Robotic devices have been used in the medical industry for more than 40 years. Despite the advantages, researchers have faced unique challenges in developing effective, safe robotics applications for medical use. In contrast with industrial applications in which robots operate in work cells where human staff is not permitted to enter, robots in the medical field must operate in direct contact with the patient and medical staff; therefore, the safety requirements are considerably more complex and restrictive than in industrial situations.
The field of neurosurgery presents a classic example of this challenge because it demands extremely high precision for positioning surgical tools during an operation. Robots can achieve considerably greater precision and repeatability than the most experienced neurosurgeon. However, they are unable to respond in an immediate and autonomous way to dangerous and unexpected events.
Haptic Devices for Neurosurgery
Because surgeons cannot delegate an entire procedure to a robot, the best robotic solution consists of a master/slave approach. The surgeon assigns movements to a robotic device, and then the robot moves the surgical instruments for precision positioning.
Because the master/slave approach physically disconnects surgeons from their own instruments, they can maintain a certain level of connection with the operating process through special sensors capable of reproducing all the characteristic sensations of a manual operation. These sensors, known as haptic devices, are capable of reproducing force sensations on the command device. This solution allows for a considerable increase in the safety conditions in which the robot operates because all of its movements are suitably controlled by the surgeon.
With more than 10 years of work with medical robotics and haptic master/slave robotic systems, Mechatronics (Padova, Italy) took on the challenge of developing a control system for a robotics application designed for minimally invasive neurosurgery operations. In this application, the surgical tool is a special device for tumor lesion therapy called the Photon Radio-Surgery System — ZEISS (PRS).
The PRS is a miniaturized source of low-energy x-rays that emits radiation from the end of a probe inserted in the cranial cavity. The PRS allows the surgeon to confine the dose of radiation to the tumor lesions and avoid contact with healthy regions of the cerebral tissue. The treatment is minimally invasive because the probe is passed through a hole that is only 3 to 7 mm in diameter. This involves considerable advantages in terms of patient trauma and postoperative recovery.
Previously, the surgeon had to manually control the PRS by positioning the device on a metal structure known as a stereotactic helmet (Figure 1). The emitting probe progressed through the cranial cavity via a rack coupling. The metal structure acted as a 3D reference for positioning the neurosurgical instruments. However, manual control did not offer high precision, and its efficacy in the application of the PRS was limited to spherical tumors, which are rare.
Linear Actuator for Neurosurgery (LANS)
The focus was on extending the PRS to patients with oblong tumor lesions, which are more common than spherical lesions. The dose would need to be distributed along the main axis of the lesion so the range of the radiation spheres could cover the entire tumor lesion. Due to the precision required to perform this movement, a robotic system was necessary for the application. As a result, the Linear Actuator for Neurosurgery (LANS) was developed.
The LANS is a robotic device designed to move the PRS source in a linear manner within a haptic master/slave procedure. The researchers used the NeuroMate, a commercial robot from the UK, as a spatial positioner for the LANS. This allows the source’s axis of progression to run along the main axis of the tumor lesion (Figure 2). The surgeon determines the probe’s movement within the cranial cavity.
Using the LANS, the surgeon can feel the forces interacting between the probe and the cerebral tissues and act accordingly. In addition, to improve the precision of the operation, a suitable virtual environment guides the surgeon during each phase of the operation.
CompactRIO for Automated Robotics Control
The control system of the entire haptic master/slave robotic system requires increased sturdiness and reliability in managing the surgical procedure. The first prototype was built with several homemade control devices, which guaranteed control redundancy and the essential safety conditions. However, the prototype had considerable limitations because it was bulky, lacked portability, and required a great deal of time to program the control and supervisory modules.
These challenges were addressed using a CompactRIO system and CompactRIO I/O modules from National Instruments (Austin, TX). The controller was built with CompactRIO and the haptic master/slave system was managed in real time with 1 kHz control loops. The redundancy control systems include two field-programmable gate array (FPGA) applications, which monitor and supervise the entire operation process and intervene when the system detects an emergency.
Due to CompactRIO and its flexible programming environment, the current solution is much more streamlined, reliable, and efficient than the original prototype. The new system is currently undergoing optimization, and researchers will begin preclinical tests in the near future.
This article was contributed by Mechatronics, Padova, Italy, and National Instruments, Austin, TX. For more information, Click Here