Rapid, High-Fidelity Medical Imaging Reveals Cancer, Arthritis in New Research
The all-optical PAT scanner reduces acquisition time from minutes to seconds and can visualize microvasculature changes to depths approaching 15 mm.
Dr Nam Huynh
Credit: UCL
Researchers from University College London (UCL) have developed a fast all-optical photoacoustic tomography (PAT) scanner hundreds of times faster than typical PAT scanners, which seems poised to greatly improve detection of diseases in multiple fields including cardiovascular medicine, oncology, dermatology and rheumatology.1
"We've come a long way with photoacoustic imaging in recent years, but there were still barriers to using it in the clinic. The breakthrough in this study is the acceleration in the time it takes to acquire images, which is between 100 and 1,000 times faster than previous scanners,” corresponding author, Professor Paul Beard, UCL Medical Physics and Biomedical Engineering and the Wellcome/EPSRC Centre for Interventional and Surgical Sciences, said in a statement.2
Early-generation PAT scanners are able to provide high resolution microvascular images but are not suitable for clinical use given their minutes-long acquisition times. To solve this problem, Beard and colleagues parallelized the optical architecture of the sensor readout by using excitation lasers with high pulse-repetition frequencies and exploited compressed sensing. This method successfully reduced scan times reduced to a few seconds and even hundreds of milliseconds, if modest reductions in image fidelity or lateral field of view are acceptable.1
"This speed avoids motion-induced blurring, providing highly-detailed images of a quality that no other scanner can provide. It also means that rather than taking 5 minutes or longer, images can be acquired in real time, making it possible to visualize dynamic physiological events,” Beard added.2 "These technical advances make the system suitable for clinical use for the first time, allowing us to look at aspects of human biology and disease that we haven't been able to before. Now more research is needed with a larger groups of patients to confirm our findings."
The fast, all-optical PAT scanner can volumetrically visualize individual arterioles, venules, venous valves and millimeter-scale arteries and veins to depths approaching 15 mm and can also provide dynamic 3D images of time-varying tissue perfusion and other hemodynamic events while minimizing motion-related artifacts.1
"Photoacoustic imaging could be used to detect the tumor and monitor it relatively easily. It could also be used to help cancer surgeons better distinguish tumor tissue from normal tissue by visualizing the blood vessels in the tumor, helping to ensure all of the tumor is removed during surgery and minimizing the risk of recurrence. I can envisage lots of ways it will be useful,” lead investigator Dr Nam Huynh, senior research fellow, UCL Medical Physics and Biomedical Engineering, added.2 Hyunh and Dr. Edward Zhang from UCL's Medical Physics and Biomedical Engineering served as co-lead investigators.
The investigators evaluated the new PAT scanner in healthy volunteers as well in people with suspected vascular changes associated with peripheral vascular disease, skin inflammation and rheumatoid arthritis (RA). In people at risk for peripheral vascular disease (PVD) and people with type 2 diabetes, they were able to detect evidence of vessel tortuosity and varying degrees of microvascular changes.1
"One of the complications often suffered by people with diabetes is low blood flow in the extremities, such as the feet and lower legs, due to damage to the tiny blood vessels in these areas. But until now we haven't been able to see exactly what is happening to cause this damage or characterize how it develops,” senior author Andrew Plumb, Associate Professor of Medical Imaging, UCL and consultant radiologist, UCL Hospital, added.2 "In one of our patients, we could see smooth, uniform vessels in the left foot and deformed, squiggly vessels in the same region of the right foot, indicative of problems that may lead to tissue damage in future. Photoacoustic imaging could give us much more detailed information to facilitate early diagnosis, as well as better understand disease progression more generally."
The scanner was also able to provide evidence of angiogenesis which could be helpful in diagnosing dermatological conditions as well as cancer and RA. First, investigators scanned regions of superficial skin inflammation around a raised papule on the forearm following a suspected insect bite and were able to visualize the angiogenesis. Then, in a patient with locally advanced breast cancer, the fast PAT imaging revealed an increase in contrast due to skin neovascularization, which could be seen by MRI but not by ultrasound examination or visual inspection. In patients with RA, the scanner was able to quickly reveal synovial thickening and increased blood flow in interphalangeal joints. Comparing RA joints with healthy joints, the scanner was able to show a significant difference in vascular contrast (P < 0.001).1
The investigators concluded that the fast, high-fidelity PAT scanner is practical and versatile and is ripe for clinical translation in a number of fields, including oncology, cardiovascular medicine, dermatology, and image guided surgery.
