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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.

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Preliminary results of research to devise a method allowing spatial alignment of BEAM maps obtained from EEG examinations with SPECT data are presented. The main concept of the method presented lies in simultaneous recording of multi-channel EEGs during SPECT examination, and also in visualizing location of EEG electrodes on SPECT images that provide spatial three dimensional coordinates assignment. The proposed methodology of simultaneous SPECT and EEG examinations could be a significant complement to results of epileptic focus localisation obtained with the ISAS method used for the last few years. The ISAS method allows localisation of focuses with 80% confidence, but it requires carrying out MRI examinations for alignment of compared anatomical structures on two SPECT images. Complementing these results with a BEAM map analysis would improve significantly the effectiveness of the examinations. This work presents results of experiments carried out on the Jaszczak phantom.