Controllers: Teamwork, technology ensure successful medical machine design
The machine provides an alternative to traditional methods of mapping the heart and displaying EP catheters in real time. Getting the machine into human clinical trials fast depended on choosing capable partners, and selecting a control platform with easily implemented hot back up capability.
Manually navigating the twists and turns of an artery, and performing a therapeutic procedure within a human heart, demand high degrees of surgical training, practice and manual dexterity. A wrong move could tear a blood vessel or puncture a heart wall. Aerospace and defense technology pioneer Josh Shachar knew there had to be a better way to move an electrophysiology (EP) catheter than by hand. He envisioned a system that would use electromagnetic fields, instead of manual prodding, to help a physician guide the catheter in a safe and effective procedure.
Shachar is the founder and president of Inglewood, Calif.-based Magnetecs , maker of the Magnetecs Catheter Guidance Control and Imaging System (CGCI). He knew that electromagnetism could guide a catheter based on his experience with electromagnets used in other highly-advanced fields. "At the core of any engineering task is the fundamental and unassailable belief that a solution is possible," he says. What comes next is a combination of vision, teamwork and technology that can implement the solution and, in this case, get a new medical machine into human clinical trials fast. So many parts need to come together, and all contribute to success. A control platform with easily implemented hot back up capability was one of the keys.
"The speed at getting CGCI to human clinical trials would not have been possible if Magnetecs chose a different platform," says RK Controls general manager Robert Karkafi. "I have seen companies using other platforms where they have spent months and months writing code to make sure the hot back up is operating correctly." Magnetecs' choice, however, came preprogrammed as a standalone unit.
Physicians rely on cardiac ablation to treat arrhythmia — an abnormal heartbeatst effective treatment is to destroy the tissue at the location of the short circuit using the EP catheter for cardiac ablation.
Beginning in 1997, Shachar, later joined by Magnetecs Chief Scientist Laszlo Farkas and VP Engineering Leslie Farkas, produced several promising, small-scale prototypes. They encountered several naysayers from major international companies who said the technology was not available to generate and control magnetic fields, but they persevered in engineering and design work. Today, the CGCI system they developed is entering the human testing stage.
Vision becomes reality
CGCI is the world's first system to employ magnetic waveguide forming technology that focuses magnetic waves -- like light through a lens - to generate a magnetic lobe (about the size of a basketball) around the tip of the catheter. The magnetic lobe is formed by eight electromagnets that surround the patient's torso. A real-time, computerized controller calculates the current values for each electromagnet. The signal from the controller is amplified by eight, high-efficiency amplifiers.
By altering the polarity and current of each coil with a tactile joystick, a surgeon can reshape the magnetic lobe in milliseconds. As a result, the doctor enjoys five degrees of freedom in 3D space to move the flexible, magnetic tip in synchronization with a beating heart, without ever generating enough force on the tip to damage or puncture a blood vessel or heart tissue. CGCI allows the doctor to manually or automatically guide the catheter to locations in the heart mapped by the St Jude Medical EnSite mapping system. The joystick is used for manual control. A mouse may be used to point-and-click on a selected location, and the CGCI will automatically guide the catheter to that location.
CGCI is capable of using torque to twist the magnetic catheter tip in a particular direction, and also is capable of using force to translate the magnetic catheter tip in any direction without rotating it. This is the five-degree of freedom control. Up to 35 grams of force is available for contact pressure, but the doctor may select less as the situation requires.
CGCI is also opening doors for not-too-far-off advancements in cardiovascular, gastrointestinal, neurological and gynecological therapeutics. For example, it can control un-tethered cameras and probes within the body.
Together with industrial automation distributor RK Controls, electrical controls engeineer Mason Mattenson worked non-stop putting the control system together. The complexity of the project was compounded by the addition of new modules or pieces of equipment to the system.
Selecting the right controller platform
Magnetecs chose a programmable logic control (PLC) system from Siemens to provide automated and redundant safety monitoring and smooth startup and shutdown of the CGCI system. The Simatic S7-400H redundant controller system, programmed with Step 7 software, ensures that CGCI performs safely and with high availability. "We originally used our own software to control all aspects of turning the system on and off," said Leslie Farkas. "Additionally, our systems were initially responsible for validation of the hardware and its reliability, but there was no redundancy."
Farkas, who has a scientific background researching magnetic fields and guiding particles, including work at the Fermi National Accelerator Lab, was familiar with the redundant capabilities of the S7 400H controller. "Siemens products are available off the shelf anywhere in world. The technology is tried and true and will help us get the necessary clearances. Siemens support is also available around the globe," she said.
In January 2009, Magnetecs hired automation and controls expert Mason Mattenson to design, install and program the redundant control system. Mattenson, an electrical controls engineer, had previously developed automation platforms for everything from high speed amusement rides to national defense systems. He was given just four months, until May 2009, to complete the project. This was also his first experience with a Siemens platform; he had previously worked for 18 years on Allen-Bradley systems.
"My challenge was making sure that the S7 400H fit our needs. I checked every module, I/O and device that was installed in this system to ensure successful interface with the Siemens platform," said Mattenson.
Together with nearby Siemens high-tech industrial automation distributor RK Controls , Mattenson worked non-stop putting the control system together. The complexity of the project was compounded by the constant addition of new modules or pieces of equipment to the system. He had little time for problems with control equipment orders.
