"Sonic Flashlight" Gives Users A New Form Of Ultrasonic Vision

The prototype device merges 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. This causes a displaced sense of hand-eye coordination.

"The difficulty in mastering these skills has motivated research into developing a more natural way to visually merge ultrasound images with the perceptual real world," Stetten said. His device enables the viewer to look directly at patients and see their internal anatomy.

Previous attempts to fuse medical images with direct vision have been largely unsuccessful, in part 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 an tracking device to determine viewer location.

Stetten has 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 strategically positions an ultrasound scanner and the ultrasound display on opposite sides of a half-silvered, translucent mirror.(Fig. 1) 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 perfect 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. Even if the viewing angle changes, the combined images remain true. The effect relies on precise geometric relationships (Fig. 2) between the ultrasound slice being scanne