experiments, as the delay between preparation and measurement allows for magnetization decay.
Innovation Solution
A method involving non-hydrogenating para-hydrogen induced polarization (NH-PHIP) to generate hyperpolarized substrate molecules in a singlet or pseudo singlet state at a low magnetic field, followed by rapid field switching to a higher magnetic field within the MRI magnet to convert these states into observable magnetization, minimizing relaxation losses during the experiment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hyperpolarized sample is prepared outside the magnet and transported to the magnet for NMR experiment, then the sample can be hyperpolarized using dissolution DNP or NH-PHIP techniques, but magnetization is lost through relaxation during the transport delay
Solution Approach 1:
The sample is hyperpolarized in advance outside the magnet using dissolution DNP or NH-PHIP techniques, but the key innovation is that the hyperpolarized sample is then injected into the magnet while it is in a low-field state (below 100 mT), preserving the magnetization during what would normally be a lossy transport period
Solution Approach 2:
The magnet's field strength is dynamically changed: first kept low (below 100 mT) during sample injection to preserve magnetization, then rapidly switched to high field (above 200 mT) for the NMR measurement to achieve high signal intensity. This parameter switching resolves the contradiction between preserving magnetization and achieving high signal
2Duration of action of moving object
If time is allowed for hyperpolarized nuclei to migrate to the area of interest via blood stream and for metabolic processes to evolve, then in vivo NMR imaging can be performed, but relaxation losses become particularly severe
Solution Approach 1:
The magnetic field strength is switched from low (below 100 mT) during injection to high (above 200 mT) for measurement, enabling both extended observation time for metabolic processes and high signal intensity for detection, thereby resolving the contradiction between duration and magnetization loss
3Measurement precision
If the magnet is switched on to high field strength immediately after sample injection, then high signal intensity can be achieved for NMR measurement, but the singlet or pseudo singlet state has not had time to convert into observable magnetization
Solution Approach 1:
The magnet is prepared in the low-field state before sample injection, allowing the hyperpolarized sample to be introduced while preserving its singlet state. The field is then switched to high strength to enable conversion to observable magnetization and subsequent measurement
Solution Approach 2:
The magnetic field strength is switched from low (below 100 mT) during injection to high (above 200 mT) for measurement, enabling both extended observation time for metabolic processes and high signal intensity for detection, thereby resolving the contradiction between duration and magnetization loss
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 significantly reduces magnetization loss by maintaining hyperpolarized states during transport and metabolic processes, allowing for high-quality MRI or MRS measurements with extended observation times and improved sensitivity.
Implementation Method 1
polarizing the substrate molecules by non-hydrogenating para-hydrogen induced polarization (=NH-PHIP) into a singlet state or pseudo singlet state
Implementation Method 2
switching the magnet on to a static magnetic field strength inside the magnet higher than 200 mT, in particular higher than 500 mT, such that in at least a part of the substrate molecules and/or their metabolites in the singlet or pseudo singlet state, the singlet or the pseudo singlet state is converted into observable magnetisation
Data Source
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AI summary
An NMR experiment on hyperpolarizable magnetic nuclei of substrate molecules in a living human or animal body, with: a) the substrate molecules are polarized by non-hydrogenating para-hydrogen induced polarization (=NH-PHIP) into a singlet/pseudo singlet state in low magnetic field ; b) the substrate molecules are injected into the living body, wherein said body or a part thereof is already located inside a magnet at low magnetic field; c) the magnet is switched on to high magnetic field, and in at least part of the substrate molecules, the singlet state/pseudo singlet state is converted into observable magnetisation; d) an MRI or MRS measurement is carried out with the living body or the part thereof, collecting data from the substrate molecules. The NMR experiment is well applicable on hyperpolarized nuclei within a patient, with reduced losses of magnetization due to relaxation processes.