Image-guided surgery (IGS) has evolved from posting pre-operative diagnostic X-rays on a light box in the operating room, into complex systems capable of directing the surgeon’s hands during interventional procedures. Today, three primary driving forces propel image-guided surgery with developing technologies. Navigational systems give surgeons information about the placement of their instruments in relation to preoperative images, intraoperative MRI and ultrasound imaging techniques and a massive research program at The Brigham and Women’s Hospital (Boston) in the Surgical Planning Laboratory to develop real-time 3D images intraoperatively, are three directions of these important activities.
BrainLAB, AG (Munich, Germany) provides worldwide distribution of image-guided surgery and stereotactic radiosurgery systems. VectorVision, considered a “global positioning system for the body” enables neurosurgeons and other specialists to correlate the position of their instruments relative to preoperative diagnostic images from computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET) and assorted data. Originally developed for cranial work, this system is now being used by orthopedists and ENT (ear, nose and throat) specialists.
Eric Lindquist, BrainLAB’s executive vice president of marketing, explains that for an image-guided surgery system to function effectively, rigid anatomy such as bone serves as a reference point. This FDA-cleared system features a powerful computer system, touchscreen monitor and two cameras that emit infrared signals capable of determining the patient’s position on the operating room table as well as the location of individual surgical instruments in relation to the patient’s head.
BrainLAB’s intuitive software permits navigation using virtually any pre-existing surgical instrument so that a surgery department would not be required to purchase special surgical instruments in order to use this image-guidance system. Once one of BrainLAB’s lightweight universal instrument adaptor clamps is attached to an instrument, a one-time three-second calibration is accomplished and the selected instrument is ready for use with the system.
Although this system was used originally for neurosurgical procedures, it is now expanding beyond those bounds into sinus surgery and knee replacements.
Jay Klarsfeld, M.D., president of Advanced Specialty Care in Danbury, Conn., uses the BrainLAB VectorVision system for functional endoscopic sinus surgery.
“This allows me to do procedures transnasally that previously I had to do with an incision over the top of the head,” explains Klarsfeld. “It allows me to reach a sinus safely through the nose.” With little margin for error given that sinuses are in close proximity to the cranial cavity, image guidance gains additional importance.
Using preoperative images from CT that are loaded into the unit, the system is capable of correlating those views to the live patient on the OR table. A laser determines the contours of the face and matches the data entered into the IGS unit, the system is activated, and images appear on the monitor screen. Klarsfeld appreciates the fact that prior to surgery he does not require a second CT scan, because all of the primary clinicians order the original diagnostic scan using the BrainLAB protocol.
Orthopedist Michael L. Swank, M.D., medical director of the joint replacement center, Freiburg Orthopedics and Sports Medicine, Jewish Hospital in Cincinnati, is equally enthusiastic about the use of this system for total knee replacement.
In this type of surgery, the patient’s leg is prepped and draped before the incision is made. Therefore, the surgeon is unable to see the operative site in relation to other portions of the leg, either above or below the knee. In arthritic patients, often deformities are caused by the disease, or some patients have an unrelated former fracture that changes the alignment of the long bones on either side of the knee. The orthopedic surgeon makes cuts in the bone to place a prosthetic device, and the angle of the cut is enormously important to future function of the prosthesis.
“To make their limb straight, we have to cut the bone at an angle to the way the bone normally runs,” Swank explains. “This angle is not a straight end on cut. The CT scan allows us to represent where that angle actually is, so when we make our cuts on the real bone, we know we’re making it at the angle we want, and that it represents the person’s real anatomy.”
Accurate prosthetic placement is important to outcome both for function of the patient’s knee, and for the longevity of the prosthetic device.
“Instead of guessing and being within three or four degrees, which is what our instrumentation systems allow, theoretically we should be within a degree or half a degree,” concludes Swank. The BrainLAB system has enabled this level of precision. Previous studies on malalignments revealed that if a knee is “off” by more than three or four degrees, there are many long-term issues related to loosening of the components and polyethylene wear of the knee replacement prosthetic. On the human side, Swank notes that a patient with appropriate leg alignment feels better.
