A laser hits tissue, and the tissue responds with a barely audible click — a sound wave. Sensors pick it up, and from that, an image of what's inside is built. That's how photoacoustic imaging works: light reaches deep, and sound carries the picture out.

In the new scheme, there are no sensors. Instead, several thin light beams are sent through the area where the wave has passed. The sound slightly jiggles the air or tissue, and the beams deflect — like a straw in a glass when the water is disturbed. That deflection is the signal.

First, the deflections are used to reconstruct a map of pressure gradients, and then the pressure itself. The result is an image without a single microphone. The authors believe this method is more sensitive and distorts the signal less than conventional sensors.