5  Brain Imaging

5.1 Why Brain Imaging Matters

When someone has seizures, one of the first questions doctors ask is: “Is there something in the brain causing this?” Brain imaging helps answer that question by creating detailed pictures of the brain’s structure. These images can reveal abnormalities that might be responsible for seizures, such as scars, tumors, malformations, or areas of abnormal brain development.

Brain imaging is a crucial part of the epilepsy workup, but it’s important to understand what it can and cannot tell us. This chapter will explain the different types of brain scans, what to expect during these tests, and how to understand the results.

5.2 Types of Brain Imaging

5.2.1 MRI (Magnetic Resonance Imaging)

MRI is the gold standard for brain imaging in epilepsy. It provides the most detailed pictures of brain structure and is far better than CT for detecting subtle abnormalities that cause seizures.

How it works:

  • Uses powerful magnets and radio waves (no radiation)
  • Creates detailed cross-sectional images of the brain
  • Can be done with or without contrast dye

What it’s good at finding:

  • Hippocampal sclerosis (scarring in the memory center)
  • Cortical dysplasia (areas of abnormal brain development)
  • Brain tumors
  • Vascular malformations
  • Evidence of old strokes or injuries
  • Developmental abnormalities

Advantages:

  • No radiation exposure
  • Excellent detail and resolution
  • Can be repeated safely as needed
  • Multiple imaging sequences provide different information
  • Best test for identifying surgical targets

Limitations:

  • Requires lying still for extended periods
  • Can be claustrophobic for some people
  • Loud banging noises during scanning
  • Cannot be done if you have certain metal implants
  • Young children often need sedation

5.2.2 CT Scan (Computed Tomography)

CT scans use X-rays to create images of the brain. While not as detailed as MRI for most epilepsy purposes, CT has important roles in certain situations.

How it works:

  • Uses X-rays from multiple angles
  • Computer combines images into cross-sectional views
  • Can be done with or without contrast dye

When CT is used:

  • Emergency situations (fast and widely available)
  • When MRI is not possible (pacemakers, severe claustrophobia, metal implants)
  • To look for bleeding, acute injury, or calcifications
  • Sometimes as a first step before MRI

What it’s good at finding:

  • Bleeding in the brain
  • Skull fractures
  • Large tumors or masses
  • Calcium deposits
  • Hydrocephalus (fluid buildup)

Limitations:

  • Uses radiation (though low dose)
  • Less detailed than MRI for soft tissue
  • May miss subtle abnormalities that cause epilepsy
  • Not ideal for repeated imaging

5.2.3 Specialized Epilepsy MRI Protocols

Standard brain MRI protocols include common images most doctors need, but specialized epilepsy protocols provide more detailed information about areas commonly involved in epilepsy.

Features of an epilepsy MRI:

  • Thinner slices through the temporal lobes (where many seizures start)
  • Additional sequences optimized for subtle abnormalities
  • High-resolution views

5.2.4 MRI Field Strength

MRI machines are measured in Tesla (T). Higher strength can improve image detail.

1.5 Tesla (1.5T):

  • Standard strength, widely available
  • Less expensive and more accessible
  • Often adequate for initial evaluation

3 Tesla (3T):

  • Higher strength, better resolution
  • More sensitive for detecting subtle abnormalities
  • Preferred for epilepsy protocols when available
  • May find lesions missed on 1.5T
  • Better for detecting small cortical dysplasias
  • Can be noisier and feel warmer during scan

7 Tesla (7T):

  • Ultra-high strength, used in research or specialized centers
  • Exceptional detail, can detect very subtle abnormalities
  • Limited availability
  • Longer scan times
  • More restrictions on who can be scanned

5.2.5 Advanced and Specialized Imaging

PET scan (Positron Emission Tomography):

  • Shows brain metabolism (how brain cells use energy)
  • Identifies areas that work abnormally between seizures
  • Requires injection of radioactive tracer
  • Particularly useful when MRI doesn’t show clear abnormality
  • Often combined with MRI images (PET-MRI fusion)

SPECT scan (Single Photon Emission Computed Tomography):

  • Shows blood flow in the brain
  • Can be done during a seizure (ictal SPECT) to show seizure start
  • Requires injection of radioactive tracer
  • Mainly used in presurgical evaluation
  • Must be done in specialized epilepsy centers

fMRI (Functional MRI):

  • Maps brain areas responsible for speech, movement, memory
  • Helps plan surgery to avoid critical areas
  • Non-invasive
  • Patient performs tasks during scanning

MEG (Magnetoencephalography):

  • Records magnetic fields produced by brain electrical activity
  • Combines features of EEG and imaging
  • Helps localize seizure focus for surgery planning
  • Available only at specialized centers
  • Completely non-invasive

5.3 What to Expect During an MRI

5.3.1 Before the Scan

Preparation:

  • No special dietary restrictions
  • Take regular medications
  • Wear comfortable clothing without metal fasteners
  • Remove all metal objects (jewelry, watches, hairpins, glasses)
  • Leave electronics and credit cards in a safe place

Important questions you’ll be asked:

  • Metal implants (pacemaker, aneurysm clips, cochlear implants)
  • Previous surgeries with metal plates or screws
  • Metal fragments in your eyes
  • Pregnancy status
  • Tattoos (some old tattoos contain metal)
  • Claustrophobia
Metal and MRI Don’t Mix

The MRI machine has a powerful magnet that is always on. Metal objects can become dangerous projectiles. Report all metal in or on your body. When in doubt, tell the technician—they can determine if it’s safe.

For children:

  • Explain what will happen in age-appropriate terms
  • Practice lying still at home
  • Bring comfort items if allowed
  • Some centers offer child life specialists
  • Sedation or anesthesia may be needed for young children or those with developmental differences

5.3.2 During the Scan

  1. Lie on a sliding table
  2. Head positioned in a special coil
  3. Earplugs or headphones provided
  4. Table slides into the tunnel
  5. Lie completely still
  6. Scan involves different sequences with different sounds
  7. Contrast injected if needed

What you’ll experience:

  • Loud banging, knocking, buzzing
  • Need to lie still for 30-60 minutes
  • Confined space (can be claustrophobic)
  • Cool air circulation
  • Communication via intercom
  • Music if available

If claustrophobic:

  • Tell staff beforehand
  • Medication may be offered
  • Keep eyes closed, use breathing exercises
  • Open or wide-bore MRI may be available
  • You can stop the scan at any time

Contrast dye (gadolinium):

  • Not always necessary
  • Injected through IV if used
  • Helps identify tumors, inflammation, blood vessel abnormalities
  • Generally very safe
  • Rare allergic reactions
  • Excreted by kidneys within 24 hours

5.3.3 After the Scan

  • No recovery time needed
  • Resume normal activities immediately
  • Results typically available within days to a week

5.4 What to Expect During a CT Scan

Process:

  • Remove metal objects
  • Lie on sliding table
  • Table moves through donut-shaped scanner
  • Hold still for 5-10 minutes
  • Contrast may cause warm or metallic taste

After scan:

  • Leave immediately
  • No restrictions
  • Drink extra fluids if contrast used

5.5 Understanding Your Imaging Results

5.5.1 What “Normal” Means

A normal brain MRI means no structural abnormalities were seen. This is common in epilepsy (20-30% of people).

Important points:

  • Doesn’t mean you don’t have epilepsy
  • Doesn’t mean seizures aren’t real
  • Some causes are too subtle to see
  • Abnormalities may be microscopic
  • EEG and clinical history remain important

MRI-negative epilepsy: Some people have normal MRIs but clear epilepsy.

5.5.2 Incidental Findings

  • Small cysts or variants
  • Minor blood vessel variants
  • Sinus problems
  • Age-related changes
  • Areas that need follow-up

5.5.3 How Imaging Affects Treatment

If imaging shows a clear cause:

  • May influence medication choice
  • Helps predict seizure control
  • Determines if surgery is an option
  • Provides prognostic information
  • May identify genetic syndromes

If imaging is normal:

  • Treatment still needed
  • Medications work regardless of cause
  • Focus on EEG findings and seizure type
  • Surgery less likely but possible

5.5.4 Imaging and Surgery Planning

If surgery is being considered (@sec-presurgical-evaluation):

  • Identifies tissue to be removed
  • Shows relationship to critical brain areas
  • Helps predict surgical outcome
  • Combines with EEG, PET, neuropsych tests
  • May require specialized imaging protocols