Head scans, including CT and MRI, are noninvasive methods of imaging the brain, skull, and other tissues. CT scans use X-rays and are preferred in emergency situations, while MRI scans use magnets and radio waves and can provide more detailed images. Both scans can diagnose and monitor various conditions.
The term head scan can refer to a cranial computed tomography (CT) or magnetic resonance imaging (MRI) scan of the head. Both CT scans and MRIs are noninvasive methods of making images of a patient’s head, including the brain, skull, and other tissues. Each type of head scan is painless and provides your doctor with important information for diagnosing a variety of conditions.
A cranial CT scan uses X-rays to create special cross-sectional images from the top of the neck to the top of the head. To perform this head scan, the patient must lie down on a table that slides into the CT scanner. As the patient lies inside the scanner, the X-ray beam circulates around the body to help create individual images, called slices. Contrast dye can be injected into a vein to highlight blood vessels or look for a tumor. Head CT is used to help diagnose and monitor various conditions, including a brain tumor, brain infection, hydrocephalus, and bleeding in the brain.
An MRI of the head uses magnets and radio waves, instead of radiation, to create images of the inside of the head. A magnetic field created by the MRI scanner forces the hydrogen atoms in the patient’s body to assemble in a particular way. When the scanner sends out radio waves, they bounce off hydrogen atoms and a computer records their response, creating images, also known as slices.
To perform this type of head scan, the patient will also need to lie down on a table that slides into a scanner. Small receivers, called coils, are placed around the head to help transmit radio waves. An IV contrast dye may also be used during an MRI to make the images clearer. An MRI scan of the head can be used to diagnose and monitor a variety of conditions, including brain tumors, brain infections, multiple sclerosis, and abnormal brain development.
A scan of the head is typically done using computed tomography when time is a factor, as CT scans take only minutes to complete, while MRI scans can take up to an hour. CT scanners are also usually available in the emergency rooms of most hospitals. Examples of cases where a CT scan of the head may be preferable include when the patient has initial symptoms of a stroke, acute trauma to the face and head, or bleeding into the brain. An MRI of the head, however, may be preferred to help provide insight into areas of the brain that are difficult to see on a CT scan. A scan of the head using MRI can also show blood vessels, blood flow, and fluid surrounding the spinal cord and brain.
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