Researchers Build MRI-Based Microscope

In this diagram, viruses (coloured orange) cling to the gold surface (yellow) at the end of a silicon cantilever. A magnetic tip (blue) creates a magnetic field that interacts with the viruses to create an image, using magnetic force resonance microscopy. Image: Martino Poggio, University of Basel

The use of MRI in scientific studies has been limited because it can’t image anything smaller than several cubic micrometers. Now scientists are combining the 3-D capability of MRI with the precision of a technique called atomic force microscopy. This combination enables 3-D visualisation of tiny specimens such as viruses, cells and potentially structures inside cells — a 100-million-fold improvement over MRI used in hospitals.

Last year, Christian Degen, MIT assistant professor of chemistry, and colleagues at the IBM Almaden Research Center used that strategy to build the first MRI device that can capture 3-D images of viruses. Last weekend, their paper reporting the ability to take an MRI image of a tobacco mosaic virus was awarded the 2009 Cozzarelli Prize by the National Academy of Sciences.

“It’s by far the most sensitive MRI imaging technique that has been demonstrated,” says Raffi Budakian, assistant professor of physics at the University of Illinois at Urbana-Champaign, who was not part of the research team.

Using nanoscale MRI to reveal the 3-D shapes of biological molecules offers a significant improvement over X-ray crystallography, which was key to discovering the double-helix structure of DNA but is not well suited to proteins because they are difficult to crystallize, says Budakian. “There’s really no other technique that can go in molecule by molecule and determine the structure,” he says. Figuring out such structures could help scientists learn more about diseases caused by malformed proteins and identify better drug targets.

Traditional MRI takes advantage of the very faint magnetic signals emitted by hydrogen nuclei in the sample being imaged. When a powerful magnetic field is applied to the tissue, the nuclei’s magnetic spins align, generating a signal strong enough for an antenna to detect. However, the magnetic spins are so weak that a very large number of atoms (usually more than a trillion) are needed to generate an image, and the best possible resolution is about three millionths of a meter (about half the diameter of a red blood cell).

More information on research is available from MIT.

Tags: Christian Degen, microscope, microscopy, MIT, MRI, University of Illinois at Urbana-Champaign