Comparison showing 3T and 7T scans for the same participant. Credit: P Simon Jones, University of Cambridge.
A University of Cambridge team has used powerful new MRI scans to enable life-changing surgery in a first for adults with epilepsy.
A new technique has enabled ultra-powerful magnetic resonance imaging (MRI) scanners to identify tiny differences in patients’ brains that cause treatment-resistant epilepsy.
In the first study to use this approach, it has allowed doctors at Addenbrooke’s Hospital, Cambridge, to offer the patients 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.
But in a new study, researchers in Cambridge and Paris have used a technique that overcomes this problem.
Focal epilepsy
Around 360,000 people in the UK have a condition known as focal epilepsy, which causes seizures to spread from part of the brain.
A third of these individuals have persistent seizures despite medication, and the only treatment that can cure their condition is surgery.
Epileptic seizures are the sixth most common reason for hospital admission.
In order for surgeons to perform this operation, they need to be able to see the lesions (diseased tissue) in the brain responsible for the seizures.
Then, they can work out exactly which areas to remove to cure the patient’s epilepsy.
If surgeons are able to see the lesions on MRI scans, this can double the chances of the patient being free of seizures following surgery.
Ultra-high field 7T MRI scanners allow much more detailed resolution on brain scans and have been shown in other countries to be better than the NHS’s best 3T MRI scanners at detecting these lesions in patients with drug-resistant epilepsy (and in fact, most NHS hospitals have even weaker, 1.5T scanners).
However, 7T MRI scans are susceptible to dark patches known as signal dropouts. These dropouts commonly occur in the temporal lobes, where most cases of epilepsy arise.
To overcome this problem, researchers at the University of Cambridge’s Wolfson Brain Imaging Centre, working with colleagues at the Université Paris-Saclay, trialled a technique known as ‘parallel transmit’, which uses eight transmitters around the brain rather than just one to avoid the 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 Paris group’s plug-and-play sequences avoid the need to calibrate the scanner at every visit, making it practical to use these scans for scanning patients.”
Confirmation
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.
They found that the parallel transmit 7T scanner identified previously unseen structural lesions in nine patients.
It confirmed in four patients suspected lesions detected using 3T scanners, and in a further four patients showed that suspected lesions could be disregarded.
Parallel transmit 7T images were clearer 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.
Epilepsy management
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 that surgery was no longer an option.
Five patients, because of the size or location of their lesions, 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, and the 7T scans allowed it to be offered to the patients it was most likely to help.
Dr Thomas Cope from the University’s Department of Clinical Neurosciences, and a Consultant Neurologist at CUH, said: “Having epilepsy that doesn’t respond to anti-seizure medications can have a huge impact on patients’ lives, often affecting their independence and their ability to maintain a job.
“We know we can cure many of these patients, but that requires us to be able to pinpoint exactly where in the brain is the root of their seizures.
“7T scanners have shown promise over the past few years since their introduction, and now, thanks to this new technique, more epilepsy patients will be eligible for life-changing surgery.”
When the team asked patients about their experience afterwards, the patients reported only minor and occasional negative experiences, such as dizziness on scanner entry and additional claustrophobia from the head coil.
This suggests that parallel transmit 7T MRI is acceptable to patients.
The study is published in Epilepsia.
