Images Guide Surgery

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Doing more, with less - isn't that what we hear about all the time in healthcare? Well, what about doing more, with more. That is what image-guided surgery technology is allowing surgeons to do. The powerful navigation systems and tools are expanding the possibility of preoperative and intraoperative image guidance, all of which are performed less invasively. And it's not just cranial surgery for which IGS is standard of care, applications in ENT surgery are maturing and orthopedic trauma and spinal surgeons are adopting the technology as well.

Image-guided surgery (IGS) enables surgeons to perform complex, minimally invasive surgery (MIS). IGS technology combines high-speed computers, specialized software and tracking techniques so that surgeons can view three dimensional (3D) images of body organs and their relation to surgical instruments. Precision increases twofold and surgeons can more accurately and safely access anatomy through natural body openings or smaller surgical incisions so that patients experience less trauma, shorter hospital stays and reduced pain.

Prior to IGS, a surgeons' field of view was limited to the end of an endoscope when performing MIS. A bit of estimation was needed to correlate the patient's preoperative medical images with the operative field. Image-guidance technology, on the other hand, automatically correlates a patient's electronic images with the movements of surgical instruments and displays this on a monitor in the operating room.

For preoperative image guidance, a patient typically undergoes a CT or MR scan prior to surgery. The images, used by the surgeons to map out their surgical pathways, also are imported into the IGS software right before surgery to register the patient's physical anatomy to the computer scan information. Surgeons can then track in real-time their progress on the IGS monitor.

Neurosurgeons use image guidance to locate intracranial lesions for resection or biopsy. "The benefits are that you can plan the craniotomy with a knowledge of exactly what you are going to see beneath the surface," says Alexandra Golby, MD,
associate surgeon, Brigham & Women's Hospital, Neurosurgery Department, and instructor at Harvard Medical School. "This allows us to make smaller craniotomies, more precise craniotomies, it allows us to attack the tumor more directly and have the patients leave the hospital faster with less recovery time."

The 10-year-old technology has come a long way. "[IGS] used to be a whole different ballgame," says Golby. "It used to be line-of-sight dependent and the receiver used to be on a separate boom in the room. Now we have the ability to co-register various scans, we can fuse CTs to MRIs, we can incorporate functional data, we can use the system to place stunts and place biopsies."


PUSHING THE ENVELOPE

Neurosurgeons need to know at the time of surgery precisely the intricate details of brain anatomy and function as well as the relation of the surgical site to normal structures. Multimodality images such as CT, MRI, SPECT and PET - along with budding technologies such as spectroscopy, diffusion tensor imaging and functional MRI - help neurosurgeons better identify this information. Image guidance will allow surgeons to bring this rich data into the OR and navigate with it, says Warren Boling, MD, assistant professor of neurosurgery at West Virginia University Medical Center (WVU).

Applying the science of imaging to the art of surgery is part of a collaboration WVU has with IGS vendor BrainLAB Inc. of Munich, Germany. Researchers at WVU's Center for Advanced Imaging use BrainLAB's VectorVision IGS technology to improve the process of identifying subtle lesions on the brain and navigating around the brain in an effort to make neurosurgery safer, says Boling. WVU researchers want to develop new IGS applications such as tracing the fiber tracks of the brain, integrating functional MRI into image guidance and integrating an ultrasound device into image guidance.

The backbone to this is WVU's substantial investment in a robust IT infrastructure for the hospital's new surgical suite. By integrating BrainLAB with radiology's PACS, electronic medical images will literally be at the fingertips of surgeons prior to and during surgery. "Our goal is to directly bring imaging into the OR and have the ability to upload electronic medical images [from the hospital's filmless radiology department] into image guidance directly through a wire," forsees Boling. "Right now the process is cumbersome and some images may need to be put on a CD-ROM or zip disk to transport them around the hospital. The goal is for all that to be seamless and completely integrated."


REAL-TIME VISUALIZATION

Preoperative images are limiting once intracranial contents move during surgery. It was only a matter of time once surgical navigation took flight that neurosurgeons would begin to exploring the possibility of imaging during surgery, a.k.a. intraoperative image guidance.

"Intraoperative became the new movement in image guidance with real-time imaging, particularly in the nineties with the introduction of intraoperative MRI, CT and sonography," says George Bovis, MD, a staff neurosurgeon at Advocate Lutheran General Hospital in Park Ridge, Ill. With intraoperative images, neurosurgeons confirm their optimal surgical approach during surgery and verify complete tumor removal prior to closure.

Neurosurgeons at Advocate use the PoleStar N-20 iMR guidance system (distributed by Medtronic Surgical Navigation Technologies) for patients with brain tumors, metastatic tumors and pituitary tumors. "The system allows surgeons to easily obtain images intraoperatively and track their real-time resection," says Bovis. "Patients are brought into the room and we obtain an MRI scan with the patient on the table, which are used for preoperative study. We perform our craniotomy, remove the tumor as completely as we find appropriate, and then we obtain an image while the patient is asleep by elevating the two magnets of the gantry. With the updated images, we may re-navigate the stereotactic instruments to guide the rest of our surgery."

Designed for use in a conventional OR, the PoleStar is a low-field (0.15 Tesla) mobile unit small enough to be stored underneath an operating table. "We are limited when we have a 900-pound device as well as where we can position a patient at times," says Bovis. "But its open gantry design, vertical magnet and remote control maneuverability allows us better ease of positioning, easier scanning and better surgical comfort."

