If heart attacks were the alarm bells, patients would have a better chance of avoiding them. This is the idea behind a new imaging technique developed by a team of researchers led by Spartan.
We project light into an artery where we have delivered certain types of particles capable of absorbing this light. As a product of the release of this energy, they can literally yell at us in a way that we can detect and use to create 3D images. “
Bryan Smith, Associate Professor, Michigan State University’s College of Engineering
To be clear, the sound signal is not audible to human ears, but it is easily picked up by an ultrasound transducer. Thanks to Smith and his colleagues, this technique can now be used to directly image atherosclerotic plaques, the medical term for fatty deposits that build up in the arteries and can lead to strokes and heart attacks.
The researchers presented the new technique in mice, the first step towards advancing the technology for use in humans. The team published their findings in an article now available online in the journal Advanced Functional Materials. The journal will also feature the work as a cover story in a September issue.
“The power of our new technique lies in its selectivity,” said Smith, who is the director of the Translational NanoImmunoEngineering Lab located at the Institute for Quantitative Health Science and Engineering, or IQ at MSU.
“There are certainly other methods of imaging plaques, but what sets this strategy apart is that it’s cellular,” Smith said. “We’re looking specifically at cells – called macrophages and monocytes -; which are most responsible for the vulnerability of a plaque in the first place. “
While it’s difficult to prove whether a particular plaque is responsible for a stroke or heart attack in a patient, the dominant idea is that vulnerable plaques are the most dangerous, Smith said. These are inflammatory plaques that can rupture and therefore block blood vessels.
In addition to fatty deposits, vulnerable plaques also contain many immune cells, including many macrophages and monocytes. Smith and his colleague developed nanoparticles -; tiny tubules made up of carbon atoms -; which naturally and specifically search for these cells.
By injecting the particles into mice, the researchers send the tubes to search for specific immune cells that collect in plaques. Researchers can then project laser light into the arteries. If there is plaque present, the particles will absorb light and emit sound waves. Researchers then use this acoustic signal to locate and visualize the plaque.
“If you look at a normal blood vessel compared to a vessel with a plaque, there are a lot more macrophages and monocytes in the one with the plaque,” Smith said. “And our method really examines monocytes and macrophages. Hardly any other type of cell takes up nanoparticles.”
The idea behind the coupling of light and sound, known as the photoacoustic effect, dates back to Alexander Graham Bell in the late 1800s, Smith said. Yet moving from this idea to medical diagnosis required the development of crucial technologies such as lasers and ultrasound. The technique is now maturing with the Food and Drug Administration approving a photoacoustic imaging machine to detect breast cancer earlier this year.
In the future, doctors will be able to image arterial plaques in a precise and non-invasive way thanks to the innovations of Smith and his team with nanoparticles. Researchers from Stanford and Emory Universities joined Smith on the project.
This exciting advancement in nanomedicine has only been possible thanks to our team of multidisciplinary experts. Currently, there is no effective way to accurately locate and treat vulnerable plaques before they lead to a heart attack or stroke. We hope our studies will help change that. “
Eliver Ghosn, project collaborator and assistant professor, Emory University School of Medicine and Lowance Center for Human Immunology
From a treatment standpoint, Smith’s lab has also already shown that he can package their nanoparticles with a drug used to fight plaques. In the future, the team will explore the use of these particles to aid in imaging and delivery of treatment.
“So you might ask, can you connect those ideas, develop a combination of therapy and diagnosis? I think the answer is absolutely yes,” Smith said. “There’s a lot of potential there. It’s in the pipeline.”