Support from distributor and vendor
"I was impressed not only with the equipment, but with the help offered by RK Controls," Mattenson recalled. "The I/O list changed frequently in development, and each delivery was well planned and organized. All of the documentation came with the proper components. Florence Sleiman of RK Controls was always here to make sure we received everything we ordered. Great service kept logistical issues at a minimum, so I could focus on the technical aspects of the project."
Mattenson also attended the Siemens "AB to Step-7" course offered locally at the Siemens office in Cypress, Calif. The class, which focuses on transitioning from Allen-Bradley to Siemens technology, helped speed the learning process. The telephone support he received also was a pleasant surprise, he said.
Within a very short time after joining Magnetecs, Mattenson had the entire system configured in his office. He was quickly demonstrating communication with all of the input and output modules and the redundancy of the system. On Sunday, May 10, one day before the deadline, the CGCI system was operational. "In the end, Mason and I wired up the system, turned it on, and there was not one wire out of place," Farkas said.
The S7 400H controllers have preprogrammed failover routines developed by Siemens as a standalone redundant CPU system. That meant Mattenson did not have to worry about any of the background code that moves information from the active controller to the standby unit. Communicating via Profibus over fiber optics, the active S7 400H controller monitors and controls the critical system parameters and functions of the CGCI, including system startup and shutdown, system fault monitoring and emergency stop. The controller also monitors amplifier command current vs. actual coil current as well as coil cooling and temperatures, flow and alarms.
How redundancy works
If an amplifier module faulted, for example, the controller would automatically determine the cause of the problem. If the fault did not affect any part of the clinical procedure, the PLC controller would not initially send an alarm to the physician's central monitor, but would internally log the event on a human machine interface (HMI) programmed with Siemens WinCC SCADA software located in the equipment room. If the controller could not reset the fault, it would start a warning procedure.
However, if the fault causes a change to the clinical procedure - such as when a coil or a combination of coils develops a heating problem — the controller would correct it or go into a lower power state and alert the EP physician. The physician can then decide whether to proceed with the procedure. If the temperature continues to climb and the coil is overheating, the controller will tell the physician it is using lower power and, again, the physician decides on the next steps.
"The controller is out of the decision making loop for patient safety," Farkas says. "It keeps the system from hurting the patient and itself. It is a watchdog and reduces the chances for error."
The data logging and remote communications capabilities of the WinCC HMI will also help hospitals lower maintenance costs, Farkas said, by reducing the need for representatives and technicians to troubleshoot the system. If an event occurs, the WinCC HMI records the occurrence and provides additional data on the cause of the problem.
"We have the forensic capability to make very quick decisions," Farkas said. "We can log on to any installation, anywhere in the world, and see the trend. In fact, our computers will be programmed to monitor every unit. We can contact a hospital even before its staff knows there is a problem."
On the clinical side
The computer-based CGCI system creates three-dimensional graphical displays of cardiac structures and arrhythmias, providing the EP physician with precise targets for cardiac ablation.
On the clinical side, the CGCI provides an alternative to traditional, non-stop fluoroscopy with St. Jude Medical's EnSite System that maps the heart and displays EP catheters in real time. The computer-based system creates three-dimensional graphical displays of cardiac structures and arrhythmias, providing the EP physician with precise targets for cardiac ablation. The CGCI system unifies the EnSite NavX mapping system and the display of other operating room equipment. The CGCI uses EnSite catheter position information to guide the catheters to locations that are specified in a common coordinate system between EnSite and CGCI.
The intuitive and easy to operate system takes only days at most to master, eliminating the need for extensive training and practice. CGCI is operated from the control room or the operating room. Remote web-based interfaces are not yet available or approved by the U.S. or European regulatory authorities, but are likely to become a reality, allowing robotic surgery to be performed from next door or half way around the world.
As it comes into contact with tissue, pressure on the end of the catheter is simultaneously felt by the doctor through the joystick. As the catheter is maneuvered in a heart atrium or ventricle, the CGCI Software, EnSite mapping system and catheter tip work together to map and identify the areas to be ablated. The doctor guides the tip of the catheter to the points for treatment, either manually using the joystick or automatically using a mouse click on the spot to be ablated. The ablations are performed by the doctor using a foot-pedal to activate the ablation generator. At any point in the procedure, the surgeon can automatically and safely extract the patient from the CGCI apparatus within five seconds.
In a typical cardiac ablation procedure today, the physician is positioned next to the patient, and fluoroscopic radiation continually affects the patient, doctor and support staff throughout the operating room. The CGCI system, combined with the EnSite mapping system, can greatly reduce the need for fluoroscopy, and the EP physician and staff can be entirely shielded from radiation while performing the procedure from the control room.
While the eight, shielded electromagnets generate up to 1400 Gauss inside the magnetic lobe, only 5 Gauss is detectable two feet from the outer surface of the CGCI magnetic array. Doctors and technicians can work in close proximity to the CGCI without fearing that the powerful electromagnets will affect the functioning of operating room equipment, wipe away credit card information, ruin wrist watches or disrupt pacemakers.
Today, the vision of Magnetecs' founder Shachar is coming to fruition. The CGCI system is expected to change the way EP procedures are performed on a global scale. The devoted engineering teams from Magnetecs, Siemens and RK Controls have taken the concept of the CGCI's waveguide forming technology from "it cannot be done" to human testing by some of world's most prestigious medical centers. Thanks to these partnerships, safer and easier procedures will soon be available to almost all who need them.
- Edited by Renee Robbins, senior editor
Control Engineering News Desk