New Scanner Creates 3D Images of Blood Vessels in Seconds

A new scanner can provide three-dimensional (3D) photoacoustic images of millimeter-scale veins and arteries in seconds.

The scanner, developed by researchers at University College London (UCL), London, England, could help clinicians better visualize and track microvascular changes for a wide range of diseases, including cancer, rheumatoid arthritis (RA), and peripheral vascular disease (PVD).

On left, a photoacoustic tomography (PAT) image of inflammation in the synovial region of an affected proximal interphalangeal joint on the ring finger of a patient with RA shows increased vascular contrast, indicated by the white ellipsis on bottom image. On right, an unaffected proximal interphalangeal joint on the patient’s index finger.

In exploratory case studies, researchers demonstrated how the scanner visualized vessels with a corkscrew-like structure in patients with suspected PVD and mapped new blood vessel formation driven by inflammation in patients with RA.

The case studies “illustrate potential areas of application that warrant future, more comprehensive clinical studies,” the authors wrote. “Moreover, they demonstrate the feasibility of using the scanner on a real-world patient cohort where imaging is more challenging due to frailty, comorbidity, or pain that may limit their ability to tolerate prolonged scan times.”

The work was published online in Nature Biomedical Engineering on September 30, 2024.

Improving Photoacoustic Imaging

PAT works using the photoacoustic effect, a phenomenon where sound waves are generated when light is absorbed by a material. When pulsed light from a laser is directed at tissue, some of that light is absorbed and causes an increase in heat in the targeted area. This localized heat also increases pressure, which generates ultrasound waves that can be detected by specialized sensors.

While previous PAT scanners translated these soundwaves to electric signals directly to generate imaging, UCL engineers developed a sensor in the early 2000s that can detect these ultrasound waves using light. The result was much clearer, 3D images.

“That was great, but the problem was it was very slow, and it would take 5 minutes to get an image,” explained Paul Beard, PhD, professor of biomedical photoacoustics at UCL and senior author of the study. “That’s fine if you’re imaging a dead mouse or an anesthetized mouse, but not so useful for human imaging,” he continued, where motion would blur the image.

In this new paper, Beard and colleagues outlined how they cut scanning times to an order of seconds (or fraction of a second) rather than minutes. While previous iterations could detect only acoustic waves from one point at a time, this new scanner can detect waves from multiple points simultaneously. The scanner can visualize veins and arteries up to 15 mm deep in human tissue and can also provide dynamic, 3D images of “time-varying tissue perfusion and other hemodynamic events,” the authors wrote.

With these types of scanners, there is always a trade-off between imaging quality and imaging speed, explained Srivalleesha Mallidi, PhD, an assistant professor of biomedical engineering at Tufts University in Medford, Massachusetts. She was not involved with the work.

“With the resolution that [the authors] are providing and the depth at which they are seeing the signals, it is one of the fastest systems,” she said.

Clinical Utility

Beard and colleagues also tested the scanner to visualize blood vessels in participants with RA, suspected PVD, and skin inflammation. The scanning images “illustrated how vascular abnormalities such as increased vessel tortuosity, which has previously been linked to PVD, and the neovascularization associated with inflammation can be visualized and quantified,” the authors wrote.

On left, a PAT image showing maximal inflammation (dashed white ellipsis) following a suspected insect bite is seen under a raised skin papule on the forearm, and on right, the inflammation is fully subsided under the site of the papule 38 days later. 

The next step, Beard noted, is testing whether these characteristics can be used as a marker for the progression of disease.

Nehal Mehta, MD, a cardiologist and professor of medicine at the George Washington University in Washington, DC, agreed that more longitudinal research is needed to understand how the abnormalities captured in these images can inform detection and diagnosis of various diseases.

“You don’t know whether these images look bad because of reverse causation — the disease is doing this — or true causation — that this is actually detecting the root cause of the disease,” he explained. “Until we have a bank of normal and abnormal scans, we don’t know what any of these things mean.”

Though still some time away from entering the clinic, Mehta likened the technology to the introduction of optical coherence tomography in the 1980s. Before being adapted for clinical use, researchers first needed to visualize differences between normal coronary vasculature and myocardial infarction.

On left, a PAT image of the foot of a patient with severe type 2 diabetes and suspected peripheral vascular disease shows a disorganized, irregular microvascular architecture with several tortuous vessels, some exhibiting a corkscrew structure. On right, the healthy foot vasculature of a person without PVD.

“I think this is an amazingly strong first proof of concept,” Mehta said. “This technology is showing a true promise in the field imaging.”

The work was funded by grants from Cancer Research UK, the Engineering & Physical Sciences Research Council, Wellcome Trust, the European Research Council, and the National Institute for Health and Care Research University College London Hospitals Biomedical Research Centre. Beard and two coauthors are shareholders of DeepColor Imaging SAS to which the intellectual property associated with the new scanner has been licensed, but the company was not involved in any of this research. Mallidi and Mehta had no relevant disclosures.