Date Published: March 19, 2019
Publisher: Public Library of Science
Author(s): Rebecca Emily Feldman, Bradley Neil Delman, Puneet Singh Pawha, Hadrien Dyvorne, John Watson Rutland, Jiyeoun Yoo, Madeline Cara Fields, Lara Vanessa Marcuse, Priti Balchandani, Boris C. Bernhardt.
To compare by 7 Tesla (7T) magnetic resonance imaging (MRI) in patients with focal epilepsy who have non-lesional clinical MRI scans with healthy controls.
37 patients with focal epilepsy, based on clinical and electroencephalogram (EEG) data, with non-lesional MRIs at clinical field strengths and 21 healthy controls were recruited for the 7T imaging study. The MRI protocol consisted of high resolution T1-weighted, T2-weighted and susceptibility weighted imaging sequences of the entire cortex. The images were read by two neuroradiologists, who were initially blind to clinical data, and then reviewed a second time with knowledge of the seizure onset zone.
A total of 25 patients had findings with epileptogenic potential. In five patients these were definitely related to their epilepsy, confirmed through surgical intervention, in three they co-localized to the suspected seizure onset zone and likely caused the seizures. In seven patients the imaging findings co-localized to the suspected seizure onset zone but were not the definitive cause, and ten had cortical lesions with epileptogenic potential that did not localize to the suspected seizure onset zone. There were multiple other findings of uncertain significance found in both epilepsy patients and healthy controls. The susceptibility weighted imaging sequence was instrumental in guiding more targeted inspection of the other structural images and aiding in the identification of cortical lesions.
Information revealed by the improved resolution and enhanced contrast provided by 7T imaging is valuable in noninvasive identification of lesions in epilepsy patients who are non-lesional at clinical field strengths.
Approximately 20–40% of individuals with epilepsy do not respond to anti-seizure drug therapy [1–3]. For these patients, surgery may offer the best chances for seizure freedom . Magnetic resonance imaging (MRI) exams are a key element of the pre-surgical epilepsy work-up. Clear identification of lesions on an MRI exam, when concordant with electrophysiology and clinical measures, results in more accurate surgical interventions and better outcomes [5–8].
No subjects were excluded due to image quality. Final MRI observations are shown in Table 3, along with the patient age, sex and sSOZ. Examples of abnormalities detected at 7T, which were not detected at clinical field strengths, are shown in Figs 1, 2 and 3.
The high resolution and enhanced contrast afforded by imaging at 7T enabled the detection of potentially epileptogenic abnormalities (definite = 5; likely = 3; possible = 7; uncertain = 10) that were undetectable or otherwise overlooked at lower field strengths. The high resolution T2 TSE images were most frequently used for initial detection of subtle structural abnormalities at 7T. The FLAIR images were used primarily to note signal hyperintensities associated with hippocampal sclerosis. The first inversion time reconstruction of the MP2RAGE facilitated the detection of cortical lesions. The remaining MP2RAGE reconstructions and the MPRAGE images were valuable to confirm and categorize findings. Isotropic images can be re-sliced in any plane to optimize evaluation of structural asymmetries. 7T SWI allowed the effective visualization of irregular vasculature associated with cortical abnormalities, such as polymicrogyria.
The improved resolution and contrast conferred by 7T MRI revealed abnormalities of epileptogenic potential in 25 out of 37 (67% of patients) patients with focal epilepsy and who had previously non-lesional clinical MRI scans at lower field strengths. 15 of these abnormalities (40% of patients) localized to the sSOZ, and the detection of seven abnormalities (19% of patients, 28% of lesions detected) contributed directly to analysis that changed subsequent surgical intervention and treatment planning. 7T MRI also revealed several subtle structural features in both patients and controls that were undetectable at lower field strengths, with significantly more abnormalities identified in epilepsy patients. Therefore, information revealed by the 7T exams has the potential to reveal biomarkers of epilepsy, provide enhanced lesion localization of focal epilepsy, increase the success of epilepsy surgery, and advance our understanding of the etiology of the disease.