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Oct 15, 2010 (Vol. 30, No. 18)

In Vivo Imaging Transfigured by MRI

Researchers Have Their Sights Set on Emerging Tools for Faster and Improved Operations

  • Magnetic Particles

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    Philips Research has developed a new medical imaging technology called magnetic particle imaging (MPI). The technology is based on the magnetic properties of injected iron-oxide nano particles.

    “Pure anatomical imaging is changing to quantitative and functional imaging,” according to Jörn Borgert, Ph.D., senior scientist, Philips Research. Last year in preclinical studies, Dr. Borgert says, Philips became the first to show that magnetic particle imaging (MPI) could produce real-time in vivo images that accurately capture cardiovascular activity.

    MPI is becoming especially valuable in diagnosing unknown conditions. It could provide one very focused exam that provides the information more often gained by a battery of tests, such as ultrasounds and cardiac catheterization, without background noise.

    “Cardiovascular imaging is not the only field where this can have applications,” says Dr. Borgert, who was not one of the participants in the Gordon Research conference. MPI also may be used in oncology to follow the microvascularization of tumors, and other studies that require extreme sensitivity for cellular imaging, labeling, and tracking.

    MPI uses the same magnetic iron oxide material as a contrast material that is used for MRI. The iron-oxide nanoparticles are injected into the bloodstream, Dr. Borgert says. “The method involves direct measurement of the magnetization of the particles.” The result is a 3-D image of the iron oxide that can be 1,000 times more sensitive than MRI, he explains, so operators have the choice of high spatial and temporal resolution or of using less material.

    Image acquisition times may be as short as one-fiftieth of a second. That lets researchers look, for example, at the beating heart of a mouse and identify functional changes, Dr. Borgert points out. With a frame rate of 46 volumes per second, smooth video sequences can be generated. The first studies generated a resolution of approximately 1.5 mm along one axis and 3 mm along the other two axes, but the researchers are convinced that with optimized image-acquisition procedures, submillimeter resolution is possible.

    A prototype version in preclinical demonstrations for small rodents currently provides 3-D images using a 3 cm imaging bore. A larger 12 cm radius bore is also at the prototype stage, and a 40–60 cm bore version is being developed for human applications. “We need to acquire more knowledge about its clinical value,” Dr. Borgert emphasizes. “We’re approaching those tests step by step.”

    “It’s very difficult, technically, to scale-up,” he adds. The key challenge, at this point, centers around magnetic field strength.

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