Sonic flashlight gives users a new form of ultrasonic vision

A ‘sonic flashlight’ developed by a biomedical engineer at the University of Pittsburgh makes the human body seem translucent right in front of your eyes.

The prototype device is said to merge the visual outer surface of a patient’s skin with a live ultrasound scan of what lies beneath. It creates the effect of a translucent ultrasound image floating in its actual 3-D location within the patient, showing blood vessels, muscle tissue, and other internal anatomy.

‘In the practice of medicine, the standard method of viewing an image is still to examine a film or screen rather than look directly into the patient,’ said George Stetten, M.D., Ph.D., assistant professor of bioengineering.

Doctors currently use ultrasound to guide invasive procedures, such as inserting a needle in a vein. But to do so, they must look away from the patient at an ultrasound display screen, causing a displaced sense of hand-eye co-ordination.

Previous attempts to fuse medical images with direct vision have been largely unsuccessful, largely because of their complexity. Some have tried using miniature video cameras mounted on a headpiece. Others have used an approach similar to Stetten’s but requiring the user to wear a tracking device to determine viewer location.

Stetten is said to have eliminated the need for tracking devices and transmitters by taking full advantage of the way in which a translucent mirror superimposes images from both sides of the glass.

He positions an ultrasound scanner and the ultrasound display on opposite sides of a half-silvered, translucent mirror. The viewer looks through the mirror to see the patient and the ultrasound scanner positioned on the patient’s skin. At the same time, the ultrasound image is projected on the viewer’s side of the mirror in alignment with the corresponding location within the patient’s body.

This makes the ultrasound image appear to occupy the same physical space as the body part being imaged. If the viewing angle changes, the combined images remain true. The effect relies on precise geometric relationships between the ultrasound slice being scanned, the monitor displaying the slice, and the mirror.

‘We are actually merging the virtual image in 3D with the interior of the patient,’ Stetten said. ‘The reflected image is optically indistinguishable from the corresponding space within the patient.’

The result is an image within the natural field of view that can be used to guide invasive procedures, such as taking blood samples without missing the vein, or doing needle biopsies, amniocenteses, catheterisations or surgery.

Stetten named the process ‘tomographic reflection’ and the device a ‘sonic flashlight.’ Stetten has also built a portable sonic flashlight that could make it easier and more convenient for routine use in a doctor’s office. Both the stationary and portable devices will need to be refined and tested in the laboratory before being tested in the clinic.