Intraoperative three-dimensional ultrasonography: an approach to register brain shift using multidimensional image processing.

Neuronavigation uses the skull as a reference system for transfer of image-space data to physical space during brain surgery. This requires a stable spatial relation between the skull and intracranial structures. However, especially dura opening and preparation for lesion removal causes brain shift. This shift may mislead the surgeon unless preoperatively defined image-space data are corrected for shifting online intraoperatively. Since a real-time modality is required intraoperatively, we propose three-dimensional (3 D) ultrasonography for detection of brain shift. By coupling common ultrasound probes (3.5/6.5 MHz) to a magnetic digitizer receiver 2 D-ultrasound scans were obtained intraoperatively along with their spatial orientation. 3 D-ultrasonography was achieved by alignment of sequentially obtained 2 D-scans. For multimodal matching, preoperative MRI data was segmented for landmarks (cerebral ventricles, lesion) automatically. The 3 D-ultrasonography data set scanned intraoperatively was contoured and matched with the MRI data set. Intraoperative 3 D-ultrasonography revealed excellent delineation of landmarks in almost real time in six patients studied. Matching of MRI data and intraoperative 3 D-ultrasonography data was successful with good correspondence of landmarks. Intraoperative 3 D-ultrasonography is proposed as a promising tool for on-line detection of brain shift during intracranial operations.