Iplan 2

MRI scans were performed using a 1.5 Tesla scanner (Siemens Espree, Erlangen, Germany). The DTI data was acquired with single-shot spin-echo diffusion-weighted echo-planar sequence (TE 147 ms, TR 9400 ms, matrix size 128 × 128, FOV 251 × 251 mm, slice thickness 3 mm). The diffusion-weighting (high b value) was 1000 s/mm 2 . 12 gradient directions were obtained. The voxel size was 1.9 × 1.9 × 3 mm. Applying five averages; the total DTI measurement required 10 min. The anatomic images were obtained by T1WI 3D MPRAGE sequence (TE 3.02 ms, TR 1650 ms, matrix size 256 × 256, FOV 250 × 250 mm, slice thickness 1 mm). Intraoperative DT imaging was performed using the same SS-EPI sequence after tumor removal. Further T1WI MPRAGE scanning was also performed to record changes of brain tissue. All data were transferred to the planning software (iPlan 2.6, BrainLab, Feldkirchen, Germany) for processing. DTI data was directly imported into the iPlan. FA and tensor map were calculated automatically. Anatomic datasets were converted and exported to iPlan using PatXfer 5.2 (BrainLab, Feldkirchen, Germany). These sequences were co-registered by a semiautomatic rigid registration algorithm for further processing.

Details of the intraoperative workflow and setup have been published before. 13, 21 In summary, imaging started after inducing general anesthesia and rotating the patient into the iopMRI scanner (1.5-T MRI, Magnetom Sonata Maestro Class, Siemens Medical Solutions). The intraoperative sequences were acquired as described previously. 21, 22 Overall, the mean intraoperative scanning time was 13.9 minutes. The data set was fused with preoperative functional MRI data using our neuronavigation software (iPlan 2.6, Brainlab AG). We used the T2-weighted images for segmentation of the lesion and coregistration of functional data (Fig. 1). After planning the ideal trajectory, we transferred the navigation plan to the surgical microscope (OPMI Pentero, Zeiss). Coregistration of preopera-tive and initial intraoperative MRI sequences with anatomical structures was performed with a median error of 1.4 ± 0.7 mm of the navigation system.

Using the iPlan 2.6 neuronavigation software (Brainlab AG), we screened the appropriate initial intraoperative T2-weighted MR images and segmented each lesion man- ually in every axis using the ruler function of the software. The resulting tumor volume was calculated by the software and was defined as the maximum tumor mass that could be achieved for GTR.
We defined subtotal resection as a volume reduction of 90%-99% and GTR as complete removal of the segmented tumor mass. In cases of re-resection, remnant tumor volume was measured by comparing the corresponding initial preoperative and intraoperative MR images, and a new outline of the remaining tumor contours was obtained using our neuronavigation software.