For doctors specialising in fine-scale surgery, such as operating inside the human eye or repairing microscopic nerve fibres, freehand tremors can pose a serious risk for patients.
By harnessing a specialised optical-fibre sensor, the new tool reportedly makes corrections at a rate that is quick enough to keep the surgeon’s hand on target.
According to a statement, researchers from the Johns Hopkins University (JHU) Whiting School of Engineering and Johns Hopkins School of Medicine in Baltimore, Maryland, have combined the optical coherence tomography (OCT) imaging technique as a distance sensor with computer-controlled piezoelectric motors to actively stabilise the tip of a surgical tool.
A paper describing the new device, named SMART (Smart Micromanipulation Aided Robotic-Surgical Tool), has been published in the Optical Society’s open-access journal Optics Express.
‘Microsurgery relies on excellent motor control to perform critical tasks,’ said Cheol Song, a postdoctoral fellow in the Electrical and Computer Engineering Department at JHU. ‘But certain fine micro-manipulations 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.
Various optomechatronics techniques, including robotics, have been developed to help augment stability and minimise the impact of hand tremors.
None so far have been able to merge optic-optic rapid and fine-grained sensing with handheld automated surgical tools.
According to JHU, the major challenge for researchers has been finding a way to precisely measure and compensate for the relative motions of a surgical instrument in relation to the target.
OCT attracted the attention of the researchers because it is said to have higher resolution (approximately 10 microns) than either MRI or ultrasound. It also uses eye-safe near-infrared light to image tissues.
To apply this imaging technique to its work, the research team 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 optic-optic-based common path OCT (CP-OCT) technique is said to have provided the capability; the optical signal of this sensor uses the same path, or optical fibre, to transmit and receive the near-infrared light.
Because this single optic-optic cable is small and flexible, the researchers could integrate it into the front of a tool used for eye surgery.
By continually sending and receiving the near-infrared laser beams, the high-speed optic-optic sensor precisely measures the motion of the probe.
This information then feeds to a computer that sends signals to small piezoelectric motors integrated into the surgical device to control the position of the tool tip.
This creates a series of ‘station-keeping’ manoeuvres that compensate for the surgeon’s hand tremors.
Combined, the sensor and the motors can operate accurately at 500Hz compared with the typical tremor frequency of 0–15 hertz.
The researchers compared the effectiveness of the system by testing its ability to compensate for hand tremors during five- and 30-second intervals.
According to the researchers, these time periods were sufficient to determine the different characteristics between short- and long-term hand tremors.
‘A 30-second time period is enough to evaluate a surgeon’s basic physiological hand tremor characteristics,’ said Song. For complete characterisation, however, a record of a full surgical procedure, which typically lasts more than three hours, will be needed.
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