Invisible Base Electrode Coordinates Approximation for Simultaneous SPECT and EEG Data Visualization

Abstract

This work was performed as part of a larger research concerning the feasibility of improving the localization of epileptic foci, as compared to the standard SPECT examination, by applying the technique of EEG mapping. The presented study extends our previous work on the development of a method for superposition of SPECT images and EEG 3D maps when these two examinations are performed simultaneously. Due to the lack of anatomical data in SPECT images it is a much more difficult task than in the case of MRI/EEG study where electrodes are visible in morphological images. Using the appropriate dose of radioisotope we mark five base electrodes to make them visible in the SPECT image and then approximate the coordinates of the remaining electrodes using properties of the 10-20 electrode placement system and the proposed nine-ellipses model. This allows computing a sequence of 3D EEG maps spanning on all electrodes. It happens, however, that not all five base electrodes can be reliably identified in SPECT data. The aim of the current study was to develop a method for determining the coordinates of base electrode(s) missing in the SPECT image. The algorithm for coordinates approximation has been developed and was tested on data collected for three subjects with all visible electrodes. To increase the accuracy of the approximation we used head surface models. Freely available model from Oostenveld research based on data from SPM package and our own model based on data from our EEG/SPECT studies were used. For data collected in four cases with one electrode not visible we compared the invisible base electrode coordinates approximation for Oostenveld and our models. The results vary depending on the missing electrode placement, but application of the realistic head model significantly increases the accuracy of the approximation.

Accuracy of the electrodes location method for simultaneous SPECT and EEG examinations

“…We performed the preliminary accuracy estimation of IM in [3] during works for improving the usefulness of the integration method in the cases where not all the marked electrodes (base electrodes) can be seen in SPECT images because of too small a dose of the radiopharmaceutical applied under the electrode. An approximation algorithm called Invisible Base Electrodes Approximation (IBEA) was developed in which electrodes averaged location on the scalp computed by Oostenveld (OOST data set) [6] was assumed as the reference data.…”

“…In previous studies, a method of marking several (the socalled base) EEG electrodes was developed, using radiopharmaceutical in order to make them visible in SPECT images [1], and afterwards -the method of determining their position in the common coordinate system for both images and reconstruction and registration of 3D images was proposed [2,3]. The method for the approximation of location of all electrodes has been developed using BioImage Suite software [4] and our own APW software [2].…”