The treatment of a specific subtype of highly malignant brain tumor (called "glioblastoma" or "glioblastoma multiforme") consists of neurosurgical resection, followed by radiotherapy and mostly chemotherapy as well. Increased extent of tumor resection is associated with prolonged survival. The standard treatment uses conventional neuronavigation systems to increase extent of tumor resection. However, the quality of this form of neuronavigation decreases throughout surgery because of "brain shift". This is caused by edema, loss of cerebrospinal fluid and tumor resection. A new form of neuronavigation uses intraoperative MRI to compensate for brain shift, and to check for the presence of residual tumor that can be removed.