BALTIMORE – A new “smart” surgical tool uses a specialized optical fiber sensor to compensate for almost imperceptible hand tremors by making hundreds of precise position corrections per second – fast enough to keep a surgeon’s hand on target.
Even the most skilled and steady surgeons experience tiny hand tremors when performing delicate tasks. Normally inconsequential, but for doctors specializing in fine-scale surgery such as operating inside the human eye or repairing microscopic nerve fibers, freehand tremors can pose a serious risk for patients.
Researchers from the Johns Hopkins University Whiting School of Engineering and Johns Hopkins School of Medicine combined optical coherence tomography as a distance sensor with computer-controlled piezoelectric motors to actively stabilize the tip of a surgical tool. They dubbed their new device SMART (smart micromanipulation-aided robotic-surgical tool).
“Microsurgery relies on excellent motor control to perform critical tasks,” said Cheol Song, a postdoctoral fellow in the electrical and computer engineering department at Johns Hopkins. “But certain fine micromanipulations remain beyond the motor control of even the most skilled surgeon.” At its steadiest, the human hand naturally trembles, moving on the order of 50-100 µm several times each second.
Various optomechatronics techniques, including robotics, have been developed to help augment stability and minimize the impact of hand tremors. None so far has been able to seamlessly merge simple fiber optic rapid and fine-grained sensing with handheld automated surgical tools. A challenge for researchers has been to find a way to precisely measure and compensate for the relative motions of a surgical instrument in relation to the target.
The imaging technique OCT attracted their attention because it has higher resolution (approximately 10 µm) than either MRI or ultrasound. It also uses eye-safe near-infrared light to image tissues.
To apply it to their work, the team members first had to integrate an OCT-based high-speed, high-precision distance sensor directly into a small, handheld surgical device. The device could then hold a variety of surgical instruments at the tip, such as a scalpel or forceps. The well-known fiber optics based common path optical coherence tomography (CP-OCT) technique provided the essential capability. As its name suggests, the optical signal of this sensor uses the same path, or optical fiber, to both transmit and receive the near-infrared light.
Because this single fiber optic cable is so small and flexible, it could easily be integrated into the front of a tool for eye surgery. By continually sending and receiving the near-infrared laser beams, the high-speed fiber optic sensor precisely measures the motion of the probe. This information is fed to a computer that sends signals to small piezoelectric motors integrated into the device to control the position of the tool tip, creating a series of “station keeping” maneuvers that compensate for the surgeon’s hand tremors.
The sensor and motors combined can operate accurately at 500 Hz (500 times each second), which is much higher than the typical tremor frequency of 0 to 15 Hz. The effectiveness of the system was compared by testing its ability to compensate for hand tremors during 5- and 30-second intervals. “A 30-second time period is enough to evaluate a surgeon’s basic physiological hand tremor characteristics,” Song said. For complete characterization, however, a record of a full surgical procedure, which typically lasts more than three hours, will be needed.
For the study, 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.
During the next few years, the researchers hope to take their instrument from the laboratory to the operating suite and, with additional refinements, expand its use to other fine-scale surgeries.
“The main objective of our research has been to make an established surgical tool ‘smarter’ by incorporating fiber optic sensors and motion control to allow surgeons to maneuver the tool tip precisely and safely,” said Jin U. Kang, another researcher with the electrical and computer engineering department at Johns Hopkins. “SMART, which is capable of fine motion control and sensing, could significantly enhance the surgical performance of doctors and minimize surgical accidents.”
The work was published in the Optical Society’s open-access journal Optics Express