Brain Imaging: MRI and CT

Imaging methods are used to look into whether there is a structural cause underlying the epilepsy. In this chapter, we explain the two most commonly used methods and the difference between them.

Magnetic Resonance Imaging (MRI)

MRI is the preferred imaging method in epilepsy investigation. Using a powerful magnet and radio waves, it creates very detailed cross-sectional images of the brain. It involves no radiation. MRI can show differences in brain development, past injuries, tumors, blood vessel structures, and many subtle structural changes. In a significant number of children with epilepsy, the MRI is normal; this is often a good sign.

What Is an MRI Scan Like?

The child is placed inside a tunnel-shaped machine. While it is running, the machine makes loud, repetitive noises; because of this, headphones or earplugs are provided. Most importantly, the child needs to lie still for a long time so the images come out clear. Since young children can't manage this, the MRI is often done under light sedation (being put to sleep) or anesthesia. This procedure is carried out safely by experienced teams; your doctor will explain the process in detail.

Preparing Before an MRI

If sedation is going to be used, the child needs to fast for the length of time your doctor specifies. Be sure to follow this instruction.

There must be no metal objects on or near the child (hair clips, snaps, metal buttons, toys). If there is a metal implant in the body, be sure to report it.

Before the scan, tell the child that the machine is “a big camera,” that it will make noise but won't hurt them.

Computed Tomography (CT)

CT uses X-rays to take images faster; but it is not as detailed as MRI, and it involves radiation. For this reason, it is generally not preferred for planned epilepsy investigation in children. CT is used more in emergencies — for example, after a head injury when there may be bleeding, or when an urgent situation needs to be ruled out quickly.

Is Imaging Always Necessary?

No. In some well-defined epilepsy syndromes with a good outlook (for example, typical childhood absence epilepsy or classic SeLECTS), a brain MRI is not always necessary, because these conditions are unlikely to be due to a structural cause. Your doctor makes the decision about imaging based on your child's particular situation. Every test has a reason; not doing unnecessary tests is also part of good medicine.