Researchers at Michigan State University have developed a system that allows the imaging and identification of inflamed atherosclerotic plaques, which are considered to be at risk of rupture. Their system involves administering carbon nanotubes that are preferentially taken up by macrophages and monocytes, which tend to accumulate at inflamed plaques. The researchers then illuminate the blood vessel of interest with light and the carbon nanotubes vibrate, producing a sound in response. This photoacoustic effect allows the researchers to locate and visualize the plaques.
Atherosclerotic plaque rupture forms the basis for strokes and heart attacks, but at present, there is no technology available to definitively identify plaques that are at risk of rupture. “Currently, there is no effective way to accurately locate and treat vulnerable plaques before they lead to a heart attack or stroke,” said Eliver Ghosn, a researcher involved in the study. “We hope our studies will help change that.”
One tell-tale sign of a plaque at risk of rupture is that it is inflamed, and inflammation is exacerbated by and attracts a variety of white blood cells. It is these cells that this new technique seeks out. The approach involves administering carbon nanotubes that such cells tend to take up from their environment.
“The power of our new technique is in its selectivity,” said Bryan Smith, another researcher involved in the study. “There are certainly other methods to image plaques, but what distinguishes this strategy is that it’s cellular. We’re specifically looking at the cells – called macrophages and monocytes – that are most responsible for making a plaque vulnerable in the first place. If you look at a normal blood vessel versus one with a plaque, there’re a lot more macrophages and monocytes in the one with the plaque. And our method is really looking at the monocytes and macrophages. Virtually no other cell type takes up the nanoparticles.”
The researchers can then probe a blood vessel of interest using light to see if any plaques have significant levels of the carbon nanotubes in their vicinity. However, the tubes respond to light by emitting sound that can be detected using an ultrasound transducer.
“We shine light into an artery where we’ve delivered certain types of particles that can absorb that light,” said Smith. “As a product of the release of that energy, they can literally shout back at us in ways that we can detect and use to create 3D images.”
So far, the researchers have tested the particles in mice and were successfully able to identify inflamed plaques in their vasculature. Another option may be to load the particles with drugs that can help to treat the plaques.