The Utilisation of Ultrasound for Navigation in Neurosurgery

Intraoperative sonography (IOS) in neurosurgery is a standard acquisition tool for real-time imaging of brain tissue and target structures. The technological advance of ultrasound devices has led to miniaturisation of ultrasound probes and enabled their use in the limited space of craniotomy. The quality of IOS imaging improved after introducing high-frequency probes with high spatial resolution. The environment of brain tissue provides favourable insonation conditions and enables precise localisation and navigation of surgical access to all common brain tumours, including gliomas, metastases, meningiomas and cavernomas. The basic imaging is B-mode (two-dimensional; 2D) and can be supplemented by 3D (three-dimensional; 3D) reconstruction to improve orientation. Brain tumours are displayed as hyperechoic structures compared to the brain tissue. The integration of ultrasound devices with optical neuronavigation facilitates the orientation in IOS even more. Besides the navigational function, the IOS is suitable for detection and localisation of tumour remnants during removal of gliomas and metastases. In this way the IOS contributes to maximum extent of resection. The contrast-enhanced IOS further improves image quality and reduces the impact of artefacts. Duplex ultrasonography using colour Doppler or power Doppler makes it possible to localise vessels and to evaluate their relation to the tumour or to localise its vessel supply. In addition to localisation of tumours, it is possible to assess their internal structure and lead biopsies and navigate access. The main advantages of IOS are precise real-time information, availability, easy repeatability and high-quality imaging. The prerequisite for effective IOS imaging is long-term experience with this imaging modality. The drawbacks of the IOS include the impossibility to navigate craniotomy and the occurrence of artefacts during resection control.