Surgical Navigation With Intraoperative Imaging: Special Operating Room Concepts

Introduction

One of the most challenging developments in neurosurgery encompasses the interdisciplinary effort to integrate microneurosurgery and technology, in particular imaging. Neurosurgical techniques have reached a high level of sophistication. Increasing understanding of neurophysiology as well as neuropathology, precise preoperative imaging, small tailored approaches, and specialized instruments, as well as detailed monitoring techniques have led to improved results, and generated higher standards and demands for safety and outcome.

But there were no intraoperative means to confirm the surgeon’s impression, whether the surgical objective was achieved. Postoperative imaging for neurooncologic, neurovascular, and instrumented spine surgery demonstrated the need to obtain intraoperative quality assurance.

For high-grade gliomas, Albert et al. (1994) reported that postoperative imaging showed tumor remnants in 77% of patients who were presumed to have undergone gross total resection. In 2006 Stummer et al. published a multicenter randomized study, which showed residual tumor in 64% of the control group (patients undergoing standard conventional microsurgical tumor resection). Since the importance of the extent of resection for high- as well as low-grade gliomas has been documented, these findings emphasize the need for objective intraoperative resection control.

In neurovascular surgery the routine use of intraoperative angiography has been advocated to avoid undetected residual disease. ^,

In spinal surgery, even with modern navigation techniques in addition to conventional imaging, misplaced screws are found in approximately 5%.

Thus various surgical groups proceeded to integrate imaging into their procedures.

The earliest attempts to image intraoperatively beyond plain x-ray were made with ultrasound (US) and computed tomography (CT). The immediate impact on surgical procedures was small. The resolution (US and CT) was limited and the integration into the operating room cumbersome (CT). Another avenue opened with the introduction of image-guided neuronavigation (IGN) systems. ^, These systems allowed the transfer of increasingly refined presurgical image information into the operating theater to guide surgical procedures. However, intraoperative changes (“brain shift”) critically limited their application accuracy. ^, To overcome this limitation the concept of intraoperative imaging resurfaced. With magnetic resonance (MRI) becoming the method of choice for the imaging of the central nervous system, pioneering efforts introduced this modality into surgery. These initial experiences with intraoperative MRI (iMRI) ignited a rapidly evolving field with interesting diversification.

The integration of surgery and imaging technology, especially MRI, demands consideration of safety, as well as procedural and architectural issues. In this chapter, we focus on those imaging technologies that have resulted in modified operating room (OR) designs and changes in the surgical workflow as well as the development it sparked.

Computer-Assisted Image-Guided Neuronavigation

The major link between imaging and integration of this information into surgery is provided by navigation systems.

Diagnostic computer-based image analysis and three-dimensional (3D) modeling facilitated the spatial definition of complex pathologic processes. The desire to use this information directly in the surgical field to facilitate surgical decision making led to the introduction of IGN systems in the mid-1980s ^, and their commercial availability in the early 1990s. These systems provided the surgeon with a tool that allowed the transfer of presurgical image information in an intuitive and interactive fashion into the surgical field.

Meanwhile, the technology has proceeded from being a novelty to an established asset for neurosurgical procedures. Questions of application accuracy and integration of instruments were overcome. However, the major shortcoming was the dependence on preoperative image data. Since intraoperative changes (e.g., CSF drainage, tumor resection, sagging of the cortex, swelling of underlying tissue, summarized as “brain shift”) accumulate throughout surgery, preoperative information is progressively invalidated. ^{, ,} This has particular impact on glioma surgery. While enabling precise approach, planning, and localization, resection control is generally beyond the capacity of these systems, since they cannot account for intraoperative changes and deformations. Intraoperative imaging resolved this issue directly as it enabled continued use of these systems with the newly acquired accurate data.

Mathematical models investigate a different avenue to compensate for various brain shift patterns. Various algorithms characterize and calculate deformation matrixes. ^{, ,} Various “brain shift” patterns were identified. A multimodal approach uses intraoperative “sparse” US data to calculate a deformation matrix, which is then used to elastically deform preoperative MRI images.

Intraoperative Imaging

We provide an overview and comprehensive organizational framework for imaging modalities that influence surgical workflow and OR-suite design.

Intraoperative Computed Tomography

Shalit et al. and Lundsford first reported the integration of a stationary CT into the operation room. ^, The next generation of CTs was mobile, permitting shared application in the OR and ICU. However, image quality and radiation exposure limited the application and further implementation of this modality. Further advances in CT- and OR-table technology and integration with navigation systems have led to a reappraisal.

Modern CT-OR ( Fig. 2.1 ) solutions use a rail system to move the CT between a parking position and the patient for scanning which provides full access to the patient. In spine surgery, intraoperatively acquired images can be used to update navigation systems and to guide and confirm correct positioning. For neurovascular surgery, intraoperative CT-angiography has the potential to provide information on obtained occlusion of vascular pathologies, but also with perfusion CT on potential vascular compromise.

For the definition of brain tumors—particularly low-grade lesions, but also high-grade gliomas—the intraoperative imaging quality remains less informative. Gross total surgical resection may be documented, but the sensitivity to detect residual tumor, even with the present CT generation, remains inferior to MRI. Furthermore, cumulative radiation exposure limits the number of potential intraoperative scans. Despite these limitations, further developments have arisen such as having two surgical suits served by one CT mounted on rails, equivalent to the “shared resources” design described for MRI below, and scanners with larger aperture.