Imagine you have a medical emergency, you need a surgery but the doctor is hundreds of miles away. Now telesurgery comes to your aid. Telesurgery is the provision of providing surgical care over a distance with direct, real time visualization of the operative field with the help of telepresence technology and force feed back.

Types of Technologies:

 Telesurgery can be classified into several subgroups. They are:
1. Telepresence surgery: This technology uses a computerized interface to transmit surgeon’s actions at a surgical workstation to a remote surgical unit. This is done with the help of a unit at the remote site with haptic input to transmit to the surgeon the tactile environment at the remote site.
2. Telerobotics surgery: This technology uses a remote manipulator to transmit surgeon’s actions to the surgical unit. The difference between telerobotic surgery and telepresence surgery is that in telerobotic surgery there is no haptic feedback.
3. Telementoring: This is the technology in which an experienced surgeon observes and corrects a remote inexperienced surgeon by using interactive video.
 

Telepresence Surgery.

 Telepresence owes its origin to the need for handling dangerous and hazardous materials. In telepresence surgery there is a multisensory input that recreates the remote visual, auditory, and tactile environment at the remote site at the surgeons end. This allows the surgeon to feel physically present at the remote surgical site in terms of sensory input and ability to manipulate objects. The perception of distance is erased, and the surgeon can act in a locally recreated environment that is in fact an illusion.
 One of the most important aspects of telepresence surgery is movement scaling. Using mathematical models and techniques the surgeon’s hand and body movements can be scaled down at the remote surgical unit. This helps in scaling down hand tremors of the surgeon at the surgical unit. For example a 10cm hand movement of the surgeon can be scaled down to 1cm movement of the remote robotic arm.

Equipment

 In telepresence surgery robotic arms reproduce surgeons hand motions from the surgical workstation to the remote surgical unit. This is accomplished as the surgeon’s fingers and hands are placed into the rings of actual surgical instruments, which do not have actual tips as the original instruments. These rings are connected to motors, gears and other mechanical devices. They translate surgeon’s hand and finger movement into digital signals. These signals are transmitted through a computer and transmission links to the robotic arms at the remote surgical unit.

 The major components of this equipment are discussed below.
1. Human computer interface (HCI): This component consists of control mechanisms and feedback mechanisms. The control mechanisms can be joystick, mouse, data glove, etc. The feedbacks that are provided are data feedback, force feedback, tactile feedback, olfactory feedback (using electronic nose), etc.
2. Computer: Computer helps in downscaling surgeons movements to filter out tremors and steady erratic movements. Different computers can be used for master-slave control and feedback like tactile feedback, auditory and visual feedback, etc.
3. Communication links: Long distance communication is the most crucial and critical element in telesurgery. The signals that are communicated are audio, 3D video, tactile, instrument readings, etc. The surgeon needs accurate and continuously updated signals to perform surgery. The main parts of the communication channel are  a) satellite, b) microwave links, and c) fiber optic cables. The data is transmitted at about 90Mbps and audiovisual information accounts for most of this band width.
4. Remote surgical site components: There are several robotic arms that hold the tools, end effectors, cameras, tactile feedback sensors built into the robotic arms, etc. There are assistants and nurses at the remote site to change the tools.

Visual Feedback:

The visual feedback system consists of digital cameras at the remote surgical unit and 3D glasses and monitors at the surgical workstation. The surgeon wears the 3D glasses to get a 3D perspective of the remote surgical unit. The visual environment of the surgical workstation should resemble that of the remote surgical unit. This is accomplished by projecting the image from the surgical unit onto a mirror directly over the surgeon’s hand and control rings. The projected image displays the instrument tips as if they were at the end of rings in the surgeons hand. This is the way in which the remote surgical unit is recreated at the surgical workstation.

The whole system can be modeled as in the following diagram.

Force FeedBack:

 In human body the muscles, joints, and tendon receptors determine the force and torque acting. In telesurgery the force acting at the remote surgical site can be sensed in many ways. Some are given below.
     By using strain gauge bridges in the wrist of the remote manipulators.
     By using position sensors.
     By using hydraulic actuator pressure differentials.
     By using small servomotors.

Of all the methods servomotors are used in telesurgery. Force sensing in telesurgery is done in the following way. As resistance is encountered at the remote surgical unit, like when the tip of the suture needle passing into tissue more dense than the initial subcutaneous tissue, signals are generated at the servomotor mechanism and these signals are instantly fed back to the surgical work station where the surgeon is located. The servomotors are connected to the instrument rings in the surgeon’s hand. These servomotors recreate the same amount of resistance that is encountered at the remote surgical unit at the instrument rings in the surgeon’s hand.

 The ability of humans to perform complex tasks like telesurgery depend on their sensory perception, motor control and decision making capabilities. The human couples decision-making and motor control functions with the remote manipulator in telerobotics. In telesurgery all the sensations that exist in the remote surgical unit should be fed back to the surgeon. This improves the dexterity, reliability and ease of the complete process of telesurgery.

