Scans generate images of the brain for the purpose of diagnosing tumors. They take the place of x-rays, which do not show tumors located behind the bones of the skull or spine. The most common scans for diagnosis and follow-up are magnetic resonance imaging (MRI) and computerized tomography (CT).
Certain types of brain scans use a special dye, called contrast, to help areas of interest show up better. Contrast dye is usually injected into the body before the scan starts. With the exception of those requiring an injection of contrast dye, scans are relatively painless—like getting a picture taken. The hardest part for some people is to sit or lie still for a long time.
The purpose of a scan is to give your doctor a closer look at your brain and to provide information that will assist in your diagnosis. Scanning techniques include:
Computed Tomography (CT): This scan combines an x-ray-type device with a computer. The patient lies on a table that slides into a doughnut-shaped opening in a scanning device. The CT scanner circles the head so that x-rays penetrate the brain from many directions. Thousands of x-ray readings are then fed into the computer, which brings the information together into a picture of the brain.
Magnetic Resonance Imaging (MRI): The MRI scanner is a tunnel-shaped piece of equipment. The patient lies on a table that slides into the scanner, where a magnetic field surrounds the head. Signals are generated from the magnetic field and fed into a computer, which creates a picture of the brain.
Flow-Sensitive MRI (FS MRI): This type of combines functional MRI with images of cerebrospinal fluid (CSF) flow. FS MRI can be useful in planning the surgical removal of a skull base tumor, spinal cord tumor, or a tumor causing hydrocephalus (fluid buildup on the brain).
Functional MRI (fMRI): fMRI produces MRI images in a faster sequence than traditional MRI. The increased speed shows how oxygen is used in the brain. Prior to or during surgery, fMRI may be useful for showing which areas of the brain control important functions so that these areas can be avoided during the procedure.
Dynamic CT or Dynamic MRI: Advances in computer technology have made it possible to use existing scanning equipment to measure cerebral blood volume (CBV) and cerebral blood flow (CBF). Contrast dye is injected, and the scanner immediately starts taking pictures. These new methods provide even better tools for diagnosis.
Angiography and MRI Angiography (MRA): Angiography is used to outline the presence and position of blood vessels in the brain. MRA uses a rapid series of MRI scans to follow the blood flow. It can be done with or without the injection of contrast dye.
Magnetic Resonance Spectroscopy (MRS): MRS produces images that show function rather than shape. This technique can show patterns of activity that may be helpful in diagnosing specific tumors and conditions. This technique may also be used to determine how advanced a tumor is.
Positron Emission Tomography (PET, FDG-PET): PET is not usually used for diagnosis, but it can help your doctor determine the grade of your tumor. In some cases, it may also be used to tell the difference between recurrent tumor cells, cells killed by radiation, and scar tissue.
Single Photon Emission Computerized Tomography (SPECT): SPECT is not usually used to diagnose brain tumors. However, it sometimes provides data that complements information captured in other scans.
Magnetoencephalography (MEG): This scan measures the magnetic fields created by nerve cells. No physical contact is required to record these signals. MEG is often used in combination with information from other types of scans.