 When an abnormality of the brain is suspected, stereotactic (probing in three dimensions) brain needle biopsy is performed and guided precisely by a computer system to avoid serious complications.A small hole is drilled into the skull, and a needle is inserted into the brain tissue guided by computer-assisted imaging techniques (CT or MRI scans).Historically, the patient's head was held in a rigid frame to direct the probe into the brain; however, since the early 1990s, it has been possible to perform these biopsies without the frame.