Smooth operation

Researchers have developed a robotic device that is designed to enhance the precision and reliability of minimally invasive surgery

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, where robots operate in work cells where human staff are 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.

As 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 experience with medical robotics and haptic master/slave robotic systems, Mechatronics – an Italian applied mechanics research group made up of academics and students from the universities of Padua, Udine and Trieste – 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 tumour lesion therapy called the Photon Radio-Surgery System (PRS).

The PRS is a miniaturised source of low-energy X-rays that emits radiation from the end of a probe inserted in the cranial cavity. It allows the surgeon to confine the dose of radiation to the tumour 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 3mm to 7mm in diameter. This involves considerable advantages in terms of patient trauma and post-operational recovery.
Previously, the surgeon had to manually control the PRS by positioning the device on a metal structure known as a stereotactic helmet. 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 rare spherical tumours.

Mechatronics focused on extending the PRS to patients with oblong tumour 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 tumour lesion. Due to the precision required to perform this movement, a robotic system was necessary for the application.

As a result, Mechatronics developed the Linear Actuator for Neurosurgery (LANS).

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 tumour lesion. 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. To improve the precision of the operation, a suitable virtual environment guides the surgeon during each phase of the operation.

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 lots of time to program the control and supervisory modules.

CompactRIO and modules from National Instruments were used to address these challenges. The controller was built with CompactRIO and the haptic master/slave system is managed in real time with 1kHz 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, this solution is much more streamlined, reliable, and efficient than the original prototype. The new system is undergoing optimisation, and researchers will begin preclinical tests in the near future.

What’s new
Medical devices

» clean reading
Baumer’s ED701 electrical pressure transmitter is designed for use in areas where hygiene is paramount. The measuring device features high accuracy and long-term stability. It is available with several clamp and hygienic process connections. The piezo-resistive pressure transmitter has a stainless-steel diaphragm and is based on a silicon sensor designed for high precision over a wide temperature range. If required, the zero point can be recalibrated using a mechanical adjustment. The measuring range can also be programmed, which allows for adaptation to a specific application.

» compliance guidance
Cambridge Consultants is to offer a consultancy service for medical device clinical trials. The service is aimed at saving clients time and money through a more effective method of analysing trial data. The news follows the announcement of the US Food and Drug Administration’s finalised guidance on allowing the use of Bayesian statistical analysis. The service is expected to benefit companies looking to comply with the new guidelines, but who do not have the in-house experience of designing and analysing a Bayesian trial. Support includes clinical trial planning and design, analysis of historical data, and software development.

» Encoder expansion
Faulhaber has added the PA2-50 and PA2-100 to its range of miniature optical encoders. The devices feature a custom-designed codewheel that is said to maximise the reflected light, increasing the system’s efficiency and signal reliability. Applications requiring miniature motors with precision encoders are claimed to benefit from the use of the integrated optical encoder, which is said to deliver results unattainable with magnetic encoders. PA2-xx optical technology delivers 50/100 lines per revolution before quadrature. Operating between 2.7V to 3.3V DC, low-voltage battery applications continue running for longer with higher resolution and more robust feedback signal reliability.

» Health benefit
As part of a redesign on its CT3000 non-invasive urodynamics diagnostics machine, Mediplus has included the Reomed medical isolation transformer to help the machine comply with EN 60601. At the heart of the Reomed, manufactured from UL-listed materials, is a special isolation transformer, made using a core of high-quality electrical-grade strip steel. The transformer windings use multi-layer isolation barriers and an earthed screened winding to ensure the required dielectric strength of 4kV and ’general earth leakage current’ of less than 500uA is achieved.

» Tripping the alarm
Royal Philips Electronics has introduced Lifeline with AutoAlert, a medical alert service for elderly people who have suffered a fall. It combines Philips’ Lifeline medical alert service with automatic fall-detection capabilities. Lifeline with AutoAlert is claimed to feature the only pendant-style help button that can automatically call for help if a fall is detected and a senior is unable to push the help button. According to an internal study, Lifeline with AutoAlert detected 95 per cent of many types of falls and had a low rate of false alarms.