Through a clever combination of two imaging modalities, scientists from Caltech and USC have developed a new technique that can quickly provide 3D color images that capture both the structure of soft tissues and details of how the blood vessels are functioning. The researchers have used the new technique to successfully image multiple parts of the human body. The method holds promise for enhancing breast tumor imaging, monitoring of nerve damage caused by diabetes, and brain imaging, among other applications.
The team describes the new technique in a paper that appears in the January 16 issue of Nature Biomedical Engineering.
Traditional ultrasound provides structural information quickly and inexpensively, but it has a limited field of view and only shows morphology in two dimensions. Meanwhile, photoacoustic imaging, has somewhat opposite benefits and challenges. It involves sending laser light into the body and measuring the sound waves that come out. It helps physicians and researchers see molecules in the vasculature in optical color—allowing for visualization of how blood is flowing through veins and arteries. However, photoacoustic imaging is insufficient when it comes to structural detail.
Other imaging tools such as computed tomography (CT) scanning and magnetic resonance imaging (MRI) have their own drawbacks: They require contrast agents, are expensive, involve the use of ionizing radiation, or are too slow for repeated regular use.
Enter RUS-PAT (rotational ultrasound tomography, RUST, combined with photoacoustic tomography, PAT). Lihong Wang, the Bren Professor of Medical Engineering and Electrical Engineering and the Andrew and Peggy Cherng Medical Engineering Leadership Chair at Caltech, developed PAT more than 20 years ago. Through PAT, molecules in the tissue that absorb optical light are imaged because they begin to vibrate when hit with pulsed laser light, generating acoustic waves that can be measured and converted into high-resolution images.
Wang, who is also the executive officer for medical engineering at Caltech, says his group’s aim with the current work was to combine the benefits of PAT with ultrasound. "But it’s not like one plus one," he says. "We needed to find an optimal way of combining the two technologies."