Epilepsy protocol (MRI)

MRI protocol for epilepsy is a set of MRI sequences aimed at improving sensitivity and specificity in identifying possible structural abnormalities that underlie epilepsy (e.g. mesial temporal sclerosis and malformation of cortical development). 

Perhaps more than most other MRI protocols, studies aimed at investigating epilepsy are heterogeneous, depending not only on local preference but, due to heavy reliance on high-resolution imaging, the constraints of the available scanner.

Generally, fewer high-quality sequences are preferable to more numerous lower-resolution sequences (e.g. HARNESS‐MRI protocol ⁷).

Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist and referrer preference, institutional protocols, patient factors (e.g., allergy), and time constraints. 

Sequences

A standard protocol to investigate patients with seizures will depend on the limitations of available scanners. High-quality T1 and FLAIR whole brain acquisitions, with dedicated even higher resolution angled coronal T2 through the hippocampi at the core of all modern epilepsy protocols ^4,6,7:

• T1

  • sequence

    • 3D ≤1mm isotropic acquisition

    • planes: axial (AC-PC), sagittal and coronal

    • read more: T1 weighted imaging

  • purpose

    • visualize brain anatomy, morphology and volume

    • measuring cortical thickness and appreciating grey-white matter differentiation

    • visualize any unusual location of grey matter as in grey matter heterotopia 

    • visualize any abnormal sulcation

• FLAIR

  • sequence

    • ≤3mm (or 3D isotropic if available)

    • read more: FLAIR

  • planes: axial (AC-PC) and coronal

  • purpose

    • look for cortical or subcortical hyperintensities (e.g. radial glial bands, infarcts, demyelination, abnormal cortex etc...)

    • identify focal lesions (e.g. tumors)

• T2

  • sequence:

    • ≤1mm inplane resolution (as low as possible)

    • read more: T2 weighted imaging

  • plane: angled coronal perpendicular to the long axis of the hippocampus

  • purpose

    • detailed view of the hippocampus allowing for internal structure to be evaluated

Many/most practices will also add additional sequences, particularly SWI and DWI.

• SWI

  • sequence

    • ≤3mm (or 3D isotropic if available)

    • read more: SWI

  • planes: axial (AC-PC)

  • purpose

    • identify hemoglobin breakdown products as in post traumatic bleed and cavernomas

    • identify calcification

• DWI/ADC

  • sequence

    • 3-4 mm

    • read more: DWI

  • planes: axial (AC-PC)

  • purpose

    • may show diffusion restriction in the immediate post-ictal period or other seizure (or medication) related change e.g. CLOCCS

Additional sequences

Additional fluid sensitive sequences are also added by some to help identify areas of cortical abnormality. These can be in addition to or instead of FLAIR ⁸.

• DIR

  • sequence

    • ≤3mm (or 3D isotropic if available)

    • read more: double inversion recovery (DIR)

  • planes: axial (AC-PC) and coronal

  • purpose: similar to FLAIR, greater sensitivity to signal change

The role of post-contrast T1 sequences is usually reserved for cases where enhancing lesions are suspected either on prior imaging or on the basis of history (e.g. prior maligancny).

• T1-weighted C+

  • ​purpose: accessing tumor-like lesions, vascular malformations, or infectious disease process

When surgery is being planned, additional sequences may also be useful to minimize functional deficits.

• diffusion tensor imaging (DTI)

  • the fiber-tracking technique allow to investigate the effect of temporal lobe epilepsy on reorganization of the linguistic functions ^2,3

  • assessing for location of Meyer loop to avoid visual field defect following temporal lobectomy ⁵

• functional MRI (fMRI)

  • localize language or other functions to aid in surgical planning