MRI Brain Protocol for Epilepsy Evaluation
For patients being evaluated for epilepsy, use a dedicated epilepsy MRI protocol that includes high-resolution 3D T1-weighted imaging with 1-mm isotropic voxels, thin-cut (≤3 mm) coronal T2 and FLAIR sequences in hippocampal angulation, and sequences optimized for detecting hippocampal pathology and cortical malformations. 1
Core Protocol Components (HARNESS-MRI)
The International League Against Epilepsy recommends the HARNESS-MRI protocol as the standard approach, which includes:
Essential Sequences
- 3D T1-weighted volumetric acquisition (gradient echo): 1-mm isotropic voxels for detecting cortical malformations 1
- Coronal T2-weighted imaging: ≤3 mm slice thickness, perpendicular to hippocampal long axis 1
- Coronal FLAIR sequences: ≤3 mm slice thickness in hippocampal angulation 1
- Axial or 3D FLAIR: For detecting signal abnormalities 1
- Hemosiderin/calcification-sensitive sequences (gradient echo or susceptibility-weighted imaging) 2
Critical Technical Requirements
Slice thickness matters significantly: T2 and FLAIR sequences must not exceed 3 mm thickness to detect small epileptogenic lesions 2. The 3D T1 acquisition should use 1-mm isotropic voxels 1.
Multiple orientations are mandatory: Acquire at least two slice orientations each for T2 and FLAIR in hippocampal angulation, as hippocampal sclerosis is the most common cause of temporal lobe seizures 1.
Field Strength Considerations
Use 3T MRI whenever possible, particularly for intractable seizures or refractory epilepsy, as it provides superior sensitivity (84%) compared to CT (62%) 3. Patients with normal 1.5T scans may have lesions identified on repeat 3T imaging 1.
Contrast Administration
Intravenous contrast is NOT routinely necessary 1. However, administer contrast when:
- Initial non-contrast images are insufficient
- Neoplasm is suspected
- Inflammatory conditions are being considered 1
When to Perform MRI
High-Priority Indications
Obtain MRI urgently in patients with:
- Focal findings on neurological examination 1
- Persistent headache
- Recent head trauma 1
- Abnormalities on EEG correlating with high probability of structural abnormalities 1
- Focal seizures (50% positivity rate vs. 6% for generalized seizures) 3
Lower Priority
Some epilepsy forms have low MRI yield and imaging may be deferred:
- Primary generalized epilepsy with typical features
- Benign focal epilepsies of childhood with characteristic EEG
- Early onset childhood epilepsy with occipital spikes and adequate antiepileptic drug response 1
Special Populations
Intractable/Refractory Epilepsy
For surgical candidates, the protocol should include both anatomical and functional imaging. MRI sensitivity reaches 84% in this population 3. Consider adding FDG-PET when MRI is normal or shows nonspecific findings, as PET demonstrates 63-67% sensitivity for lesion localization and 94% specificity in nonlesional MRI cases 3.
Pediatric Patients
Use the same dedicated epilepsy protocol. CT has limited utility (only 6% positive in generalized seizures vs. nearly 50% in focal epilepsy) 3.
Common Pitfalls to Avoid
- Don't use "standard head" MRI protocols - they frequently miss therapeutically relevant epileptogenic lesions 2
- Don't skip hippocampal-oriented sequences - standard axial-only imaging misses hippocampal pathology
- Don't accept thick slices - sequences >3 mm will miss small cortical dysplasias and subtle hippocampal abnormalities
- Don't adapt protocol to clinical hypothesis - use comprehensive protocol regardless of suspected focus 2
Role of CT
CT is NOT appropriate for routine epilepsy evaluation with only 30% detection rate for focal lesions 1. Reserve CT for: