Photoacoustic imaging shows a mouse brain at work

Researchers at Duke University and CalTech have demonstrated a new method that combines light and ultrasound to peer inside living bodies and see intestines at work, flowing blood and neurons firing in the brain. 

The technique, called single-impulse photoacoustic computed tomography (SIP-PACT), uses extremely fast bursts of intense laser light to cause cells as much as 5 centimetres below the skin to ring like tiny bells, emitting ultrasound which is then recorded and used to form an image. The short duration of the pulse ensures the cells are not damaged. 

While SIP-PACT has limitations, such as the 5 centimetre depth limit, it also has several advantages over other techniques. Cells’ response to the laser pulse contains colour information that would be lost by ultrasound, for instance, and SIP-PACT is faster and involves less cumbersome equipment than magnetic resonance imaging (MRI), and does not require exposure to potentially harmful radiation as X-rays and positron emission tomography (PET) do.

The device the researchers have built can take 50 full cross-sections of an adult rat per second and resolve details down to 120 micrometres. This speed and resolution, says co-author Junjie Yao of Duke University, mean “researchers can easily watch as drugs are distributed throughout an animal and track how different organs respond”. 

The results are published in Nature Biomedical Engineering.