The StealthStation from Medtronic Surgical Navigation Technologies (Louisville, Colo.) is another image-guided surgery platform that is being used in a variety of surgical settings for many different types of clinical procedures. Invented 10 years ago, its original purpose was to guide surgical instruments for cranial neurosurgery using preoperative CT or MRI images of the brain correlated to the patient and surgical instruments in the OR. Its utility has been expanded into orthopedic, spinal, and ENT surgical procedures. Eventually, the company anticipates the system will be used for vascular interventional and cardiac procedures, or in soft tissue applications.
Currently the system uses an optical system to “view” instruments in relationship to the patient’s body, and superimpose that information on preoperative images.
“We essentially put a camera in the room, an optical system,” explains Andrew M. Weiss, vice president and general manager of Medtronic Surgical Navigation Technologies. “It either emits light or looks for reflected light, at a very specific wavelength. Then on the instruments we attach little LEDs that give off this light or reflecting balls that reflect back light.” The camera must physically “see” these lights on either the patient or the system in order for it to work. However, given a surgical environment, drapes or the surgeon’s head can get in the way.
For this reason, Medtronic has invested between $10 million and $20 million towards a new technology called electromagnetic localization. This system will establish a specific magnetic field in the patient’s body. Once small coils of wire are attached to surgical instruments, those coils will be located by the system in the magnetic field. This approach will allow coils to be placed on the tip of a flexible catheter, or a guiding stylette or probe. They will be able to locate multiple devices like this inside the patient’s body which should facilitate minimal access procedures. Weiss says they hope to launch this technology within a year.
Richard D. Bucholz, M.D., F.A.C.S., the Smith Endowed Professor of Neurosurgery and director of the Jean H. Bakewell Section of Image Guided Surgery at St. Louis University in Missouri, was a co-developer of the StealthStation system. He describes that it was used first for cranial surgery in 1991 on a prototype he built, but has now moved to many other applications.
“I see the StealthStation and its technology more as a portal than as a final device,” says Bucholz. He believes that eventually not only medical images, but also data from brain stimulations, brain recordings, and other neurophysiology information will be incorporated into the system output.
“Just like imaging, the results of neurophysiology can be arranged and organized in a 3D anatomical world,” explains Bucholz. He anticipates a field expansion that moves from image-guided surgery to an era of information guided therapy where data from diverse sources, not only what is considered classic images in such as MRI and CT, as well as information from PET scanning, other functional studies, neurophysiology, chemical analysis and other studies will inform treatment decisions.
Intraoperative MRI
In the past, routine neurosurgery involved preoperative MRI imaging, and then post-operative studies to see what had been accomplished. Some of today’s operating rooms feature MRI scanners that are capable of performing studies during the procedure to direct neurosurgeons, especially in tumor resections.
Siemens Medical Solutions (Iselin, N.J.) offers the Magnetom Concerto as a 0.2 Tesla open MRI system where the operative bed slides into the magnet.
“When you open the brain, it is a very soft tissue,” explains Michael Wendt, Siemens manager of MR research and development. Once any part of the tumor is removed, the rest of the brain shifts in position, so the situation is different than preoperative images would suggest. To have an MRI image at the midpoint of an operation means the neurosurgeon would know how much of the tumor is left to be resected, and avoid removing tissue that should remain in place.
The University of California at Los Angeles has recently installed a higher field Siemens 1.5 Tesla Open MR in the operating room, where the table swivels in and out of the scanner to permit as many intraoperative imaging sessions as necessary.
“We get a beautiful picture that increases the safety of many procedures and the likelihood of a successful outcome,” says Donald Becker, M.D., director of UCLAs Brain Tumor and Interventional MR program.
According to Becker, obtaining MR images in the operating room helps to reduce the need for follow-up procedures because any new blood clot, brain edema and other complications are readily detectable and can be addressed before the patient is awakened. In addition, the MR scans enable surgeons to concentrate specifically on the area of interest, while making smaller incisions and reducing the risks inherent in surgery.
Prior to development of this intraoperative imaging capability, neurosurgeons might not excise the entire tumor, and not be aware of that result until the post operative MR scan was performed the next day.
Odin Medical Technologies Inc. (Newton, Mass.) offers PoleStar, the first intraoperative MR imaging system that is designed for installation in a conventional operating room. The magnetic field is confined to the area between the magnet poles and its immediate proximity. This unit is wheeled to the operating table, and occupies space under the table when not in use. When a scan is required, the system is elevated to scanning position by pushing a single button.
