MRI contrast using solid-state, B1-distorting, microelectromechanical systems (MEMS) microresonant devices (MRDs)

Area of Science:

• Biomedical Engineering
• Magnetic Resonance Imaging
• Materials Science

Background:

• Current MRI signal and contrast rely on proton concentration and relaxivity.
• Nonchemical, solid-state devices offer a novel approach to MRI signal generation and contrast enhancement.
• Microelectromechanical systems (MEMS) technology enables fabrication of micro-scale devices.

Purpose of the Study:

• To introduce and evaluate microresonant devices (MRDs) as a new method for generating MRI signals and contrast.
• To demonstrate the feasibility of using solid-state MRDs for in vitro and in vivo MRI applications.
• To lay the groundwork for developing a new class of non-radioactive, solid-state MRI contrast agents.

Main Methods:

• Fabrication of 15-micrometer-thick, coil MRDs using MEMS technology with tantalum oxide capacitors and copper inductors.
• Design of MRDs to resonate at the proton Larmor frequency (127.7 MHz) at 3T.
• Characterization of MRD performance (B(1) field, Q factor) in saline using RF scanning microscopy and a clinical 3T MRI scanner.
• In vivo testing of subcutaneously implanted MRDs in mice.

Main Results:

• MRDs with diameters from 300 to 1000 microm were successfully fabricated and characterized.
• Measured B(1) fields ranged from 3.25 to 3.98 microT, with quality factors (Q) between 3.9 and 7.2.
• In vivo experiments confirmed that only MRDs tuned to the proton resonant frequency produced a measurable B(1) field when implanted in mice.

Conclusions:

• Microresonant devices (MRDs) represent a novel solid-state approach for generating detectable MRI signals and contrast.
• The study demonstrates proof-of-principle for MRD functionality in vitro and in vivo.
• MRDs hold potential as a new category of MRI contrast agents, offering an alternative to traditional chemical agents.