Intraoperative Diagnostics

In the beginning there was the idea

It is precisely in neurosurgery where intraoperative diagnostics was ‘invented,’ so to speak, due to its especially sensitive OR fields. It helps, for example, to understand intraoperatively every volume displacement of the “shifting” brain tissue when a brain tumor is removed. It also allows, via resection controls during surgery, verification that the tumor has been fully removed even though the intervention was minimally invasive, thus eliminating the need to carry out another, possibly unnecessary, intervention.

This makes treatment safer and improves the course of the operation for patient and surgeon. Yet whether it’s done with ultrasound, CT or MRI, the best possible multidisciplinary solution — for neurosurgery or accident surgery as well as for orthopedics, urology or otorhinolaryngology — did not exist until now. Professor Jörg-Christian Tonn, Professor Karl-Walter Jauch and Professor Maximilian Reiser from the Department of Neurosurgery, Surgery and Radiology at the University Hospital were aware of this and had a plan. Their idea: Establish a research cooperation initiative in which all pieces of equipment needed for intraoperative diagnostics and their mutual interaction be tested within a pre-defined period and further developed according to clinical demands. “The project should provide us with the varied possibilities that modern computer tomography with its expanded software options can offer to the OR nowadays for the various surgical specializations,” says Professor Tonn. The University Hospital found the right project sponsors and development partners in Siemens, BrainLab and TRUMPF. The three companies took up the challenge, supplying their products and further development free of charge and putting themselves at the service of the project. The research OR opened its doors in January of this year.

Scanning as a scan can

Back to the OR, Dr. Uhl and his team have removed a tumor. They now want to perform an intraoperative scan to be sure that removal has been successful. The OR team leaves the room, leaving the anesthesiologist inside. The carbon surgical table that allows radiation to go through is moved to the pre-determined scanning position, and then it’s the CT scanner’s turn. Layer by layer, every 14 seconds, it takes new reference images including vessel structures and blood flow measurements. It transfers

the data to the navigation system made by BrainLab, so it can translate them into a 3D image. Owing to the fact that during surgery the infrared camera has been keeping an eye on the instruments’ positions and paths with the help of optical sensors, the surgeon always sees on the monitor where in the surgical region he is within one millimeter. This allows him to operate safely in inaccessible areas.

Yet the new solution allows even more, namely the registration of intraoperative CT data in spite of the fact that the patient is fully and aseptically covered. Thanks to this capability, the patient’s head markings, that until now were essential as registration references, will soon be unnecessary. The role of the head markings is now undertaken by markings on the front of the CT scanner and by a star-shaped reference object on the surgical table next to the patient’s head. From this spatial “triangular” ratio the reference points have with each other, the software calculates the position of the CT during each picture, places the CT in relation to the patient’s position in the room and creates a 3D image for the surgeon. So no radiation or stripe artifacts — caused by metal, for example — can spoil the image, the reference star is also made of carbon. During surgery the software then visualizes the spatial relationships between instruments and reference star and also allows the surgeon to “match” the intraoperative CT images with the previously created MRI images.