This approach has so far been used in a variety of surgical procedures, including the implantation of multiple depth electrodes for the recording of EEG signals during the work-up to epilepsy surgery, the resection of tumours, and the removal of brain tissue for the treatment of intractable epilepsy. In general, data sets from all modalities are not employed for every patient; rather, data set selection is based on the particulars of the case.
In our clinical environment MRI images are typically acquired as an isotropically resolved volume with voxel dimension approximately mm. This slice data is segmented using software on an ISG Allegro system to enable the patient's skin surface and other structures of interest to be visualized. When required MRA images are collected during the same session although usually to a lower resolution. Collecting this data and displaying it with MIP rendering techniques allows a representation of the 3-D vasculature to be obtained without recourse to segmentation.
In cases where it is appropriate, stereoscopic DSA projections are acquired by angulating the x-ray gantry by seven degrees between views. Composite arterial/venous images are formed by subtracting the maximally filled arterial and venous data for each eye view, giving images in which the arteries and veins are distinguished from each other by their opposing contrasts, while simultaneously achieving the required suppression of the background.
When PET is used, we typically acquire 45 slices 6.3mm thick, overlapped to yield an effective spacing of 3mm. As part of the procedure used to register these images to the MRI data, they are scaled and re-interpolated to the same resolution and pixel size as the MRI data sets. This facilitates the matching of the two data sets on a pixel-by-pixel basis.