Novel Approach Improves Photoacoustic Imaging

Photoacoustic imaging has the potential to transform diagnostic imaging as it can capture  images without causing pain or using ionizing radiation. However, its use has been limited by the absence of intrinsic chromophores. Now, researchers in South Korea have proposed a new contrast agent for photoacoustic imaging that they say provides deeper imaging depth and is feasible for preclinical studies and warrants additional investigation for clinical use.

The principle of photoacoustic imaging is that it allows lights to be absorbed by tissues, which then causes a thermoelastic expansion of the tissues of the organs instantly. This generates sound wave (photoacoustic) signals that are detected as ultrasound wave sensors, producing images. Conventional optical microscopic imaging technologies only allow observing tissues in 1 mm depth. Photoacoustic imaging system produces images of the deep tissues in animals and humans based on optical contrast.

However, an issue with photoacoustic imaging is that it is difficult to observe deep tissues in various organs. Specifically, it is hard to cost-effectively deliver enough light at 650~900nm short-wavelength to deep tissues in the body. For this reason, the commercial and clinical translation of photoacoustic imaging have been challenging.

To improve on this limitation, the research team introduced a nanoparticle nickel-based contrast agent that absorbs light specifically and strongly at 1,064 nm to observe deep tissues. They verified biocompatibility of nickel-based nanoparticles and obtained photoacoustic images in deep tissues (3.4cm depth) of lymph nodes, gastrointestinal tracts, and the bladders of live rats.

According to Byullee Park, first author of a paper published recently in Theranostics, "This research is different from the previous studies that used short wavelength. We used long wavelength lasers and were able to minimize damages in the tissues. We were also able to obtain images of deep tissues by delivering lights to organs located in deep inside of the animal."

“When this newly developed photoacoustic imaging technique is applied to clinical practices, it can help diagnosis of diseases related to deep organs by producing images noninvasively and without a risk of explosion to radiation unlike other imaging methods that need radiations such as computed tomography (CT). Furthermore, lasers of 1,064 nm are comparatively economical, and can be used with other commercial ultrasound machines, which bring anticipation of its early clinical applications.”