Accurate organ or tumour localization and precise guidance within the patient's body can mean a useful help to the surgeon during delicate interventions in the operating theatre. Researchers from the Centre for Orthopaedic Research at the Shadyside Hospital in Pittsburgh have worked out a prototype system for 3D image overlay, allowing the physician to view medical images or computer enhanced graphics overlaid on the patient and simultaneously registered with his body. This technique can even be applied for teleguidance of medical staff, situated at remote sites.
The system consists of four elements. The surgeon is able to see the patient through a half-silvered mirror, a so-called beam splitter, which is transparent and reflective at the same time. A display device, whether a monitor or a video projector, is being installed above the beam splitter. As a result, a reflection of the video display appears to be floating inside the surgical field through the beam splitter. The physician wears a pair of liquid crystal shutter glasses, enabling him to view stereo images. The overlay device incorporates a head tracking system with six degrees of freedom, in order to change the viewpoint without losing the right perspective.
Especially in microsurgery, neurosurgery, obstetrics, orthopaedics, and plastic surgery, image overlay may provide an excellent tool to render pre-operatively prepared images, to help the surgeon perform the intervention according to the initial plan. Currently, the Pittsburgh team is designing a smaller and mobile system for practical use in the operating room. The new model will be easier to remove from the operating table, if needed, to offer the surgeon more ready access to the patient. Image overlay can also be used in Interventional Magnetic Resonance Imaging (IMRI) systems in combination with an IMRI scanner, to provide the physician with almost real time medical images.
In addition, the 3D image overlay technique constitutes a beautiful asset in telemedicine applications. Medical staff at remote sites can accurately be guided through difficult procedures by an expert surgeon, displaying 3D graphics with image overlay. Normal conditions, such as teleconsultations or rural health care delivery are easy to imagine but the research team even considers crisis situations like battlefield trauma care, disaster relief and assistance to developing countries.
Distant guidance of telerobotic systems with image overlay is possible but not advisable, according to the Pittsburgh group. The total exclusion of human intervention at the remote site is not quite accepted by the medical establishment. The guidance via image overlay of a proper medical staff instead of a robot includes a higher degree of safety and flexibility while being less expensive at the same time. For illustrated information about the image overlay system, we refer to the Web site of the Centre for Orthopaedic Research.