7TMRIin focal epilepsy with unrevealing conventional field strength imaging

Abstract

SUMMARYObjective: To assess the diagnostic yield of 7T magnetic resonance imaging (MRI) in detecting and characterizing structural lesions in patients with intractable focal epilepsy and unrevealing conventional (1.5 or 3T) MRI. Methods: We conducted an observational clinical imaging study on 21 patients (17 adults and 4 children) with intractable focal epilepsy, exhibiting clinical and electroencephalographic features consistent with a single seizure-onset zone (SOZ) and unrevealing conventional MRI. Patients were enrolled at two tertiary epilepsy surgery centers and imaged at 7T, including whole brain (three-dimensional [3D] T 1 -weighted [T1W] fast-spoiled gradient echo (FSPGR), 3D susceptibility-weighted angiography [SWAN], 3D fluid-attenuated inversion recovery [FLAIR]) and targeted imaging (2D T 2 *-weighted dual-echo gradient-recalled echo [GRE] and 2D gray-white matter tissue border enhancement [TBE] fast spin echo inversion recovery [FSE-IR]). MRI studies at 1.5 or 3T deemed unrevealing at the referral center were reviewed by three experts in epilepsy imaging. Reviewers were provided information regarding the suspected localization of the SOZ. The same team subsequently reviewed 7T images. Agreement in imaging interpretation was reached through consensus-based discussions based on visual identification of structural abnormalities and their likely correlation with clinical and electrographic data. Results: 7T MRI revealed structural lesions in 6 (29%) of 21 patients. The diagnostic gain in detection was obtained using GRE and FLAIR images. Four of the six patients with abnormal 7T underwent epilepsy surgery. Histopathology revealed focal cortical dysplasia (FCD) in all. In the remaining 15 patients (71%), 7T MRI remained unrevealing; 4 of the patients underwent epilepsy surgery and histopathologic evaluation revealed gliosis. Significance: 7T MRI improves detection of epileptogenic FCD that is not visible at conventional field strengths. A dedicated protocol including whole brain FLAIR and GRE images at 7T targeted at the suspected SOZ increases the diagnostic yield.

Neuroimaging and connectomics of drug‐resistant epilepsy at multiple scales: From focal lesions to macroscale networks

“…Paralleling increases in resolution, the use of quantitative MR contrasts may better separate intracortical myelin from iron compared to “weighted” contrasts, and thus add specificity to identify typical and atypical cortical laminar architecture. Preliminary assessments suggest benefits for localization . In TLE, a recent quantitative intracortical analysis—even at conventional 3T MRI—identified intracortical anomalies suggestive of myelin alterations in hippocampal allocortices and other temporolimbic areas, suggesting coupled microstructural perturbations in mesiotemporal and adjacent paralimbic networks …”

How to choose the right MR sequence for your research question at 7 T and above?

“…7) lends itself well to revealing cortical malformation in epilepsy. In one study where various contrasts (MPRAGE, GRE, IR-FSE, ) were recorded in patients with unlocalized dysplasias at lower field, it was found that a diagnostic gain in detection was obtained using GRE and FLAIR images (De Ciantis et al, 2016). In that study, four of the six patients with abnormal 7T findings underwent epilepsy surgery.…”

Recent advances in epilepsy

“…Even in those where imaging is normal, resection on the basis of an intracranial EEG abnormality is more likely to result in seizure freedom if the resected tissue is pathologically abnormal [173]. Increasing pre-operative identification of pathology through improved MRI, through higher field strengths up to 7 T in vivo and enhancing 3 T with automated measures of hippocampal volumes potentially gives a greater chance of identifying candidates who may benefit from surgery [174–176]. In those whom structural imaging remains negative, then FDG-PET can aid in the decision making, either in favour of surgery, e.g.…”