Magnetic resonance imaging (MRI) has become an invaluable, widely used medical diagnostic and research tool, but despite numerous chemically synthesized image-enhancing agents, MRI still lacks the sensitivity and the multiplexing capabilities of optical imaging that benefit from colored fluorophores — multi-spectral quantum dots for multi-functional encoding and biomolecular/cellular labeling.
Being able to distinguish with MRI between different types of cells at the single-cell level would profoundly impact cellular biology and early disease detection and diagnosis. Currently, MRI cell tracking employs the magnetically dephased signal from the water surrounding cells labeled with many superparamagnetic iron oxide nanoparticles (SPIOs) or dendrimers, or individual micrometer-sized iron oxide particles (MPIOs) that benefit from increased robustness and immunity to label dilution via cell division. However, the continuous spatial decay of the external fields surrounding these, or any other, magnetizable particles imposes a continuous range of Larmor frequencies that broadens the water line, obscuring distinction between possible different types of magnetic particles that might specifically label different types of cells. Their utility would be greatly enhanced if they could instead frequency-shift the water by discrete controllable amounts, transforming a monochrome/binary contrasting agent (magnetically labeled or not) into a “colored” spectral set of distinguishable tags. There is thus a need for improved MRI contrast agents.
Microfabricated structures can be used as MRI contrast agents with enhanced functionality or as micro-RFID (radio-frequency identification) tags. The microstructures can be engineered to appear as different effective colors when resolved using MRI, as opposed to strictly greyscale contrast of existing MRI agents. In this way, they can be thought of as radio-frequency analogs to quantum dots. A set of agents could be produced that would enable in-vivo labeling and tracking of multiple different types of cells simultaneously. The agents can also act as radio-frequency probes of various physiological conditions.
The 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. Nuclear magnetic moments of a material when arranged within the local region process at a characteristic Larmor frequency about a total magnetic field in the local region while in use. The characteristic Larmor frequency is identifiable with the contrast structure, and the total magnetic field in the local region is a substantially spatially uniform magnetic field.
A method of producing a magnetic resonance contrast agent includes forming contrast structures on a substrate, separating them from the substrate, and dispersing the contrast structures in a medium.