Could light and sound rid heart imaging of scary radiation?

Light and sound may one day replace current medical imaging techniques that require potentially harmful radiation, according to a new study.

Researchers demonstrated the method in a heart procedure but say they could potentially apply it 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.

“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,” says senior author Muyinatu Bell, assistant professor of electrical and computer engineering at Johns Hopkins University, director of the Photoacoustic & Ultrasonic Systems Engineering (PULSE) Lab. “The results are highly promising for future iterations of this technology.”

Bell and colleagues tested the technology during a cardiac intervention, a procedure in which a long, thin tube called a 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.

Doctors currently most commonly use a technique called fluoroscopy, a sort of x-ray movie, that can only show the shadow of where the catheter tip is and doesn’t provide detailed information about depth.

Additionally, this current visualization technology requires ionizing radiation, which can be harmful to both the patient and the doctor, Bell says.

Photoacoustic imaging, simply explained, is the use of 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. An ultrasound probe can the receive the sound wave and reconstruct it 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 they could use photoacoustic imaging to reduce radiation exposure by testing a new robotic system to automatically track the photoacoustic signal.

For this study, researchers 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.

They then performed cardiac catherization on two pigs under anesthesia and used fluoroscopy to initially map the catheter’s path on its way to the heart.

Bell’s team also successfully used robotic technology to hold the ultrasound probe and maintain constant visualization 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 team needs to perform more experiments to determine whether they can miniaturize the robotic photoacoustic imaging system and use it to navigate more complicated pathways, as well as perform clinical trials to definitively prove safety, they say the findings are a promising step forward.

“We envision that ultimately, this technology will be a complete system that serves the four-fold purpose of guiding cardiologists towards 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.

The paper will appear in IEEE Transactions in Medical Imaging.

Source: Johns Hopkins University

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