Radiological and Clinical Value of 7T MRI for Evaluating 3T-Visible Lesions in Pharmacoresistant Focal Epilepsies

Abstract

Objective: The recent FDA approval of the first 7T MRI scanner for clinical diagnostic use in October 2017 will likely increase the utilization of 7T for epilepsy presurgical evaluation. This study aims at accessing the radiological and clinical value of 7T in patients with pharmacoresistant focal epilepsy and 3T-visible lesions.Methods: Patients with pharmacoresistant focal epilepsy were included if they had a lesion on pre-operative standard-of-care 3T MRI and also a 7T research MRI. An epilepsy protocol was used for the acquisition of the 7T MRI. Prospective visual analysis of 7T MRI was performed by an experienced board-certified neuroradiologist and communicated to the patient management team. The clinical significance of the additional 7T findings was assessed by intracranial EEG (ICEEG) ictal onset, surgical resection, post-operative seizure outcome and histopathology. A subset of lesions were demarked with arrows for subsequent, retrospective comparison between 3T and 7T by 7 neuroradiologists using a set of quantitative scales: lesion presence, conspicuity, boundary, gray-white tissue contrast, artifacts, and the most helpful sequence for diagnosis. Conger's kappa for multiple raters was performed for chance-adjusted agreement statistics.Results: A total of 47 patients were included, with the main pathology types of focal cortical dysplasia (FCD), hippocampal sclerosis, periventricular nodular heterotopia (PVNH), tumor and polymicrogyria (PMG). 7T detected additional smaller lesions in 19% (9/47) of patients, who had extensive abnormalities such as PMG and PVNH; however, these additional findings were not necessarily epileptogenic. 3T−7T comparison by the neuroradiologist team showed that lesion conspicuity and lesion boundary were significantly better at 7T (p < 0.001), particularly for FCD, PVNH and PMG. Chance-adjusted agreement was within the fair range for lesion presence, conspicuity and boundary. Gray-white contrast was significantly improved at 7T (p < 0.001). Significantly more artifacts were encountered at 7T (p < 0.001).Significance: For patients with 3T-visible lesions, 7T MRI may better elucidate the extent of multifocal abnormalities such as PVNH and PMG, providing potential targets to improve ICEEG implantation. Patients with FCD, PVNH and PMG would likely benefit the most from 7T due to improved lesion conspicuity and boundary. Pathologies in the antero–inferior temporal regions likely benefit less due to artifacts.

MRI of focal cortical dysplasia

“…While the anterior lesion was classified as FCD IIb, no FCD was diagnosed for the posterior lesion. As the patient did not get seizure-free the posterior lesionectony was extended and histology now revealed a FCD IIa Tesla MP2RAGE images have been with 3 Tesla MPRAGE images [37,38]. This comparison is biased as postprocessing using MP2RAGE images already displays FCD with larger volumes and higher z scores [34].…”

“…There is strong agreement that the visibility on MRI depends on the FCD type: FCD type II are visible on MRI provided adequate image quality on 3 Tesla machines and postprocessing is achieved. It has been reported that 7 Tesla is superior to 3 Tesla; however, post-processed 7 Tesla MP2RAGE images have been compared with 3 Tesla MPRAGE images [ 37 , 38 ]. This comparison is biased as postprocessing using MP2RAGE images already displays FCD with larger volumes and higher z scores [ 34 ].…”

“…The MP2RAGE sequence produces images with a higher B 1 homogeneity than the MPRAGE sequence and is therefore particularly suited for postprocessing [31][32][33][34][35]. The higher B 1 homogeneity is also the reason that 7 Tesla scanners are routinely equipped with this sequence [36][37][38][39][40].…”

Prognostic analysis in children with focal cortical dysplasia II undergoing epilepsy surgery: Clinical and radiological factors

“…MRI-negative is a misnomer that comprises patients without an MRI lesion or with a subtle MRI lesion but being overlooked ( 8 ). Although high-field imaging and postprocessing techniques have dramatically improved the detection rate of FCD, there are still limitations in the artifacts ( 22 ), the high false positive rate outcome ( 23 ), and clinical application promotion. Due to the preferential occurrence of dysmorphic neurons in deep cortical layers ( 24 , 25 ), MRI abnormalities are mostly displayed close to the gray matter–white matter interface.…”

Advanced neuroimaging techniques in epilepsy

“…A further systematic review gave comparable results [4]. In individuals with lesions seen at 3T, 7T imaging was associated with increased conspicuity and definition of boundaries but with increased artefacts, particularly in the temporal lobes [5], and there was benefit from postacquisition morphometric analysis in individuals with unremarkable scans at 3T [6].…”