Home Button One Button Two Button Three Button Four

MEG/EEG

PET

Image Analysis

Optical Imaging

BrainStorm

BrainSuite

Aspire

Digimouse

MEG/EEG

PET

Image Analysis

Misc Topics

Group Members

MEG & EEG » Phantom Warping

 

Multichannel electroencephalography (EEG), as compared to magnetoencephalography (MEG) or functional magnetic resonance imaging (fMRI), is a widely available and inexpensive method for measuring functional information about the human brain. Ideally, individual anatomical MR scans of the subject are used, both for defining the forward model that relates source location and strength to the measured scalp potentials, and for visualizing and analyzing the estimated sources with respect to the cortical anatomy of the subject. In practice, EEG studies are often performed without accompanying anatomical scans. To overcome this problem we propose a stereotactic atlas-based procedure in which surface landmarks are used to warp an atlas to the subject’s scalp morphology. The warped atlas is used to define a forward model for source localization. In this way, we can infer the approximate locations in cortical anatomy of EEG sources without access to an individual’s MR image.

Figure: Scalp, outer skull, inner skull, and white matter cortical surface of the Montreal brain phantom, used as an atlas. These surfaces, together with the phantom MR scan, are warped into an individual subject's space.

 

Registration between a subject and the atlas (Montreal brain phantom) can be based on matching of landmarks, surfaces or image intensity within the brain. The approach we follow is somewhat different because the features that are used for registration of a subject and atlas are external (cranial and electrode locations) rather than intracranial. While we would expect better registration using brain landmarks, these are not available to us. The phantom electrodes are based on an extention of the 10-20 system with placement determined by the locations of the nasion, inion and left and right preauricular points.

The phantom is warped into the subject space using thin place splines.

 

VIDEO AVAILABLEVIDEO AVAILABLEVIDEO AVAILABLE

Figure: Left: The subject's electrode locations overlap with the phantom's scalp and brain surfaces; Middle: The phantom electrodes (red) are assigned to proper subject electrodes (yellow) based on the 10-20 system or, alternatively, euclidean distances; Right: The warped phantom surfaces match the subject electrode locations. Click on the images to watch video.

 

The phantom warping procedure in now available on BrainStorm