New imaging technique could make tissues practically transparent

Researchers at the University of California Berkeley have used a new imaging technology known as magnetic particle imaging (MPI) to image past tissue and organs to detect diseases deep inside the body.

While the research is still a few years from clinical use, the MPI technology has already shown high-quality scans in animal research.

Fibrous tissues can make it difficult to detect breast tumors in mammograms. Other imaging technologies like X-rays and PET scans can expose patients to harmful radiation.

The UC Berkeley system uses small quantities of magnetic iron oxide nanoparticles as tracers, which are as small as two billionths of a gram or less than a thousandth the width of a human hair. The tracers are small enough that they can be safely injected into a vein.

With precise delivery, the nanoparticles are able to target a disease and the tracers show up bright against a dark background, making the tissues in the way practically invisible.

“It’s like looking for starts at night instead of during the day,” Steven Conolly, a researcher on the project, said in a press release. “MPI can see the magnetic tracers with superb contrast and the physician can ‘see’ disease through the healthy background tissue.”

The researchers say that getting the nanoparticles to target a specific disease is one of the main challenges of advancing MPI. The team is currently developing techniques that allow the nanoparticles to gather in tumors and other diseases with high specificity and resolution.

MPI works similarly to MRI, but magnetic nanoparticles set the two imaging techniques apart. When the nanoparticles are exposed to two magnetic fields, the particles flip north to south and back again as water molecules do in MRI imaging. The energy is released and can be converted into voltage waveforms that are reconstructed into a 3D image on the computer.

One of the key differences is an MRO forms a picture of water in the body, even in muscles and tissue. MPI only creates images of the magnetic tracers.

If an MPI scan detects possible diseased tissue, the images can be overlaid on X-ray, CT or MRI anatomic images to show where the disease may be in relation to the anatomy of the patient.

So far, the researchers have tested the imaging technique in animal studies and have been shown to quickly pick up nanoparticles that have been injected into a vein in order to detect life-threatening gastrointestinal bleeds.

The researchers also found that the 3D MPI images are able to provide the lung images needed to diagnose pulmonary embolism without the need for radiation. It can also visualize cerebral blood volume in small capillaries, which could provide a noninvasive diagnosis for stroke.

Conolly and his research team now plan to improve the scanner hardware and enhance the magnetic nanoparticles to reach single-cell sensitivity for preclinical research studies.

“Our next challenge is to improve the nanoparticles for high-resolution images,” Conolly said. “That would translate into smaller, affordable scanners for diagnosing tumors and other diseases in patients. I’m confident that research in our field will soon allow MPI to provide life-saving diagnoses and treatments.”