Ultrasound adaptation puts real and sonic images at operator's fingertips

SIR meeting provides forum for discussion

A handheld ultrasound device developed by researchers at the University of Pittsburgh merges the patient, image, instrument, and operator's hands into a single field-of-view without the need for a head-mounted display.

Dubbed the Sonic Flashlight, the device uses a mirror to combine real-time ultrasound images with a real-world image of the patient, creating the illusion that the body part being examined is translucent.

Accessing vessels and fluid collections is made more intuitive, especially to the novice user, said Dr. Wilson Chang, a visiting scholar at Pittsburgh, who spoke March 27 at the Society of Interventional Radiology meeting in Phoenix.

Viewing the image in the context of the body eliminates the sense of hand-eye displacement that occurs when the operator must look away from the patient to view an ultrasound monitor. This raises the potential that the Sonic Flashlight will make it easier to accurately place vascular access catheters, drainage catheters, and biopsy needles, Chang said.

Researchers at Pittsburgh have been developing the Sonic Flashlight for three years. The current version consists of a Terason 10-MHz scanner modified by the attachment to the transducer of a small flat-panel display and a 20 x 50 x 1-mm half-silvered mirror. The image on the monitor is reflected precisely at the proper location within the patient.

The patented device, developed with funding from the National Institutes of Health, National Science Foundation, and Whitaker Foundation, superimposes the ultrasound image in real-time on the patient, while merging the operator's hands and any invasive tools in the field-of-view. The result of this process, which the researchers call real-time tomographic reflection, is a virtual image of the outer surface of the patient, obtained visually, with a simultaneous ultrasound image of the patient's interior. Rather than having to look away from the patient to an ultrasound monitor, the operator looks directly at the patient and sees through the skin to the underlying tissue, as if the body were translucent.

To test how the device might perform under actual conditions, Chang and colleagues enlisted 20 medical staff with little or no ultrasound experience to use the Sonic Flashlight to perform simulated invasive procedures. Each used a 21-gauge needle to pierce the lumen of a vascular access phantom. The time from touching the transducer to piercing the lumen was recorded.

The procedure was repeated using the Site-Rite, a small battery-powered ultrasound scanner in routine practice to assist physicians in accessing arteries and veins. Significantly faster times were recorded using the Sonic Flashlight for guidance as compared with the Site-Rite (5.17 versus 6.54 seconds). Several subjects stated that the product made more sense or was more intuitive.

"The results of this study suggest that learning to use the Sonic Flashlight for guidance is significantly easier than learning to handle conventional ultrasound systems," Chang said.