Better localisation for epilepsy surgery by optimising simultaneous EEG and functional MRI recordings at 7T
Lead Research Organisation:
King's College London
Department Name: Imaging & Biomedical Engineering
Abstract
For adults and children with focal epilepsy, surgical removal of the brain region responsible for seizure generation is the only possible complete cure. This can remove dependence on medication, and dramatically improve quality of life. Surgical success relies on accurate localisation of the generators of epileptic activity via imaging techniques such as MRI and electroencephalography (EEG). These two key modalities can be combined; epileptic activity measured in EEG is used as a model of expected changes in functional MRI timeseries. This provides a high spatial resolution map showing the areas with signal
changes associated with the epileptic activity that has been shown to be a useful localisation method [1].
However, EEG-fMRI is limited by fMRI sensitivity that typically measures signal changes of 1-2%. Ultra-high field 7T MRI offers a solution because fMRI signal changes are substantially increased to 5-10% and this could dramatically improve the technique's sensitivity and spatial specificity. However, simultaneous EEG-fMRI at 7T is a significant technical challenge [2]. This project will design and test EEG configurations for use at 7T so it can be used in patient populations. This will include investigating tissue heating and EEG system design solutions to mitigate this risk. Further, the impact of each modality on the other in terms of data quality will be characterised and the EEG system hardware configuration redesigned to optimise signal quality. This may also encompass potential algorithmic development to improve image quality, including AI methods to improve upon current denoising approaches. Having optimised 7T EEG-fMRI an initial pilot investigation of its utility in epilepsy is envisaged.
Aim of the investigation (up to 150 words): This project will design and test EEG configurations for use at 7T so it can be used in patient populations. This will include investigating tissue heating and EEG system design solutions to mitigate this risk. Further, the impact of each modality on the other in terms of data quality will be characterised and the EEG system hardware configuration redesigned to optimise signal quality. This may also encompass potential algorithmic development to improve image quality, including AI methods to improve upon current denoising approaches. Having optimised 7T EEG-fMRI an initial pilot investigation of its utility in epilepsy is
envisaged.
Objective 1: Determine safety limits for operation of new 7T compatible EEG system
We will test and optimise custom configured EEG system designs with the project partner Brain Products. This will involve thermometry and thermal imaging testing in phantoms and human subjects. Simulation using in-silico models using the electromagnetic field (EM) simulation software package Sim4life may also be involved informed by the results of initial experimental testing. Different cable routings and the size and distribution of impedance within the wires will be tested. One of the main limitations of new high field 7T scanners is the high spatial variability in the RF transmit field (B1+) owing to the shorter
wavelength required that increases tissue interactions. Reductions to the B1+ field can be seen in the figure c below from initial testing with associated imaging artefacts in figure b. One important method for mitigating this is transmit RF coils that provide different fields from multiple coil elements that, when optimally combined, reduce B1 field variability and could be used to reduce interactions with the EEG cap. This testing will therefore be performed for both single and parallel transmit MRI coils, and modes of operation that limit EEG interactions explored.
Months 1-6, heating risk assessment and reduction. Months 4-12 exploration of risk reduction using parallel transmit modes of operation.
Objective 2: Characterise and mitigate artefacts for new 7T compatible EEG systems at 7T. & Objective 3: MRI Protocol development and data assessme
changes associated with the epileptic activity that has been shown to be a useful localisation method [1].
However, EEG-fMRI is limited by fMRI sensitivity that typically measures signal changes of 1-2%. Ultra-high field 7T MRI offers a solution because fMRI signal changes are substantially increased to 5-10% and this could dramatically improve the technique's sensitivity and spatial specificity. However, simultaneous EEG-fMRI at 7T is a significant technical challenge [2]. This project will design and test EEG configurations for use at 7T so it can be used in patient populations. This will include investigating tissue heating and EEG system design solutions to mitigate this risk. Further, the impact of each modality on the other in terms of data quality will be characterised and the EEG system hardware configuration redesigned to optimise signal quality. This may also encompass potential algorithmic development to improve image quality, including AI methods to improve upon current denoising approaches. Having optimised 7T EEG-fMRI an initial pilot investigation of its utility in epilepsy is envisaged.
Aim of the investigation (up to 150 words): This project will design and test EEG configurations for use at 7T so it can be used in patient populations. This will include investigating tissue heating and EEG system design solutions to mitigate this risk. Further, the impact of each modality on the other in terms of data quality will be characterised and the EEG system hardware configuration redesigned to optimise signal quality. This may also encompass potential algorithmic development to improve image quality, including AI methods to improve upon current denoising approaches. Having optimised 7T EEG-fMRI an initial pilot investigation of its utility in epilepsy is
envisaged.
Objective 1: Determine safety limits for operation of new 7T compatible EEG system
We will test and optimise custom configured EEG system designs with the project partner Brain Products. This will involve thermometry and thermal imaging testing in phantoms and human subjects. Simulation using in-silico models using the electromagnetic field (EM) simulation software package Sim4life may also be involved informed by the results of initial experimental testing. Different cable routings and the size and distribution of impedance within the wires will be tested. One of the main limitations of new high field 7T scanners is the high spatial variability in the RF transmit field (B1+) owing to the shorter
wavelength required that increases tissue interactions. Reductions to the B1+ field can be seen in the figure c below from initial testing with associated imaging artefacts in figure b. One important method for mitigating this is transmit RF coils that provide different fields from multiple coil elements that, when optimally combined, reduce B1 field variability and could be used to reduce interactions with the EEG cap. This testing will therefore be performed for both single and parallel transmit MRI coils, and modes of operation that limit EEG interactions explored.
Months 1-6, heating risk assessment and reduction. Months 4-12 exploration of risk reduction using parallel transmit modes of operation.
Objective 2: Characterise and mitigate artefacts for new 7T compatible EEG systems at 7T. & Objective 3: MRI Protocol development and data assessme
People |
ORCID iD |
| David Carmichael (Primary Supervisor) | |
| Rebecca Meagher (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| MR/W006820/1 | 01/10/2022 | 30/09/2028 | |||
| 2886505 | Studentship | MR/W006820/1 | 01/10/2023 | 30/09/2027 | Rebecca Meagher |