Researchers have developed a technique for in vivo super-resolution photoacoustic computed tomography (PACT) that breaks the acoustic diffraction limit by localizing the centers of single dyed droplets flowing in blood vessels. This technique has been shown to resolve brain blood vessels at a sixfold finer resolution.
Photoacoustic computed tomography (PACT) is a noninvasive hybrid imaging technique that excites biological tissues with light and detects the subsequently generated ultrasound to form images. PACT combines the advantages of both optical imaging – high optical contrast and ultrasonic imaging – high resolution and deep penetration in biological tissues. PACT has been widely used for vascular network mapping, functional brain imaging, and tumor detection in deep tissues.
The researchers fabricated photoacoustically bright oil-in-water droplets using a solution of a hydrophobic dye, namely IR-780 iodide in oil. The sizes of the droplets range from 4 to 30 microns, which are much smaller than the wavelengths of the detected ultrasound, making them excellent photoacoustic point sources. Taking advantage of their small sizes, liquid compliance, and high photoacoustic brightness, once injected into the bloodstream, the droplets flow smoothly in blood capillaries and provide excellent tracers for localization-based super-resolution imaging. Superresolution PACT of microvasculature has the potential to substantially advance the study of normal blood-vessel function, as well as disease, such as angiogenesis in tumors in deep tissue.