Novel Surgical Tool Eliminates Freehand Tremors

The feedback control loop used the fiber-optic based common path OCT (CP-OCT) technique, which uses the same path, or optical fiber, to both transmit and receive the near infrared (IR) light.

Because the single fiber-optic cable is small and flexible, the researchers were able to integrate it into a surgical tool used for eye surgery. By continually sending and receiving the near IR laser beams, the high-speed fiber-optic sensor precisely measured the motion of the probe. This information was then fed to a computer that sent signals to small piezoelectric motors integrated into the surgical device to control the position of the tool tip. Combined, the sensor and motors operated accurately at 500 Hz, much higher than the typical tremor frequency of 0-15 Hz. The feedback loop created a series of “station keeping” maneuvers that compensated for the surgeon’s hand tremors.

The researchers then compared the effectiveness of the system by testing its ability to compensate for hand tremors during 5- and 30-second intervals. The tests were performed on two targets; the first was a dry “phantom,” a material that has sufficient properties to stand as a proxy for medical research. A more real-world test was also done on a viable chicken embryo, which better simulated a realistic surgical environment because of the unpredictable movements of the live embryo. The study describing the SMART tool was published in the October 2012 issue of Optics Express.

“Microsurgery relies on excellent motor control to perform critical tasks,” said lead author Cheol Song, PhD, a postdoctoral fellow at the JHU Electrical and Computer Engineering Department. “But certain fine micromanipulations remain beyond the motor control of even the most skilled surgeon. At its most steady, the human hand naturally trembles, moving on the order of 50-100 microns several times each second.”

OCT is an optical signal acquisition and processing method that captures micrometer resolution three-dimensional (3D) images from within optical scattering media such biological tissue. The use of relatively long near IR wavelength light allows it to penetrate into the scattering medium. OCT has a higher resolution (approximately 10 micrometers) than either magnetic resonance imaging (MRI) or ultrasound. Since the laser output from the instruments is low, damage to the biological tissue is not likely.

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