Biomagnetics

Magnetic resonance imaging (MRI) gives detailed medical images of the body's internal tissues and organs without the use of harmful radiation. MRI is based on magnetic vibrations of the protons in water. The Biomagnetics Program seeks to improve MRI through the invention of multifunctional magnetic contrast agents and the development of measurements and standards to make MRI quantitative and traceable, instead of qualitative and instrument dependent. The Biomagnetics Program also develops terahertz detectors with unprecedented sensitivity and resolution for bioimaging, identification of trace chemical molecules, and remote atmospheric sensing to monitor climate change. The imaging of malignant skin tumors by the passive detection of terahertz radiation is safe and painless.

Customized microscopic magnets could add color and sensitivity to MRI. In collaboration with the NIH, EEEL has shown how such micromagnets could act as “smart tags” to identify particular cells, tissues, or physiological conditions. Each micromagnet consists of two round, vertically stacked magnetic disks, a few micrometers in diameter, separated by a gap. Customized magnetic fields can be created by adjusting materials, gap, or disk thickness or diameter. The open design allows the diffusion of water through the micromagnet, producing a signal that may be thousands of times stronger than that produced by a similarly sized, but stationary, volume of water. The diffusion effectively increases local MRI sensitivity, which could lead to faster imaging, images that are richer in information, or reduced dose requirements for contrast agents. The micromagnets can be made using conventional microfabrication techniques and are compatible with standard MRI hardware.

In collaboration with a committee of the International Society for Magnetic Resonance in Medicine (ISMRM), EEEL is developing a standard "phantom" for the calibration of MRI machines. Currently, MRI scanners drift over time and different machines give different images. Quantitative, traceable MRI will provide accurate and consistent images, validate disease mechanisms and therapeutic outcomes, and facilitate the transition to computer aided diagnostics. The pharmaceutical industry will use quantitative MRI to objectively test the efficacy of new drugs.

Biological and chemical samples naturally emit characteristic signatures of terahertz radiation, but detecting and measuring them is a challenge because the signals are weak and absorbed rapidly by the atmosphere. A prototype imager developed by EEEL uses a sensitive superconducting detector, microelectronics, and optics to operate in the terahertz range. The system can detect temperature differences smaller than one half degree Celsius, which could differentiate between, for example, tumors and healthy tissue. The technique is sensitive enough to detect the weak terahertz signals naturally emitted by samples, eliminating the need to actively illuminate them. The technology may become a new tool for early tumor detection and rapid and precise identification of chemical hazards for homeland security.

• Invented MRI contrast agents with spectral signatures based on the geometry of the magnetic microstructures.
• Developed and characterized a passive heterodyne hot electron bolometer imager operating at 850 gigahertz with spatial resolution of 4 millimeters.
• Showed that the efficiency of solutions of the single-molecule Fe-8 nanomagnet as an MRI contrast agent compared to that of gadolinium chelate depends on concentration.
• Developed a novel platform for microfluidic manipulation of magnetic particles based on an array of magnetic spin valves with bistable ferromagnetic “on” and antiferromagnetic “off” states.

Associated Publications/Reports:

• G. Zabow, S. Dodd, J. Moreland, A. Koretsky, “Micro-Engineered Local Field Control for High-Sensitivity Multispectral MRI,” Nature, vol. 453, pp. 1058-1063, June 2008.
• E. Gerecht, D. Z. Gu, L. X. You, K. S. Yngvesson, "A Passive Heterodyne, Hot Electron Bolometer Imager Operating at 850 GHz," IEEE Transactions on Microwave Theory and Techniques, vol. 56, pp. 1083-1091, May 2008.
• B. Cage, S. E. Russek, R. Shoemaker, A. J. Barker, C. Stoldt, V. Ramachandaran, N. S. Dalal, “The Utility of the Single-Molecule Magnet Fe-8 as a Magnetic Resonance Imaging Contrast Agent Over a Broad Range of Concentration,” Polyhedron, vol. 26, pp. 2413-2419, July 2007.