High-Field 7T MRI in a drug-resistant paediatric epilepsy cohort: image comparison and radiological outcomes

Background and Objectives: Epileptogenic lesions in focal epilepsy can be subtle or undetected on conventional brain MRI. Ultra-high field (7T) MRI offers higher spatial resolution, contrast and signal-to-noise ratio compared to conventional imaging systems and has shown promise in the pre-surgical evaluation of adult focal epilepsy. However, the utility of ultra-high field MRI in paediatric focal epilepsy, where malformations of cortical development are more common, is unclear. This study compared 7T to conventional 3T MRI in children with epilepsy by comparing: (i) scan tolerability; (ii) radiological image quality; (iii) lesion yield. Materials and Methods: Children with drug-resistant focal epilepsy and healthy controls were recruited prospectively and imaged at both 3T and 7T. Safety and tolerability during scanning was assessed via a questionnaire. Image quality was evaluated by an expert paediatric neuroradiologist and estimated quantitatively by comparing cortical thickness between field strengths. To assess lesion detection yield of 7T MRI, a multi-disciplinary team jointly reviewed patients' images. Results: 41 patients (8-17 years, mean=12.6 years, 22 male) and 22 healthy controls (8-17 years, mean=11.7 years, 15 male) were recruited. All children completed the scan, with no significant adverse events. Higher discomfort due to dizziness was reported at 7T (p=0.02), with side-effects more frequently noted in younger children (p=0.02). However, both field strengths were generally well-tolerated and side-effects were transient. 7T images had increased inhomogeneity and artefacts compared to those obtained at 3T. Cortical thickness measurements were significantly thinner at 7T (p<0.001). 8/26 (31%) patients had new lesions identified at 7T which were not identified at 3T, influencing the surgical management in 4/26 (15%). Discussion: 7T MRI in children with epilepsy is feasible, well-tolerated and is associated with a 31% improvement in lesion detection rates.