Scientists have employed a novel technique that allows ultra-powerful MRI scanners to identify subtle differences in patients’ brains that contribute to treatment-resistant epilepsy.
The first study utilising this approach enabled doctors at Addenbrooke’s Hospital in Cambridge to provide patients with surgery to cure their condition.
Previously, 7T MRI scanners – so called because they operate using a 7 Tesla magnetic field, more than double the strength of previous 3T scanners – have suffered from signal blackspots in crucial parts of the brain.
However, in research published in Epilepsia, researchers in Cambridge and Paris have used a technique to overcome this problem.
Approximately 360,000 people in the UK have a condition known as focal epilepsy, which causes seizures to spread from one part of the brain.
One-third of these individuals experience persistent seizures despite medication, and the only treatment that can cure their condition is surgery. Epileptic seizures are the sixth most common cause of hospital admission.
Surgeons need to visualise the lesions in the brain that are responsible for the seizures to perform this operation. Then, they can determine precisely which areas to remove to cure the patient’s epilepsy.
If surgeons can detect the lesions on MRI scans, this can double the chances of the patient being seizure-free following surgery.
Ultra-high-field 7T MRI scanners offer significantly better resolution for brain scans and have demonstrated, in other countries, superior performance compared to the NHS’s top 3T MRI scanners in detecting lesions in patients with drug-resistant epilepsy.
However, 7T MRI scans are prone to dark patches known as signal dropouts, which commonly occur in the temporal lobes, where most cases of epilepsy originate.
To address this issue, researchers at the University of Cambridge’s Wolfson Brain Imaging Centre, in collaboration with colleagues from Université Paris-Saclay, tested a ‘parallel transmit’ technique.
This method uses eight transmitters around the brain instead of just one to prevent problematic drop-outs.
Chris Rodgers, Professor of Biomedical Imaging at the University of Cambridge, said: ‘It used to be the case that MRI scanners used a single radio transmitter, but in a similar way to how single wifi routers leave areas where you will struggle to get a signal, so these scanners would tend to leave blackspots on brain scans where it was hard to make out the relevant tissue.
‘Now, by using multiple radio transmitters positioned around the patients’ head – like having a wifi mesh around your home – we can get much clearer images with fewer blackspots. This is important for the epilepsy scans because we need to see very precisely which part of the brain is misbehaving.’
The team tested their approach with 31 drug-resistant epilepsy patients recruited at Addenbrooke’s Hospital, part of Cambridge University Hospitals NHS Foundation Trust (CUH), to see if the parallel transmit 7T scanner was better than conventional 3T scanners at detecting brain lesions.
The parallel transmit 7T scanner identified unseen structural lesions in nine patients. It confirmed suspected lesions detected using 3T scanners in four patients and showed that suspected lesions could be disregarded in four more patients.
Parallel transmit 7T images were more explicit than conventional (‘single transmit’) 7T images in more than half of the cases (57%), and in the remaining cases, the images were equally clear. Single-transmit scanners never outperformed parallel-transmit scanners.
As a result of their findings, more than half of the patients (18 patients, or 58%) had the management of their epilepsy changed.
Nine patients were offered surgery to remove the lesion, and one patient was offered laser interstitial thermal therapy (which uses heat to remove the lesion).
For three patients, scans showed more complex lesions, meaning surgery was no longer an option.
Because of the size or location of their lesions, five patients were offered stereotactic electroencephalography (sEEG), a technique for pinpointing the lesions using electrodes inserted into the brain. This procedure is not used for everyone because it is very costly and invasive, but the 7T scans allowed it to be offered to the patients it was most likely to help.
When the team asked patients about their experiences afterwards, they reported only minor and occasional adverse incidents, such as dizziness upon entering the scanner and increased claustrophobia from the head coil. This suggests that parallel transmit 7T MRI is acceptable to patients.
The research is published in Epilepsia.
