Ultra-High Field 7T MRI in a Drug-Resistant Pediatric Epilepsy Cohort: Image Comparison and Radiologic Outcomes

Epileptogenic lesions in focal epilepsy can be subtle or remain undetected on conventional MRI. Ultra-high field (7T) MRI offers higher spatial resolution, contrast, and signal-to-noise ratio compared with conventional field strengths and has shown promise in adult presurgical evaluation. However, its utility in pediatric focal epilepsy, where malformations of cortical development are common, remains unclear. In this study, we directly compared 7T and 3T MRI in children with drug-resistant focal epilepsy, evaluating (1) scan tolerability, (2) image quality, and (3) lesion detection yield.

In this prospective cohort study, patients were recruited from outpatient clinics at 3 large epilepsy centers in London. Eligible participants were aged 8-17 years and had no contraindications to MRI. Scanning was conducted in 2 separate sessions at 3T and 7T. Safety and tolerability were assessed using age-specific questionnaires and analyzed using the Mann-Whitney test for differences between age groups and the McNemar χ² test for within-participant cross-field comparisons. Image quality was evaluated by a pediatric neuroradiologist and estimated quantitatively by comparing cortical thickness between field strengths. Lesion detection yield of 7T MRI was assessed by joint review with a multidisciplinary team.

A total of 63 children were assessed: 41 patients (mean age 12.6 ± 2.4 years, 22 were male) and 22 healthy controls (8-17 years, mean age 11.7 ± 2.7 years, 15 were male). Both field strengths were well tolerated, and side effects were transient. These included higher dizziness-related discomfort at 7T (p = 0.02, Cohen h = 0.89), with side effects more frequently noted in younger children (scanner noise: p = 0.02, Cohen r = -0.36; metallic taste: p = 0.02, Cohen r = -0.37). Cortical thickness was significantly thinner at 7T for both right (t = 5.65, p < 0.001, Cohen d = -0.72) and left (t = 5.01, p < 0.001, Cohen d = -0.64) hemispheres, with thinner boundaries in temporo-parietal/sensory regions. Although 7T images had increased reported inhomogeneity and artifacts, new lesions were detected in 6 of 26 patients (23%), influencing surgical management in 4 of 26 (15%) (odds ratio 1.86).

7T MRI in children with epilepsy is well tolerated and associated with a 23% improvement in lesion detection, directly affecting clinical management and surgical outcomes. Although limited by a preselected cohort with extensive diagnostic workups, our findings underscore the transformative potential of 7T MRI in presurgical planning for pediatric epilepsy.