The beauty of this FDA-cleared compact MRI system is that it enables real-time visualization during all stages of a cranial procedure. Especially beneficial to tumor resection, it provides accurate representation of tumor margins to permit complete resection without removing healthy brain tissue. The verification of lesion removal prior to closing the cranium has been shown to increase patient survival rates.
Michael Schulder, M.D., associate professor of neurosurgery and director of image guided neurosurgery at New Jersey Medical School in Newark, has been using the PoleStar since it was installed at this first U.S. site.
“I’ve come to use it as the standard tool for stereotactic navigation in the OR with the added advantage of intraoperative updated images at any point in the procedure,” says Schulder. They have found reduction in their surgical procedure times as shorter imaging sequences that offer the opportunity to use the system for stereotactic targeting.
They use gadolinium contrast injections when necessary. Schulder explains that contrast enhancement usually lasts for about an hour, and they will re-inject if necessary. In patients with normal renal and liver function, additional doses do not cause problems, but Schulder says he has never done more than three contrast injections in a given surgery.
It is important that the large anesthesia equipment be MRI-compatible so that the images do not exhibit interference patterns, but other large capital tools, such as the operating microscope, ultrasonic aspirator and power drills are all standard equipment. This equipment is not attracted strongly enough when the magnet is below the operating table. Staff turns off the lights and electrical equipment as an image is acquired, but that takes a minute or less.
Although their operating room has been specially shielded to avoid radiofrequency interference to maintain image quality, they are testing a new accordion-like device that serves as a local shield over the patient and table, and that will obviate the need for shielding the entire room.
Tumor ablation and ultrasound guidance
Some liver tumors are considered inoperable due to their location, or the patient’s condition. Radiofrequency ablation (RFA) has become a treatment option for patients who are ineligible for surgical resection.
RITA Medical Systems Inc. (Mountain View, Calif.) has developed a minimally invasive RFA system which has proven effective in treating a variety of malignant and benign tumors.
“We have a needle electrode which we insert directly into a tumor under image guidance, and heat it to a temperature high enough to kill the tumor,” explains RITA’s president and CEO, Barry Cheskin. “We achieve a strong clinical result, with a recurrence rate at one year of approximately 15 percent, about the same as surgery.”
This system features temperature monitoring in a carefully designed configuration, with a curved wire array. The system can destroy a tumor about the size of a tennis ball while sparing normal tissue.
Joseph Espat, M.D., director of hepatic regional therapies at the University of Illinois at Chicago, has found the RITA 7-0 RFA system to be quite effective.
“The biggest reason we’re limited in our resection of liver tumors is if there is proximity to the portal or hepatic vein,” says Espat. Using RFA, and a B&K Ultrasound with targeting system, he has been able to treat patients who were not candidates for surgical intervention.
Research for the future
The Brigham and Women’s Hospital is home to 120 researchers who work in different aspects of image-guided surgery and develop new techniques in intraoperative imaging. Ron Kikinis, M.D., serves as director of the Surgical Planning laboratory with 25 computer scientists who provide the IT infrastructure to the entire image-guided therapy program.
“My laboratory takes imaging data and processes it to generate 3D models and other types of renditions to be used during surgical interventions,” says Kikinis. The lab uses the GE Medical Systems (Waukesha, Wis.) Signa 0.5 Tesla MRI system for intraoperative imaging in neurosurgical procedures.
Ten years ago, it would take a week to process an image into a 3D rendering. Now, using an extremely powerful computer, the Sunfire 6800 from Sun Microsystems Inc. (Palo Alto, Calif.), they have been able to reduce processing time to a few minutes, making it very attractive for intraoperative use.
“It allows the surgeons, on many occasions for tumor resections, to be more aggressive because they know how much further they have to go,” says Kikinis.
Bjorn Anderson, group marketing manager volume system group at Sun Microsystems, describes the benefits of using their processors and workstations that are capable of producing image resolution of 1280 by 1024 pixels on a workstation screen. The speed of processing is a major benefit to this type of work.
Anderson stresses that quality in a system includes maintaining a 24×7 uptime requirement in the workstation and graphics package.
“During brain surgery, you don’t want to have a system crash,” says Anderson. “We don’t get viruses. Sun Systems are designed to stay up, mission critical quality as we have developed in our data centers.”
As image-guided surgical procedures continue in development, new techniques are devised to improve surgical outcome. Imaging technology plays a primary role in all phases: preoperative, post operative and intraoperative.
