Pre- and intraoperative imaging in cranial surgery was performed using a collimation of 24 × 1.2 mm, in pituitary surgery of 40 × 0.6 mm at 120 kV, 320 mAs, pitch 0.9 and a rotation time of 1 s. Reconstructions were performed with a slice thickness of 0.6, 1.0, 1.5, 2 and 5 mm. If necessary contrast media were given via an automated infusion pump (Stellant MEDRAD Inc., Indianola, Pennsylvania, USA) with a weight-adapted contrast agent injection protocol followed by a saline chaser (1.4 ml contrast agent per 1 kg bodyweight Imeron 300 (Bracco-Altana Pharma, Konstanz, Germany) and 0.42 g iodine per 1 kg bodyweight at an injection rate of 0.035 × bodyweight ml/s followed by 100 ml saline at 0.035 × bodyweight ml/s, respectively). For CT angiography a collimation of 40 × 0.6 mm was used at 120 kV, 120 mAs, pitch 1.1 and rotation time of 1 s. Contrast agent injection was done by using an automated infusion pump with a dedicated protocol (1.35 ml contrast agent per 1 kg bodyweight Imeron 300 (Bracco-Altana Pharma, Konstanz, Germany) and 0.4 g iodine per 1 kg bodyweight at an injection rate of 6.0 ml/s followed by 100 ml saline at 6.0 ml/s, respectively). For image reconstructions a slice thickness of 1.0 mm and an increment of 0.75 mm were used. Multiplanar reconstructions; maximum intensity projections in axial, coronal and sagittal orientations; and reconstructions using volume-rendering technique were used. For cerebral perfusion measurements a standard contrast agent injection protocol was used, and one scan was performed every second over a time period of 40s using 80 kV and 200 mAs with a collimation of 24 × 1.2 mm. Perfusion scanning started 5 s after injection of 50 ml contrast agent (Imeron 300) at 7 ml/s and a saline flush of 50 ml at 7 ml/s. After acquisition standard perfusion analysis was performed using a standard workstation (Syngo MMWP, Siemens Medical Solutions, Erlangen, Germany) and colour-coded parameter maps of cerebral blood flow, cerebral blood volume and time to peak were calculated Fig. 39.3.

In spinal surgery a non-enhanced protocol was used for spondylodesis and a contrast-enhanced protocol for tumour surgery. Scans were performed using a collimation of 24 × 1.2 mm at 120 kV, 240 mAs, pitch 0.9 and a rotation time of 1 s, using automated dose-modulation software. MPR reconstructions with a slice thickness of 3 mm were calculated in axial and sagittal orientations.

Beginning January 2006 until March 2008, 240 neurosurgical patients with a mean age of 55 ± 17 years were operated with the help of iCT. There were 146 cranial (105 tumours, 10 patients with unruptured aneurysms) and 94 navigated spinal stabilisation operations. As the system was used in a multidisciplinary OR, trauma surgery was also performed but is not reported here. In cranial surgery, iCT was used for automated navigation, intraoperative control of tumour resection, intraoperative CT angiography and measurement of cerebral blood flow in aneurysm surgery. In spinal surgery, the system was predominantly used for navigated instrumentation and intraoperative control of correct placement of screws and other implants.

Surgical and anaesthesiological set-up, intraoperative workflow, technical problems of iCT and integration of the navigation system were recorded. Times required for preoperative scanning (preoperative CT, safety checkup, data transfer, registration of navigation system) and intraoperative scanning (sterile draping, scan, resumption of surgery) for each procedure were assessed by a person not directly involved in the surgical procedure. Quality of intraoperative imaging with special regard to artefacts was assessed. Change of surgery based on intraoperative imaging was documented for each procedure. An intraoperative CT was obtained to assess the extent of decompression and the accuracy of instrumentation. All screws were evaluated on multiplanar reconstructions and rated on the basis of a 2-mm increment classification suggested by Gertzbein and Robbins [5].