An ultrasound probe about the size of a grain of rice that could offer panoramic views from inside the human body is being tested by US researchers. They say it could be threaded through blood vessels in the brain or swallowed like a pill.

The new device – about 1 millimetre across, 1 millimetre long and shaped like a hexagonal cylinder – affords a panoramic picture, showing the view from each side of the device, and to the front.

"All the commercially available units can only look to one side or ahead," says Chen. "We can look out the front and all sides simultaneously."