New handheld scanner generates 3D images in seconds to aid early diagnosis

A new handheld scanner developed by UCL researchers can generate highly detailed 3D photoacoustic images in just seconds, paving the way for their use in clinical settings for the first time and offering the possibility of earlier diagnosis of disease.

In the study, published in Natural biomedical engineering, the team shows that its technology can provide photoacoustic tomography (PAT) imaging scans to doctors in real time, providing them with precise and complex images of blood vessels, helping to inform patient care.

Photoacoustic tomography imaging uses laser-generated ultrasound waves to visualize subtle changes (an early marker of disease) in veins and arteries on a sub-millimeter scale up to 15 mm deep in human tissue.

However, until now, existing PAT technology has been too slow to produce 3D images of high enough quality for use by clinicians.

During a PAT scan, patients must be completely still, meaning any movement during a slower scan can cause images to be blurry and therefore does not guarantee clinically useful images.

Older PAT scanners took more than five minutes to take an image. By reducing this time to a few seconds or less, the image quality is much improved and much more suitable for people who are fragile or in poor health.

Researchers say the new scanner could help diagnose cancer, cardiovascular disease and arthritis within three to five years, subject to further testing.

Corresponding author Professor Paul Beard (UCL Medical Physics and Biomedical Engineering and Wellcome/EPSRC Center for Interventional and Surgical Sciences), said: “We have come a long way with photoacoustic imaging in recent years. , but there were still barriers to use. this at the clinic.

“The breakthrough of this study lies in the acceleration of the time required for image acquisition, which is between 100 and 1,000 times faster than that of previous scanners.

“This speed avoids motion-induced blur, providing highly detailed images with a quality that no other scanner can provide. This also means that instead of taking five minutes or more, images can be acquired in real time, allowing dynamic images to be viewed. physiological events.

“These technical advances make the system suitable for clinical use for the first time, allowing us to examine aspects of human biology and disease that we have not been able to examine before.

“Further research is now needed in larger numbers of patients to confirm our findings.”

Professor Beard added that a key potential use of the new scanner was to assess inflammatory arthritis, which requires scanning all 20 finger joints in both hands. With the new scanner, this can be done in minutes – old PAT scanners take almost an hour, which is too long for elderly and frail patients, he said.

Test the scanner on patients

In the study, the team tested the scanner in preclinical testing on 10 patients with type 2 diabetes, rheumatoid arthritis or breast cancer, as well as seven healthy volunteers.

In three patients with type 2 diabetes, the scanner was able to produce detailed 3D images of the microvasculature of the feet, highlighting deformations and structural changes in the vessels. The scanner was used to visualize skin inflammation related to breast cancer.

Andrew Plumb, Associate Professor of Medical Imaging at UCL and Consultant Radiologist at UCLH and lead author of the study, said: “One of the complications that people with diabetes often suffer from is low blood flow. in the extremities, such as the feet and lower parts. legs, due to damage to the tiny blood vessels in these areas. But until now, we have not been able to see exactly what happens to cause these lesions or characterize their evolution.

“In one of our patients, we were able to observe smooth, uniform vessels in the left foot and distorted, wavy vessels in the same region of the right foot, indicating problems that could lead to tissue damage in the future “Photoacoustic imaging could provide us with much more detailed information to facilitate early diagnosis, as well as to better understand disease progression more generally.”

Photoacoustic tomography

Since its initial development in 2000, PAT has long been considered to have the potential to revolutionize our understanding of biological processes and improve the clinical assessment of cancer and other major diseases.

It works by using the photoacoustic effect, which occurs when materials absorb light and produce sound waves.

PAT scanners work by firing very short laser bursts at biological tissue. Some of this energy is absorbed, depending on the color of the target, causing a slight increase in heat and pressure which in turn generates a weak ultrasound wave containing information about the tissue. The entire process takes place in just a fraction of a second.

In previous research, physicists and engineers at UCL (led by Professor Beard) discovered that the ultrasound wave can be detected using light.

In the early 2000s, they developed a system in which a sound wave causes tiny changes in the thickness of a thin plastic film that can be measured using a highly tuned laser beam.

The results revealed never before seen tissue structures.

How PAT could help with disease detection

For some conditions, such as peripheral vascular disease (PVD), a complication of diabetes, early signs of changes in tiny blood vessels indicative of the disease cannot be seen using conventional imaging techniques such as MRI.

But with PAT images it is possible, providing the possibility of treatment before tissue is damaged and avoiding poor wound healing and amputation, the journal says. PVD affects more than 25 million people in the United States and Europe, he adds.

Similarly, in cancer, tumors often have a high density of small blood vessels that are too small to be visible with other imaging techniques.

Dr Nam Huynh from UCL Medical Physics and Biomedical Engineering, who developed the scanner with his colleague Dr Edward Zhang, said: “Photoacoustic imaging could be used to detect the tumor and monitor it relatively easily.

“This could also be used to help cancer surgeons better distinguish tumor tissue from normal tissue by visualizing the tumor’s blood vessels, which would help ensure that the entire tumor is removed during surgery and minimize the risk of recurrence. I can envision many ways this will be helpful.”

Dr. Huynh added that one of the main advantages of this technology is that it is sensitive to hemoglobin. Ultrasound waves are produced by light-absorbing molecules like hemoglobin.

Improve and test scanner speed

In this study, UCL researchers sought to overcome the speed problem by reducing the time needed to acquire images. They achieved this by innovating the design of the scanner and the mathematics used to generate the images.

Unlike old PAT scanners, which measured ultrasound waves at more than 10,000 different points on the tissue surface, one by one, the new scanner detects them simultaneously at several points, thus significantly reducing image acquisition time.

The research team also used mathematical principles similar to those used in digital image compression. This made it possible to reconstruct high-quality images from a few thousand (instead of tens of thousands) of measurements of the ultrasound wave, thus speeding up image acquisition.

These innovations have reduced imaging time to seconds or less than a second, eliminating motion blur and allowing images of dynamic tissue changes to be taken.

The scientists said further research was needed with a wider group of patients to confirm their study results and to what extent the scanner would be clinically useful in practice.

The first steps to develop photoacoustic tomography for medical imaging were taken in 2000, but the origins of the technique date back to 1880, when former UCL student Alexander Graham Bell, just after inventing the telephone, observed the conversion of sunlight into audible sound.

In 2019, members of the UCL research team founded DeepColor Imaging, a UCL spin-out company which now markets a range of scanners based on PAT technology worldwide.