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Imaging the Possibilities
MRI, C-arms and ultrasound continue to guide surgeons in the OR with brilliant, almost real-time pictures.
Daniel Cook
Publish Date: July 13, 2008   |  Tags:   Surgical Video and Imaging

Think about what must go through a surgeon's mind during ENT procedures. He invades and maneuvers in a tight, complex space containing the brain, carotid artery and optic nerves. How far is he from the brain stem? 4mm? Less? By referring to 3-D, almost real-time images, surgeons know exactly how close they come to critical structures — and devastating mishaps.

Providing surgeons with precise navigation as they work around delicate structures is the main motivation behind intraoperative imaging's continued development. The high-quality anatomic snapshots provided by the latest MRI, C-arm and ultrasound units also promote more precise, minimally invasive surgical techniques. Here's a quick review and preview of your current imaging options.

Imaging's Cadillac
MRI is the most current technology but also the most expensive real-time imaging option in surgery, says Wayne Coffman, RT (ARRT), MS-HAS, team and project manager for Gene Burton & Associates, a medical equipment planning firm in Franklin, Tenn. "Only a few companies offer intraoperative MRI, but they are available and they are being installed," he says, "but the cost of installation closely mirrors the cost of the equipment."

His colleague, Kelly McDonald, internal information consultant for Gene Burton, points to MRI's eye-popping price tag — as much as $8 million for a full installation — as the reason for its limited intraoperative applications. "The technology is typically used for brain surgery performed in teaching hospitals or large health systems," she says, estimating that less than 15 intraoperative MRI systems are in use throughout the country.

Two MRI options exist: fixed ceiling-mounted units or mobile magnets moved on rails built into an OR's infrastructure. After use, the mobile magnet is removed on the same rails and docked in a dedicated holding area adjacent to the OR. Those holding areas are often built between two ORs so one magnet can service two rooms.

Michael Silver, PhD, vice president of Sg2, a consulting firm in Skokie, Ill., evaluates the impact of imaging technologies on clinical care delivery. He agrees that MRI's cost constraints limit its widespread surgical application. Magnets that have not yet been designed for the OR also hamper the technology's use. "Surgical access is restricted by the magnet's shape," says Dr. Silver, adding that some manufacturers might add robotic technology to the magnet's tube — think of a da Vinci system with imaging capabilities — letting surgeons work with the magnet instead of around it. That possibility is still a ways away. For now, intraoperative MRI is reserved for large hospitals with even larger budgets.

Don't Ignore Your PACS Potential

The ultimate potential of intraoperative imaging will be limited or realized by the capabilities of your PACS (picture archiving and communication) system. "While this does not necessarily add to real-time imaging, it does provide the surgeon with immediate access to captured images," says Wayne Coffman, RT (ARRT), MS-HAS, team and project manager for Gene Burton & Associates, a medical equipment planning firm in Franklin, Tenn. "This, in combination with the modalities mentioned, would certainly provide the necessary tools for the surgeon."

David Razavi, director of media services for California Pacific Medical Center in San Francisco, oversaw the installation of the latest image-capture technology in his hospital's new state-of-the-art operating suite. He worked with physicians during the OR's design phase. They expressed a desire to call up needed images in any combination for display on the room's high-definition plasma monitors.

The surgeons at CPMC are now able to view multiple images, displayed side-by-side, for a more complete view of each individual patient. "Digital images from our radiology department, along with electronic data from PCs or medical devices, can be routed to any monitor in the new OR," says Mr. Razavi.

— Daniel Cook

Cone-beam technology
A digital, portable C-arm is a less expensive imaging modality. These units essentially give surgeons instant feedback on captured images, says Mr. Coffman. While there are many manufactures and options to choose from, he believes that the size of the imaging field-of-view and the amount of image storage space available on the unit are two of the more important considerations when evaluating a C-arm system.

"Upgrading portable C-arms is a big business and well worth the time and effort to research the many vendors," says Mr. Coffman. He advises that C-arm upgrades should include a step-up from standard analog to digital image capture, a larger imaging intensifier, upgraded software, a new X-ray tube and new mechanics (casters, cabling and knobs, for example).

Perhaps the most exciting development to C-arm imaging is the application of cone-beam imaging. Jeff Siewerdsen, PhD, senior scientist at the Ontario Cancer Institute and researcher for the University Health Network in Toronto, is active in developing that intraoperative imaging improvement.

