Photoacoustic Technique Captures Real-Time Anomalies in Microvasculature

DOUGLAS FARMER, SENIOR EDITOR
doug.farmer@photonics.com

By using a laser to generate ultrasound waves that reveal structural changes, photoacoustic tomography (PAT) has shown its value in identifying disease conditions in the microvasculature, the tiny vessels that extend from major veins and arteries. To this point, however, the process has been too slow to capture this information in real time, limiting its value in clinical settings. That is now changing, thanks to a device developed at University College London (UCL) that doctors could potentially hold right in their hands.

Traditionally, PAT scans have required a patient to remain motionless for an extended period of time to prevent blurring, but the UCL scanner enables such images in seconds by measuring ultrasound waves at numerous points simultaneously.

An image of the upper surface of a subject’s tongue, generated with photoacoustic tomography. Courtesy of Paul Beard/University College London.

“Some previous PAT scanners that use piezoelectric detectors arrays were fast but image quality was limited due to the non-ideal acoustic characteristics of piezoelectric detectors,” said Paul Beard, a professor in the UCL Department of Medical Physics and Biomedical Engineering. “We developed our optical sensor-based system some years ago which gave better image quality but it was slow (5 mins for a 3D image) precluding clinical use.”

The scanner was built for the current study with components including an optical parametric oscillator excitation laser pulses — delivered through optical fiber, which generated the ultrasound waves — and a Fabry-Perot ultrasound scanner to generate a map of the effects they revealed. The speed to acquire images is reduced by using high pulse repetition frequency lasers, parallelizing the readout and compressed sensing, said Beard.

In their study, the group used the scanner during preclinical examination on 10 patients with type-2 diabetes, rheumatoid arthritis, and breast cancer, along with seven healthy volunteers. In those with diabetes, deformation in the blood vessels in the feet were clearly identified. They also captured the inflammation present during breast cancer. They obtained detailed images from the fingertip and wrist, and demonstrated its utility for the tongue as well (see accompanying image).

“We demonstrated dynamic capability in the fingertip and wrist, but in principle this could be done on any part of the body,” Beard said.

Researchers noted that the PAT scanner has significant implications for patients suffering from peripheral vascular disease, in which blood vessels narrow or become blocked, especially in the hands or feet. Causes range from smoking to elevated cholesterol. Ultrasound is often used in diagnosis but it has difficulty capturing the flow present or lacking in smaller blood vessels.

Beard said the next step will be to draw from a larger study cohort. “The group will be drawn from hospital patients with arthritis and peripheral vascular disease in the near future,” he said. “We also plan to evaluate the device as a tool for guiding cancer and plastic surgery.”

The UCL team’s research was supported by Cancer Research UK, the Engineering & Physical Sciences Research Council, Wellcome, the European Research Council, and the National Institute for Health Research University College London Hospitals Biomedical Research Centre.

The research was published in Nature Biomedical Engineering (www.doi.org/10.1038/s41551-024-01247-x).