Surgical robotics is a very diverse field. So in this topic we give a broad introduction to different aspects of robotics. These include the description of state-of-the-art systems, having a look at safety aspects and looking at new research. In general, surgical robots are not intended to replace surgeons, but rather to assist them.
State-of-the-art
A surgical robot can be defined as a "powered computer-controlled manipulator with artificial sensing that can be reprogrammed to move and position tools to carry out a range of surgical tasks". These robots in general consist of an arm(s) that is made up of links and joints and surgical tools can be attached at the end-effector of the robot. The robots are computer-controlled so that the end-effector can move to any desired location within the workspace. To complete the robotic system, intraoperative imaging as well as registration methods are included. This is because to be able to move accurately, the robot has to be aligned relative to the patient. Lastly the surgeon also needs additional displays to show the treatment plan as well as the actual position of the robot and the surgical tool. This display should only show basic schemas in general to not distract the surgeon during surgery. However during emergency situations the display should show detailed information about the patient and the robot.Due to the additional actor in the OR, the preplanning now also can include a simulation of the movement of the robot to make sure that the end-effector reaches the desired location and doesn't harm people or other instruments in the process. [1] [2]
Advantages and disadvantages
Up to now the use of surgical robotics enhibits advantages and disadvantages. During surgery the robots provide a higher accuracy compared to manual methods. This is extremely helpful for procedures with small working areas or surgeries in a sensitive area of the patient. Furthermore robots can reproduce their tasks without loss of accuracy and they can hold a fixed position for a long time without movement. However the use of robots is still expensive right now and raises the question of safety and responsibility, which are not regulated yet. Another drawback of some (telemanipulating) robotic systems is the lack of feedback. While the surgeon can see the position of the tool in the patient, he rarely gets additional information, as velocity or acceleration of the robotic arm. [1] [2]
Classification
Different classifications for surgical robots exist. According to a classificiation from Taylor, they are grouped into the following classes, which divide the systems depending on the work they are doing:
- intern replacement: These systems perform tasks, that are normally performed by other people to assist the surgeon (i.e. for retraction).
- telesurgical systems: Here, the motions of the robot are specified by the surgeon through the use of a joystick or similar devices. This could lead to surgeons operating from far distances. For example performing a surgery in an OR in Munich from a control device in Stockholm.
- navigational aids: These robots deliver aid to the surgeon by displaying accurate positioning of the surgical tools.
- precise positioning systems: These systems are used to fix a tool guide into accurate positions so that the surgeon can then insert surgical tools correctly according to the surgical planning.
- precise path systems: Here, the robot follows predefined paths wiht a high accuracy (i.e. for laser resection of tumors) and can help to prevent surgical tools from entering a forbidden room in space. [3]
Another approach classifies surgical robots into:
- supervisory-controlled: These are robots that execute preplanned motions/tasks while being watched by the surgeon. The surgeon can still interfere if necessary.
- telemanipulators: (see a few lines up)
- shared control: Here, the surgeon directly controls the movement of the robot and the robot improves the surgeons work by counteracting physiological tremor, among others. [4]
Examples of some types will be described later on.
Design
In the beginning of the developement of surgical robots, conventional industry robots have been used to perform tasks and be used in research. However the surgical environment demands special features. Therefore, robot designs have been developed that aim to be used in the surgical environment. Industrial robots act inside a cage. This cage is not available during surgery, so the movement of the robot has to be restricted in other ways. Mechanically, one way is to hav a passive wrist that moves closely around the planned insertion point. Another method includes constraints so that the robot arm moves around the remote center of motion and far enough away from the rest of the robots structure. Robots in surgery are often used for procedures in small spaces, so these systems should also allow for high dexterity in small spaces. To achieve this, cable actuated wrists or bendable elements can be used. Last but not least the robot is supposed to assist the surgeon, so in cases of unexpected change of the plan, the surgeon should still be possible to move the robot out of the workspace if not needed. Other possibilities include moving parts of the robot arm but keeping the end-effector in a fixed position. [6]
Figure 1: robot motion path (right) and its accuracy (right) in the surgical field [16]
Autonomy
Most surgical robots up to now are autonomous up to a certain degree, meaning that they don't perform tasks on their own with own planning and changing. Determining the possible autonomy of a robot consists of three factors: mission complexity, human independence and envirnomental difficulty. The first and third factors are extremely complex for the surgical environment. Furthermore a human independence will be hard to implement because surgeons are not eager to give away their abilities and performances during surgery. One factor to increase autonomy however, is to evolve learning for movements. This can be done by either mathematical computations or by manually moving the robot preoperatively. To make the movement learning more effiicient, the Language of Surgery Project has been developed. In there, complex motions are cut into smaller segments to simplify learning and computation. [7]
Figure 3: schema of the movement division [7]
Types
The following link provides an overview of existing (2005) surgical robotic systems (click here). Some will be described more detailed below.
