Proposal for a magnetic resonance imaging protocol for the detection of epileptogenic lesions at early outpatient stages

Purpose: Magnetic resonance imaging (MRI) is a key technology in the presurgical evaluation of patients with epilepsy. Already at early outpatient stages it can contribute to the identification of patients who are, in the case of pharmacoresistance, good candidates for epilepsy surgery. Yet, "standard head" MRI examinations often fail to displaying therapeutically relevant epileptogenic lesions. The purpose of this study is to identify an epilepsy-specific MRI protocol, which is likewise sensitive for even small epileptogenic lesions and economical enough to be applied outside specialized epilepsy centers.

Methods: Based on a large European presurgical epilepsy program comprising 2,740 patients we identified the spectrum of common epileptogenic lesions and determine the set of MRI sequences that are required for their reliable detection. Relying on a series of small, therapeutically particularly relevant lesions we determined the required slices thickness, slice angulations, and orientations for an epilepsy-specific MRI protocol.

Key findings: Indispensable for early outpatient epilepsy specific MRI are fluid attenuated inversion recovery (FLAIR), T(2) -weighted, T(1) -weighted, and hemosiderin/calcification-sensitive sequences. Slice thickness for T(2) and FLAIR must not exceed 3 mm. The T(1) image should be acquired in three-dimensional technique at 1 mm isotropic voxels size. For T(2) and FLAIR, at least two slice orientations each must be demanded in hippocampal angulation. We suggest no adaption to a clinical focus hypothesis. The resulting "essential 6" sequence protocol allows the detection of virtually all common epileptogenic lesion entities.

Significance: The creation of a broadly accepted and abundantly applied MRI protocol for epilepsy outpatients can contribute to improved and earlier identification of potential candidates for epilepsy surgery. Our systematic analysis of MRI requirements for the detection of epileptogenic lesions can serve as basis for protocol negotiations between epileptologists, radiologists, and health care funders.