Endoscopic Photoacoustic Imaging and Ultrasound Make for a Great Pair

Endoscopic Photoacoustic Imaging and Ultrasound Make for a Great Pair

Scientists from USC and Washington University in St. Louis have developed a new type of medical imaging that gives doctors a fresh look at live internal organs.

The technology combines two existing forms of medical imaging — photoacoustic and ultrasound — and uses them to generate a high-contrast, high-resolution combined image that could help doctors spot tumors more quickly.

“Photoacoustic endoscopy provides deeper penetration than optical endoscopy and more functional contrast than ultrasonic endoscopy,” said Lihong Wang, principal investigator and corresponding author of a study on the technology that appeared in Nature Medicine on July 15, and professor of biomedical engineering at Washington University.

Wang collaborated with Qifa Zhou, Ruimin Chen and Kirk Shung of USC, as well as Joon-Mo Yang, Christopher Favazza, Junjie Yao, Xin Cai and Konstantin Maslov from Washington University.

“This is the first time that we have had small endoscopy with two imaging modalities,” said Qifa Zhou, one of the principal investigators and corresponding authors of the study, and professor at the NIH Resource Center for Medical Ultrasonic Transducer Technology in the USC Department of Biomedical Engineering.

Currently, doctors routinely employ ultrasound endoscopy to study internal organs. This technique places an ultrasound camera, similar to ones used to create images of fetuses, on a flexible scope that can be inserted internally.

Though these images are typically high-resolution, they are also low-contrast — making a dim image, like a photograph shot in a poorly lit room.

To address the problem, Wang, Zhou and their teams added a photoacoustic-imaging device to the ultrasound endoscope. The resulting camera zaps organ tissue with a light. When the light is absorbed by tissue, the tissue gets slightly hotter and expands. That expansion produces a sound pressure wave that the ultrasound device on the endoscope picks up.

“This technology combines the best of both worlds,” said Shung, director of the NIH Resource Center and professor of biomedical engineering at USC.

The researchers have tested their new device inside the gastrointestinal tract, producing in vivo images detailed enough to show blood vessels, as well as the density of the tissue around them.

“This imaging has fine resolution and high contrast,” said Yang, a postdoctoral researcher in Wang’s group. With a clearer picture of what’s going on inside the gastrointestinal tract, doctors could potentially spot colon and prostate cancers earlier.

The research was funded by the National Cancer Institute at the National Institutes of Health.

At present, clinicians routinely apply ultrasound endoscopy in a variety of interventional procedures that provide treatment solutions for diseased organs. Ultrasound endoscopy not only produces high-resolution images, but also is safe for clinical use and broadly applicable. However, for soft tissue imaging, its mechanical wave–based image contrast fundamentally limits its ability to provide physiologically specific functional information. By contrast, photoacoustic endoscopy possesses a unique combination of functional optical contrast and high spatial resolution at clinically relevant depths, ideal for imaging soft tissues. With these attributes, photoacoustic endoscopy can overcome the current limitations of ultrasound endoscopy. Moreover, the benefits of photoacoustic imaging do not come at the expense of existing ultrasound functions; photoacoustic endoscopy systems are inherently compatible with ultrasound imaging, thereby enabling multimodality imaging with complementary contrast. Here we present simultaneous photoacoustic and ultrasonic dual-mode endoscopy and show its ability to image internal organs in vivo, thus illustrating its potential clinical application.

Researchers from Washington University in St. Louis and University of Southern California brought together two similar imaging modalities that turn out to work very well together in visualizing internal organs.

Photoacoustic imaging relies on a laser that excites soft tissue to vibrate and in turn produce a detectable audio signal which is characteristic of the tissue it’s coming from. Traditional ultrasound emits a regular high frequency audio wave and measures its characteristics when it bounces back. By combining the two into an endoscope and imaging at the same time, the team was able to capture individual organs at high resolution in a study on animals.

From the study abstract:

[P]hotoacoustic endoscopy possesses a unique combination of functional optical contrast and high spatial resolution at clinically relevant depths, ideal for imaging soft tissues. With these attributes, photoacoustic endoscopy can overcome the current limitations of ultrasound endoscopy. Moreover, the benefits of photoacoustic imaging do not come at the expense of existing ultrasound functions; photoacoustic endoscopy systems are inherently compatible with ultrasound imaging, thereby enabling multimodality imaging with complementary contrast. Here we present simultaneous photoacoustic and ultrasonic dual-mode endoscopy and show its ability to image internal organs in vivo, thus illustrating its potential clinical application.

Source : http://news.usc.edu/#!/article/39453/hybrid-medical-imaging-technology-may-shed-new-light-on-cancer/

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