A drawback however is extra time required in the OR. "The operating times are an extra 45 to 90 minutes longer than a typical operation," explains Bovis. Another challenge is cost. "An intraoperative device can cost between $1 million to $3 million depending on retrofitting the room and other devices that need to be purchased such as titanium and ceramic equipment that will not distort image quality," contends Bovis. "At the same time, it is seen as the latest generation of image guidance. When it gets out in the public that one hospital has this device, the volume that one does with the system is higher."  


EXPANDING BREADTH

Interactive IGS navigation is by no means limited to neurosurgery. ENT (ear, nose and throat) applications are maturing and surgeons use IGS in this segment to perform more minimally invasive procedures. Rick Chandra, MD, director of the Division of Nasal and Sinus Disorders at the University of Tennessee (UT), uses GE's InstaTrak ENT on 50 percent of sinus-related cases at Methodist University Hospital (Memphis, Tenn.), affiliated with UT.

The 3D dataset enables Chandra to avoid critical structures, such as the optic nerve and brain, while closing CSF (cerebrospinal fluid) leaks, removing sinus or skull base tumors and performing revision of endoscopic sinus surgery. "It broadens the horizon for endoscopic sinus surgery and minimally invasive management of complicated conditions," says Chandra.

"The surgical procedure depending on what you are doing may be longer or shorter, because today, minimally invasive procedures may take more time since these approaches often require more meticulous techniques," adds Chandra. However, recovery time, hospital stay, and risk of scarring significantly improve.

"There are two monitors in the room," explains Chandra. "One with the endoscopic monitor that shows the anatomy that is being operated on. The image guidance monitor shows where your probe is in relation to the CT scan. We teach residents that the frame of reference is not the CT monitor, it's the endoscopic monitor. But when you see a structure and you want to confirm what it is, you put your probe on that structure and refer to the image guidance monitor."

Considered state of the art, IGS is a flourishing technology that is a boon for business, especially when applied to niche applications. Its clinical advantages can help offset the cost of the technology, which depending on configuration, can range anywhere from $120,000 to $400,000. Return on investment is better justified by the potential for increased accuracy, greater patient-turnover, faster recovery, and shorter hospital stay.   


IN THE HEAT OF BATTLE

Expanding applications helped the IGS market garner $144.6 million in 2003, according to Frost & Sullivan. Continuous upgrades to surgical navigation systems and tools - in addition to new options and functionalities - have helped applications such as orthopedics and spinal gain a foothold in IGS.

Additional utilities have been needed for orthopedic trauma surgery and only recently have companies began serving up systems with these powers. The trauma team at University of Virginia Health System (UVA) has been using BrainLAB's VectorVision trauma system since December.

"In OR, we do a lot of image-guided procedures using fluoroscopy," says David Kahler, MD, director of Orthopedic Trauma and associate professor of Orthopedic Surgery at UVA. "Pretty much every orthopedic trauma surgeon is proficient in this technique for pinning a hip or placing a femoral nail. But we do it at the expense of a relatively large amount of fluoroscopy time and radiation exposure to both ourselves and the patient."

In order for a surgeon to be able to verify the bony anatomy and the position of his instruments, an x-ray device constantly emits x-rays in order to provide the most up-to-date images. In the heat of battle, Kahler says it happens that surgeons put their hands right in the C-arm beam when trying to do a difficult part of the procedure. With image guidance, only few images are taken of the patient's anatomy prior to surgery and downloaded in the VectorVision system. With the images and trauma software, surgeons can navigate instruments such as screws and drills in real time, virtually reducing the fracture.

The system is very well suited for routine trauma procedures, such as pinning a hip fracture or locking a femoral nail, notes Kahler, and he also uses the system to perform pelvic and acetabular fracture work less invasively, which are typically open, bloody procedures.

"It's an enabling tool for smaller incisions," explains Kahler. "In the case of certain acetabular fractures now, we can fix these with just two of three small stab incisions. We generally insert pins in the bones to act as joysticks to allow us to reduce the fracture and then use the image guidance to pass two or three screws across the fracture line to stabalize the fracture. For people with isolated acetabular fractures, we can usually get the length of stay down to less than two days, where a week was routine for these procedures."





Harvesting the Power of 3D

To perform intraoperative 3D image guidance during spinal surgeries, physicians at Emory University Hospital use Siemens' SIREMOBIL Iso-C3D system.

The imaging device, priced at $200,000, takes a series of 2D images while the C-arm rotates 190 degrees around the anatomy. In a little over two minutes, 3D datasets are generated and immediately available on the C-arm monitor. The data are available for real-time tracking of implants and screws and imported into Medtronics' StealthStation.

"The Iso-C is a new technology that weds nicely with something that has already been well established - computer assisted 3D guided surgery - but it gives us an instant dataset right there in the operating room," says Gerald Rodts, MD, professor of neurosurgery at Emory University Hospital and director of the hospital's neurosurgery spine program. "Most predominantly, the system is being used to place screws in areas where there is high risk to the spinal cord or injury to arteries. Sometimes we have to place screws with no more room than one millimeter."

The images are not as powerful as a pre-op CT scans, but their quality is very satisfactory for cervical, thoracic and lumbar spine surgery, notes Rodts. It also combats the problem of obsolete pre-op CT scans that surgeons can not use once a patient's anatomy changes during surgery.

In the future, Rodts says the technology is helping merge minimally invasive surgery and biologics. "With some of these minimally invasive operations, we can also minimize pain and trauma by not taking extensive bone grafts and just placing BMP (bone morphogenetic protein) where we want bone to heal," explains Rodts. "This has been a huge development in spine surgery."