An imaging technique that uses light and sound could someday replace current methods that require potentially harmful radiation, according to the results of a new study led by Muyinatu Bell, assistant professor of electrical and computer engineering.
The findings detail success in a heart procedure but can potentially be applied to any procedure that uses a catheter, such as in vitro fertilization, or surgeries using the da Vinci robot, where clinicians need a clearer view of large vessels. The research was published in IEEE Transactions on Medical Imaging.
“This is the first time anyone has shown that photoacoustic imaging can be performed in a live animal heart with anatomy and size similar to that of humans. The results are highly promising for future iterations of this technology,” says Bell, director of the Photoacoustic & Ultrasonic Systems Engineering Lab.
Bell’s team of PULSE Lab members and cardiologist collaborators tested the technology during a cardiac intervention in which a long, thin catheter is inserted into a vein or artery, then threaded up to the heart to diagnose and treat various heart diseases, such as abnormal heartbeats.
Currently, providers most commonly use a technique called fluoroscopy, a sort of X-ray movie that requires ionizing radiation, which can be harmful to both the patient and the provider. This technique can only show the shadow of where the catheter tip is and doesn’t provide detailed information about depth.
Photoacoustic imaging uses light and sound to produce images. When energy from a pulsed laser lights up an area in the body, that light is absorbed by photoabsorbers within the tissue, such as the protein that carries oxygen in blood (hemoglobin), which results in a small temperature rise. This increase in temperature creates rapid heat expansion, which generates a sound wave. The sound wave can then be received by an ultrasound probe and reconstructed into an image.
Past studies of photoacoustic imaging mostly looked at its use outside of the body, such as for dermatology procedures, and few have tried using such imaging with a laser light placed internally. Bell’s team wanted to explore how photoacoustic imaging could be used to reduce radiation exposure by testing a new robotic system to automatically track the photoacoustic signal.
For this study, Bell’s team first placed an optical fiber inside a catheter’s hollow core, with one end of the fiber connected to a laser to transmit light; this way, the optical fiber’s visualization coincided with the visualization of the catheter tip.
Bell’s team then performed cardiac catheterization on two pigs under anesthesia and used fluoroscopy initially to map the catheter’s path on its way to the heart. The researchers also successfully used robotic technology to hold the ultrasound probe and maintain constant visualization of the photoacoustic signal, receiving image feedback every few millimeters.
Finally, the team looked at the pig’s cardiac tissue after the procedures and found no laser-related damage. While the researchers need to perform more experiments to determine whether the robotic photoacoustic imaging system can be miniaturized and used to navigate more complicated pathways, as well as perform clinical trials to definitively prove safety, they say these findings are a promising step forward.
“We envision that ultimately, this technology will be a complete system that serves the fourfold purpose of guiding cardiologists toward the heart, determining their precise locations within the body, confirming contact of catheter tips with heart tissue, and concluding whether damaged hearts have been repaired during cardiac radiofrequency ablation procedures,” says Bell.