7T MRI Adds Critical Information for Epilepsy Presurgical Evaluation

In the largest study to date assessing the value of in vivo structural 7-tesla (7T) MRI for epilepsy presurgical evaluation, 7T MRI revealed subtle focal cortical dysplasia in about half of patients who had no lesions detected by 3T MRI; moreover, complete resection of these lesions was significantly associated with postoperative seizure freedom. The study’s findings were reported in a Dec. 7 platform presentation at the American Epilepsy Society’s 2019 annual meeting.

“Information gleaned from the superior resolution of 7T MRI can lead to better outcomes in patients with focal epilepsy who do not have apparent lesions seen on 3T MRI,” says lead author and Cleveland Clinic Epilepsy Center staff scientist Irene Wang, PhD, who presented the study results.

Background: Evaluating a new technology

Although 7T MRI was first approved by the FDA for clinical diagnostic use in October 2017, Cleveland Clinic had used its 7T MRI system for research purposes starting in 2014. 7T field strength offers increased signal-to-noise and contrast-to-noise ratios, resulting in sharper images with potentially better detection and visualization of cortical malformations.

“Because of the expense of 7T MRI scanners and the short time they have been used clinically, data assessing their utility are especially important,” Dr. Wang observes.

Study design and results

To that end, between 2014 and 2018 Dr. Wang and colleagues prospectively selected 100 patients with focal drug-resistant epilepsy seen at Cleveland Clinic to undergo 7T MRI. All were also assessed with 3T MRI.

Post-processing of the 7T T1-weighted MP2RAGE sequence was done using the morphometric analysis program (MAP), with images compared to a database of 7T MRI images obtained from 50 healthy controls. In addition to studying 7T MRI in the largest cohort of epilepsy patients to date, this investigation represents the first report of MAP post-processing of images from a 7T MRI scanner (more information on MAP can be found here).

7T images were reviewed by an experienced board-certified neuroradiologist, and the clinical significance of 7T findings was evaluated in terms of overlap with ictal onset as indicated by intracranial EEG (ICEEG) as well as surgical findings, postoperative seizure outcomes and histopathology.

Key findings included the following:

• 7T MRI detected lesions not visible on 3T MRI. Of the study’s 100 patients, 53 had no lesions detected by 3T MRI (see Figure 1 for an example). In nearly half of this group (26 patients, 49%), lesions were identified by 7T MRI.
• MAP post-processing yielded more than visual analysis alone. Of the lesions identified by 7T MRI that were not visible by 3T MRI, 12 were visible with unaided 7T MRI and 22 were detected with MAP guidance.
• New 7T-identified lesions were clinically significant. In 87% of those who underwent ICEEG (13/15), the 7T-detected lesion location was identical to or contained within the ICEEG ictal onset. In addition, complete resection of 7T-identified lesions was significantly associated with seizure freedom at 12 months (P = 0.03). Histopathology of resected lesions mainly revealed focal cortical dysplasia.
• 7T MRI enhanced delineation of 3T MRI-detected lesions. Additional small ipsilateral or contralateral lesions were found by 7T MRI in 9 of 47 patients (19%) who had lesions apparent on 3T MRI; most of these patients had polymicrogyria/nodular heterotopia malformations. However, not all lesions detected were epileptogenic.

Dr. Wang expects the full study results to be published in 2020.

Figure 1. 7T images from a patient whose 3T MRI revealed no epileptogenic lesion. With the increased signal-to-noise and contrast-to-noise ratios of 7T, small focal cortical dysplasia with thickened cortex was seen at the depth of the right parieto-occipital sulcus (arrows). Detection of this lesion played a crucial role in the patient’s presurgical evaluation.

Takeaways and future efforts

According to Dr. Wang, the Cleveland Clinic experience demonstrates that 7T MRI can play an important role in epilepsy presurgical evaluation.

“Findings from 7T MRI and MAP guidance, when consistent with a patient’s electro-clinical profile, should be incorporated into plans for ICEEG implantation and resective or ablative surgery,” concludes Dr. Wang. “7T MRI could particularly benefit patients with drug-resistant epilepsy without lesional findings on 3T MRI.”

She adds that the Cleveland Clinic team will next be focusing on making 7T sequences more efficient in order to reduce scan time. The team also intends to better adapt MRI post-processing techniques to 7T images in order to further increase the yield for detection of focal cortical dysplasia.