Futuristic technology like image guided surgery (IGS) may sound like something out of a science fiction novel, but it's becoming an increasingly popular way to do ENT, neurological, and orthopedic cases. IGS helps surgeons perform surgery safer by providing them with digital interactive images of the surgical site. Because image guidance provides greater precision and promotes less invasive surgery, patients in turn benefit. I have been working with image guidance for several years now; in fact, we just purchased a new system a year and a half ago. In this article, I hope to help you decide if this technology might be a good investment for your facility.

The technology
Image guided surgery, also called computer-aided surgery, is a technology that uses pre-operative data from MRI, CT, or PET scans to guide surgical procedures. The system uses the images to render an interactive display of the surgical site. It's like a global positioning satellite system for the head.

Some proponents of image guided surgery suggest that it allows for smaller incisions. While these claims may be true for some specialties, I have not found this to be the case. But I still have found its benefits to be indispensable. Because sinus anatomy can be very difficult to visualize, the image guidance system provides me with the extra information I need to have complete confidence during the operation. I've even had occasions during revision sinus surgery where the anatomy was distorted enough that I was really surprised by what the system was telling me. It didn't match what I was envisioning in my mind, but the system was completely accurate. Using image guidance helps me do more complete surgery and do it a lot safer. I can now go to the limits of the sinuses to remove polyps or clear blocked sinuses and be confident of where I am. In our outpatient facility, about 90 percent of our image guidance cases are sinus procedures, and we are doing about 15 of them a month.

How the system works
We usually do a CT scan at the patient's pre-operative visit a couple of days before the procedure, but it can be done anytime up to a month before. We use an axial CT that is soft tissue windowed, meaning that the soft tissue, such as skin, fat, and muscle, are more visible than the bone. In most cases, you can use PET, CT, or MRI images.

Our CT scanner is on a network here at our hospital, and the images are sent from radiology to my computer in my office. This computer, which we call a transfer station, is a high-speed PC that formats the CT images into a format that the image guided surgery system can read. I then download that information onto a zip disk, which I take with me into the OR.

The actual image guided surgery system consists of four parts:

1) A hand-held laser pointer, which we use to scan the surface of the patient's face.

2) Adapter clamps, which attach to our standard instruments (unlike some other systems, we did not have to buy new instruments to use with this system). The clamps, which stay on the instruments throughout the procedure, feature passive markers that reflect infrared light.

3) A headband, which the patient wears across his forehead. The headband is also fitted with three passive infrared markers.

4) The main unit, which features an infrared camera. This camera sends out beams of infrared light, which are reflected back by the passive markers. The main unit also has a video monitor.

In the OR, I first download the CT scans into the unit from the zip disk. The images are displayed on the monitor as sagittal, coronal, and axial, views. While I am doing this, the anesthesiologist administers the anesthesia. The system then prompts me to "register" the patient, which means make a digital map of the patient's face using the system's laser registration. To do this, I scan the surface of the patient's face with the hand-held laser, and the system's surface-matching algorithm calculates and displays the contours of the patient's face on the monitor (this takes about 45 seconds). The registration correlates the position of the patient's head in real-time with the CT scans.

Choosing a system When Dr. Senior's facility decided to purchase an image guided system, their first step was to call around to vendors. Dr. Senior contacted all major companies involved with image guidance, spoke to their sales representatives, and arranged to have them demo their systems in his facility. He also did a set number of cases with each one of the competing systems. "I found the technology to be fairly similar in terms of the overall quality of images. When I was evaluating the different systems, usability was the most critical factor," he says. He suggests looking for the system that is most intuitive to you. Implementing the image guidance system at Dr. Senior's facility cost us about $250,000. But the prices vary dramatically from vendor to vendor. Dr. Senior also recommends asking your sales rep if the CT scanner you are currently using is compatible with whatever system you decide to purchase. "I was talking to a doctor recently who said the old CT scanner that he owned, which gives him reasonable quality images to do surgery from, was apparently not applicable for his system," he says. Here are some manufacturers who offer image guidance technology. Aesculap www.aesculap.de 0049-7461-95-0 CBYON www.cbyon.com (877) 819-1900 Compass International www.compass.com (507) 281-2143 GE Medical Systems, Inc. www.gemedical systems.com (800) 558-5102 Leica www.leica-microsystems.com (800) 526-0355 Marconi www.marconi.com 44-011-20-7493-8484 Medtronic Surgical Navigation Technologies www.stealthnavigator.com (720) 890-3200 Ohio Medical www.ohiomed.com (800) 755-6381 Philips Medical Systems www.medical.philips.com (800) 526-4963 Radionics www.radionics.com (781) 272-1233 Stryker Leibinger www.leibinger.com (616) 323-7700 Visualisation Technology www.vitech.com (800) 708-3856 Zeiss www.zeiss.com (914) 747-1800 z-kat www.z-kat.com (800) 522-3496

We then attach our instruments to the adapter clamps. As I perform the procedure, the camera on the main unit pinpoints the position of the instruments and the patient's face by tracking the position of the infrared markers on the adapter clamps and the headband. On the video monitor, I can see the three different CT views, the digital map of the patient's face, and a live endoscopic view. As I move my instruments, the system is able to display them on each CT scan and the digital contour map. It's like having an interactive CT image. In this way, I can see exactly where I am in the patient's anatomy.

The learning curve
One of the nice things about the image guided surgery system is that I don't have to change my technique to use it. The software has gone through several upgrades from when I first started using the system in 1995