NeuroMate: This is a multi-joint one arm robot used to perform stereotactic neurosurgery and in frameless ultrasound registration. The position information is obtained by potentiometers measuring the angle in each joint. The computer software, that also receives the position information, controls the robot movement, the registration and the procedure planning. This system is FDA-approved and already used in some clinics. [10]
Figure 4: NeuroMate robot [17]
NeuRobot: This robot is a telemanipulator, used for example for the removal of tumor portions. It consists of a micromanipulator, a manipulator-supporting device , an operation-input device and a 3D display monitor. The micromanipulator is a microscopically guided manipulator combined with surgical tools. The manipulator-supporting device is a robotic arm made out of several joints whose positions can be controlled. The operation-input device controls the input forces, activated by the surgeon through the movement of three levers on the working station. And finally the 3D display monitor is used by the surgeon to see/control his work. [11]
Figure 5: A) whole NeuRobot system, B) tip of the manipulator with surgical tools [18]
NeuroArm : This system combines a robot, a controller and a workstation to perform different tasks, also by being able to put different tools on the endeffector. It's based on the master-slave principle and uses MR images for planing and intraoperative images. The robot consists of two arms with 7 degrees of freedom (DOF) for tool positioning and a 1 DOF mechanism at the end-effector for tool actuation. The workstation provides visual, audio and tactile feedback. [5]
Figure 6: NeuroArm for microsurgery (left), stereotaxy (middle) and its workstation (right) [5]
ROSA: This is a precise positioning system. It is used to improve the accuracy of incision points during treatment. Therefore the robot consists of a 6-joint arm on one mobile base and a navigation camera on another mobile base. After 2D intraoperative imaging-based trajectory planning is performed and the registration is done, the robotic arm takes the preplanned position. On its end-effector it has a tool holder guide. This allows the surgeon to position conventional surgical tools during the tratment with high accuracy through the tool holder. Trajectories can be adjusted to possible movement of the patient due to real-time imaging. This robot has an assistant function and the surgeon is performing all tasks manually. [12]
Safety aspects
Enhancing safety
On the one hand, the use of surgical robotics can increase the safety during surgery. Robotic systems can provide a higher accuracy when performing tasks which can increase safety especially when working in small and sensitive areas. Furthermore robots don't loose attention due to being tired, which in contrast could lead to negligent work from humans. Additionally the implementation of forbidden zones for the end-effector in the workspace can increase safety for the patient as well as for the staff inside the OR.
Decreasing safety
On the other hand people are safety critical regarding robots in the OR, because the usage of cages, as for industrial robots, is not possible in an surgical setting. Due to the critical environment, the robot should enhance redundancy, so that one failure doesn't cause a collapse of the whole system. Furthermore the registration is an important step to assure safety. The model environment has to correspond accurately to the actual environment, otherwise planned movements/actions can lead to harming the patient, the staff or the robot itself.
The fact that there exist no specific regulations for medical robotics yet decreases the ability to formally test the safety of these systems. Recommendations have been proposed but they are not used extensively. In contrast, regulations for conventional surigcal equipments are used, even if they are not accurate for surgical robotics. This area still has to be approved to enable formal testing and checking procedures.
To ensure the afe working of a surgical robot, many types include a safe-fail control, so that in case of an error/failure, the robot shuts down in a safe and predictable manner. To do so, different safety concepts can be applied. One is shown on the right, which is based on the "Failure Mode and Effect Analysis" (FMEA), which identifies all possible failures of the system components in a systematical manner.
Figure 8: Safety Concept in multiple layers [15]
Research
Micro- and Nanorobotics
Nanotechnologie uses micro-electro-mechanical-systems (MEMS) to develope more efficient systems. Equipping robots with these technology can make them smaller, faster and more accurate. Furthermore it's possible to include sensors and actuators on a single instrument. A nanorobot therefore is a nanotechnological robot which freely diffuses in the human body and can interact with specific cells at a molecular level. This type of robot can be made up of carbon as a main element and a diamond coationg that prevents the robot to be attacked by the human immune system. Other types are made up of biocompatible materials that can degrade if the robots task is finished. These robots can get their power for movement from chemically powered motors (metabolizing local glucose and oxygen) or externally from magnetic, acoustic or ultrasound energies. The small computers are enough to provide necessary computation. Communication can be done for example via acoustic signaling and undegraded nanorobots can leave the human body through the excratory channels or by exfusion.
Nanorobots can be used for drug delivery, for example in cancer treatment. The small size and possible movement makes it possible to deliver drugs directly to the disease-affected cells, while sparing the healthy environment. This increases efficiency and decreases possible drug side effects. It can be even possible for nanorobots to deliver the drugs intracellularly by penetrating the cell membrane and therefore furthermore improving precision of the drug delivery. Another application filed is microsurgery. Due to their size, nanorobots can reach difficult areas in the human body, so that equipped with mirco-sized surigcal tools, they can perform surgical tasks even in regions that are hard-to-reach, for example via telemanipulation. An example for these tools are tetherless microgrippers. A last posssible task for nanorobots is to enhance disease diagnostics. By being equipped with different bioreceptors, the nanorobots can realize different biomolecular interactions while moving through the body. This can enable precise disease diagnostics and the robots can transport biological elements outside the patient if there is a need for further analysis.
A critical point for the use of nanorobots is the possibility of toxic reactions inside the body evoked by the nanorobots. So this aspect has to be kept in mind while deveoping and testing nanorobots.
Figure 8: possible propulsion mechanisms (left & middle) and example nanorobots (right).
From top to bottom:Magnetic helical for cargo delivery, microgripper, antibody-immobilized
for sensing of cancer cells, for biodetoxification [13]