The term head scan can either refer to a cranial computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan of the head. Both the CT scan and the MRI scan are non-invasive methods to make pictures of a patient's head, including the brain, skull, and other tissues. Each type of head scan is painless and provides the physician with important information to diagnose a variety of conditions.
A cranial CT scan uses x-rays to make special cross-sectional images from the upper portion of the neck to the top of the head. To perform this head scan, the patient must lie on a table that slides into the CT scanner. While the patient lies inside the scanner, the x-ray beam circulates around the body to help make individual images, called slices. Contrast dye may be injected into a vein to highlight blood vessels or look for a tumor. Cranial CT is used to help diagnose and monitor various conditions, including a brain tumor, brain infection, hydrocephalus, and bleeding in the brain.
A head MRI uses magnets and radio waves, instead of radiation, to create pictures of the inside of the head. A magnetic field created by the MRI scanner forces hydrogen atoms in the patient's body to assemble in a particular manner. When the scanner sends out radio waves, they bounce off of the hydrogen atoms and a computer records their response, which create images, also known as slices.
To perform this type of head scan, the patient will also need to lie on a table that slides into a scanner. Small receivers, called coils, are arranged around the head to help the transmission of the radio waves. An IV contrast dye can also be used during a MRI to make the images clearer. A head MRI may be used to help diagnose and monitor a variety of conditions, including brain tumors, brain infections, multiple sclerosis, and abnormal brain development.
A head scan is typically performed using computed tomography when time is a factor, as CT scans only take a few minutes to complete, whereas MRI scans can take up to an hour. CT scanners are also usually available in most hospitals' emergency rooms. Examples of cases when a head CT scan may be preferable include when the patient has beginning symptoms of a stroke, acute trauma of the face and head, or bleeding in the brain. A MRI head scan, however, may be preferred to help give information about areas of the brain that are difficult to see on a CT scan. A head scan using magnetic resonance imaging can also show blood vessels, blood flow, and fluid that surrounds the spinal cord and brain.