Remotely touching tissue

Designers at Harvard University in the US have developed a means by which surgeons can remotely touch tissue during operations.

Researchers at Harvard University are developing remote palpation systems to convey tactile information from inside a patient’s body to the surgeon’s fingertips during minimally invasive procedures. These new instruments contain tactile sensors that measure pressure distribution on the instruments as tissue is manipulated. The signals from the sensors are sampled by a dedicated computer system, which applies the appropriate signal processing algorithms.

The tactile information can be conveyed to the surgeon through tactile `display’ devices that recreate the remote pressure distribution on the surgeon’s fingertips. Creation of remote palpation technology will increase safety and reliability in present minimally invasive procedures, and bring the advantages of minimally invasive techniques to other, more complex procedures, which are not possible today.

According to Harvard’s William Peine, the target application for the remote palpation technology is lump localisation in minimally invasive thoracic surgery. In this procedure, hard nodules in the lung must be localised for excision. This is trivial using traditional palpation with the fingers because the nodule is much stiffer than the surrounding lung tissue. Using minimally invasive techniques, however, the process can be frustrating and time consuming.

The development of a remote palpation instrument that maps the surgeon’s finger motions to the instrument tip while providing tactile feedback will decrease localisation times.

The instrument consists of a tactile array sensor on the instrument tip, a shape display against the surgeon’s finger, and a drive mechanism to couple the motions of the surgeon’s finger to the instrument tip.

Two prototype palpation instruments have already been constructed. One used a cable drive mechanism and worked with the pinch grasp motion of the surgeon’s thumb and index finger. The second was completely passive and used a pin joint at the sensor and a U-joint at the display.

Tactile sensations measured with the sensor are recreated on the surgeon’s fingertip with the tactile shape display. A universal joint connects the sensor to the main instrument shaft. This allows the sensor to level itself against the lung tissue despite the entry angle of the instrument into the chest cavity. The shape display is also connected to the main shaft with a pin joint. This allows the angle of the surgeon’s wrist to assume a natural angle.

The researchers also developed a control scheme to simulate compliant tissues using the shape display and an actuated positioner. The method modelled the mechanical interaction between the finger.

The tactile display in the prototype system consisted of a line of 10 individually actuated pins that were raised against the fingerpad. SMA wires were used to drive the pins. As electric current heats the wire, it goes through a phase transformation and shortens, thus pushing the pin up. With this design, each pin can move 3mm and produce over 1N of force. The slow response times of SMA was overcome by using water cooling and position feedback for each pin from optical sensors.

Harvard University: Tel: +1 617 496 9098