 Tactile Sensors:

In telerobotics currently vision provides most of the feedback. But for some applications like telesurgery direct vision is not possible, though there is remote viewing using cameras and television, tactile feedback becomes significant. For effective tactile feedback we need a teletouch system to mimic human tactile sensing capability at the remote site and to display the information back to the human. The remote manipulators should be equipped with tactile sensors similar to human tactile sensors.

 The important characteristic that a tactile sensor should have in telesurgical applications are:
     The spatial resolution should be approximately same as that of the human fingertip
     It should be able to detect forces of magnitude as small as 5mN.
     It should have high sensitivity for small forces eventhough the viceversa may not be needed.
     It should be wear resistant especially with slip.

Some sensors that could be used in telesurgery are piezoresistive sensors, peizoelectric sensors, inductive sensors, capacitive sensors, optoelectronic sensors, etc. A peizoelectric sensor is shown in the figure below.  It is called the multi-element stress rate tactile sensor. It provides transient event information at the finger-object interface. This sensor consists of piezoelectric polymer strips molded into the surface of the rubber skin covering the robot fingertip. These piezoelectric elements provide localized information important to manipulation control.

The sensor has the ability to detect the following three parameters. a.) Very light contact forces, which can be detected for signaling transitions between position and force control. b.) Local skin curvature information, which provides contact shape and area. c.)Incipient slip, which is generated by small micro slips prior to gross slip. The photograph of the Multi-element Stress Rate Sensor is shown in the next page.

Muiti- element Stress Rate Tactile Sensor

Kinesthetics:

Kinesthesia is the sensation of movement or strain in muscles and tendons of the human body. The major role of kinesthesia is sensing and controlling contact between the body and external environment. Although tactile sensations play a major role in sensing and control of contact force, kinesthesia plays the major role in sensing and control of the force in techniques like telesurgery where a tool is used. Kinesthetic sensation involve bi-directional energy flows, i.e. energy flows from the human to the environment and from environment to human. So to sense the environment means to modify the environment.

 In telepresecne surgery kinesthetic display is achieved by using the following principle. The remote arm at the surgical unit is moved the same amount as the hand of the surgeon and the force developed at the surgical unit is measured and used as the force feedback signal. The main characteristics of a kinesthetic display system are:
     It should accurately reproduce the forces intended to be applied
     It must have sufficient band width so that transients due to contact making and braking should be reproduced exactly.
     It must allow uninhibited movement of the surgeon’s hand when no force feedback is meant to be conveyed.

Kinesthetic Display Model:

 For kinesthetic display in telesurgery we have sensors that sense the force applied at the remote surgical unit by the robot arm. These sensors are servomotors that develop signals when any change in velocity is encountered. This is how they detect the force that is applied by the robotic arm at the surgical unit.

 Since the servomotors detect velocity to determine the force applied the stiffness play a crucial role. There are no material that does not change shape when forces are applied. So we have to include loss due to stiffness also in our model. Then there is friction at the remote robotic arm that does the surgical task. This friction will  cause some loss in the force being detected. There are three types of friction coming into play. They are static friction, viscous friction and kinetic friction. Of these viscous friction plays a major role as its value changes with velocity and here we measure force by measuring change in velocity. Friction is inherent in the system and so we can’t avoid them.

 The forces are detected by servomotors which are machines and machines doesn’t have 100% efficiency. So there are some losses inside the servomotor which can’t be avoided. These losses happen at both remote surgical unit and surgical workstation. The signals developed by the servomotors are send over a large distance using satellites and microwave links. The signal transmission over a long distance causes communication losses.

 The detected force is applied at the surgical workstation by servomotor on the rings that remain in the hands and fingers of the surgeon. These rings have mass and there is a loss associated with this mass as well. We have to incorporate this loss as well in our final model.

 Taking the above factors into consideration we can reach the conclusion that in telesurgery the following equation doesn’t hold good,
Fs = Fr
Where Fs is the force experienced by the surgeon and Fr  is the force detected at the remote surgical unit. We can say that the equation for this kinesthetic display system is:

Fs = Fr – (Losses) ------- (1)
Losses = K*dx + Lsr + dc + Lss + F(x,v) + Mv ---------- (2)
Where K is the stiffness, dx is the elongation of the link when force is applied, Lsr is loss at the surgical unit servomotor, Lss is the losses at the workstation servomotor, dc is the communication losses, F(x,v) is the viscous friction losses, M is the mass of the rings in the surgeons hand and v is the velocity.
So the final mathematical equation for the kinesthetic display of the telesurgical task is

Fs = Fr – (K*?x + Lsr + ?c + Lss + F(x,v) + Mv) --------- (3)
The kinesthetic display that could be used in telesurgery is modeled as in the diagram.

The components are
1. Remote surgical unit
2. Servomotor at the remote surgical unit
3. Servomotor at the surgical workstation
4. Rings and instruments in the surgeon’s hand
5. Surgeon