When used on a C-arm, cone-beam imaging generates 3-D images of soft tissue, and the layers between, by taking a series of X-rays during a single rotation around the patient. The technology is made possible by upgrades to the standard C-arm design, according to Dr. Siewerdsen. Flat panel detectors provide efficient and high-quality imaging with sub-millimeter spatial resolution and little distortion. Improved X-ray tubes with an increased field of view maintain low radiation doses, about one-tenth of levels emitted by diagnostic CT, keeping staff exposure at a minimum during repeated use in the OR. Updated software systems rotate the C-arm around the patient, read the captured pictures and reconstruct them into 3-D images.

That image-capturing process differs from diagnostic CT scans, when patients are moved through an enclosed gantry while a dedicated scanner makes multiple passes around the patient in a helix-shaped path. Conventional CT produces brilliant pictures that are the backbone of diagnostic imaging, but the technology has inherent limitations in the OR, says Dr. Siewerdsen.

First and foremost, he explains, the closed geometry of the donut-shaped scanner limits surgeons' access to patients. "Never mind that moving patients during surgery presents its own set of challenges," he adds. Cone-beam imaging applied to the C-arm's open design allows high-quality imaging in a host of surgical applications, including improved navigation and confirmation during orthopedic, urologic, spine, neurological and ENT procedures.

Most ceiling-mounted C-arms are already equipped with cone-beam imaging capabilities. Incorporating the advanced imaging into mobile C-arm designs is imminent, says Dr. Siewerdsen. He believes mobile units that capture 3-D images will be the norm in the near future. He also predicts the development of multi-modal, mobile devices that can switch between 2-D fluoroscopic capture and 3-D imaging at the flip of a switch.

Dr. Siewerdsen and his researchers say the image quality achieved with early C-arm cone-beam designs isn't quite equivalent to that of a diagnostic CT scanner, but the quality is sufficient to guide surgeons to soft-tissue targets and critical structures. They warn that technical obstacles still remain before the cone-beam imaging is used routinely in the OR, but they believe it will improve surgical performance and expand the application of minimally invasive intervention techniques.

Real-time ultrasound
While ultrasound may not provide optimal resolution for surgery, it is still a very valuable tool in the OR. The latest system designs, says Dr. Silver, feature probes designed for more exact imaging, which along with a greater awareness of the technology's potential and increased surgeon training for its use, have increased ultrasound's surgical applications. The signals are more robust, he says, and developing diagnostic applications are ultimately benefiting surgical advancements.

"It's becoming more imbedded as a point-of-care device," says Dr. Silver, adding that ultrasound provides a quick-view inside the body and valuable information for immediate action. "Its users aren't looking for a high-resolution image to characterize tissue," says Dr. Silver, "they're looking to quickly identify spaces and layers between the tissue."

Ultrasound units are being designed smaller and more portable, making them better suited for use in the OR. Many systems are now as small as a laptop. One manufacturer's is even compact enough to slip into your pocket, according to Ms. McDonald. Smaller, more portable designs with improved resolution make ultrasound an increasingly cost-effective imaging option for cardiac and urologic procedures, she says. While still a developing application that's not yet standard practice, ultrasound also offers the promise of improved regional anesthesia care by letting the provider watch the placement of the needle, guiding it directly to the targeted nerve without damaging surrounding tissue or structures.

Ms. McDonald says ultrasound's 3-D images can now be seen in the fourth dimension — real time. Wayne Memorial Hospital in Honesdale, Pa., recently added 4-D ultrasound. It's used there for interventional urology, and abdominal and vascular procedures. The technology, say hospital officials, shows needle movements in three planes, increasing the accuracy of diagnostic and treatment procedures.

See better, operate better
Surgeons have long plotted invasive courses based on CT or MRI images taken days before their scalpels touch skin. Capturing 3-D images in the OR, however, resolves anatomic discrepancies that may present during surgery, anomalies that weren't captured on pre-op images. The act of cutting into and opening a patient can also cause deformities to existing structures, further jeopardizing the accuracy and ultimate usefulness of pre-op images.

"If you can see better, you can operate better," says Andrew Brill, MD, director of the newly established minimally invasive gynecologic surgery program at California Pacific Medical Center in San Francisco. "The (latest imaging) equipment allows us to see the human anatomy with a clarity and detail we've never had before. This enables us to reduce risk, to increase safety and precision, and to improve the overall quality of what we do."