Biomedical engineers can now take a live look at the inner workings of a live small animal with high resolution using lasers.
This new technique is called “single-impulses photoacoustic computed tomography” (SIP-PACT). SIP-PACT uses light and ultrasounds to see the inner workings of a live animal. Researchers from Duke University and CalTech have developed hybrid imaging technology that breaks current resolution levels and speed barriers currently in use for small-animal whole-body imaging. It provides a full view of a small animal’s internal organs in real time. This imaging was previously only available in small areas of the body.
Traditional light-based imaging provides fast, high-resolution imaging that retains important functional information based on the wavelengths of light that the tissue absorbs reflects or emits. But this imagining is limited to just a few millimeters. Ultrasound waves can travel easily through tissue and provide an in-depth view, but they can’t read the tissue’s chemical components. Magnetic resonance imaging (MRI) can see deep into tissue, but it requires strong magnetic field and can take a long time to form the image. X-rays and positron emission tomography (PET) deliver too much radiation for a subject to be exposed to over long periods of time. The researchers’ goal was to create new imaging that would allow researchers to view the whole body in real time, and SIP-PACT was born.
"Photoacoustic imaging has been highly expected to get real-time whole-body imaging of a small animal with rich functional information," said Junjie Yao, assistant professor of biomedical engineering at Duke University. "With this advance, researchers can easily watch as drugs are distributed throughout an animal and track how different organs respond."
Photoacoustic imaging uses light to induce cells to emit ultrasound waves. Advances in the technology now allow it to scan entire cross-sections of a live mouse in real time for an entire body view in under a minute. (Duke University)
Photoacoustic imaging combines many different imaging techniques in one platform. It uses powerful, short laser bursts to safely cause cells to emit ultrasound waves that travel back through the tissue.
The result of this is a new imaging technique that can view up to five centimeters into biological tissue with a sub-millimeter-level resolution while retaining functional information that is usually provided by traditional microscopy.
"This penetration range enables functional imaging of whole bodies of small animals. This capability is expected to enable all kinds of biological studies in small animals and to accelerate drug discovery," said Lihong Wang, the Bren Professor of Medial Engineering and Electrical Engineering at CalTech and a collaborator on the paper.
In the recently published paper, researchers have added speed and panoramic views to the imaging technology that was highly sought after. They have added a circular ultrasonic detector and data acquisition system that can triangulate origin of an ultrasonic wave in the body of a small animal. The upgraded device could image a full cross section of an adult rat 50 times per second. This provides detailed videos of the inner working of the animal with 120-micrometer resolution.
"This approach is especially powerful because it does not rely on the injection of any type of contrast agent," said Yao. "You can be sure that changes are not caused by foreign variables. We think that this technology holds great potential for both pre-clinical imaging and clinical translation."
This paper was published in Nature Biomedical Engineering. It was supported by the US National Institutes of Health.
