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

Kowalczyk L., Goszczyńska H., Zalewska E.

Biocybernetics and Biomedical Engineering

2015

Vol. 35, no. 3

176--184

A simultaneous SPECT and EEG examination allows for a combined analysis of brain structural and functional changes. The examinations can be visualized as 3D maps of overlapping SPECT (radiopharmaceutical concentration) and EEG (bioelectric potential) data. Synchronization of both maps is difficult, as SPECT shows neither the skull outline nor the EEG electrodes. Thus a technique to reflect electrodes placement in SPECT data was needed. Earlier we devised a method to make a small number of electrodes visible in SPECT without compromising SPECT accuracy. We also proposed a procedure approximating coordinates of the 10–20 system EEG electrodes in a 3D space using only 5 electrodes coordinates, while assuming that all electrodes are placed on 9 intersecting ellipses. Here we used 20 phantoms of real heads from the BrainWeb project and the Oostenveld calculation of electrodes canonical placement in an averaged head model. We divided the electrodes placement error into an easy-to-assess ‘‘distance error’’ (distance from the head surface) and a difficult-to-assess ‘‘angular error’’ (a wrong direction in relation to the symbolic head center). Applying our procedure to the Oostenveld data set, we assessed the ratio between the distance and the angular error and showed that a majority part of the entire approximation error results from the distance error. Our approximation procedure was applied to the BrainWeb phantoms and the distance error was computed allowing estimation of the entire error of electrodes placement. The estimated average error of the electrodes coordinates' approximation procedure was 4.2 mm and the maximum error was 15.4 mm.

Integration of EEG and SPECT data acquired from simultaneous examinations

Kowalczyk M., Bajera A., Goszczynska H., Zalewska E., Krolicki L.

Biocybernetics and Biomedical Engineering

2013

Vol. 33, no. 4

196--203

The aim of this study was to develop a convenient method for superimposing SPECT images and EEG maps. This work was performed as part of research concerning feasibility of improving the localization of epileptic foci comparing to the standard SPECT examination by applying the technique of EEG mapping. The described method relies on making five EEG electrodes visible in SPECT images, calculating the coordinates of these electrodes in SPECT image space, approximating the coordinates of the remaining electrodes used in EEG recording and then computing a sequence of 3D EEG maps spanning on all the electrodes. An example of visualization of EEG and SPECT data integration was presented. The maximum error of the five base electrodes location was assessed below 10 mm. Assuming the exact placement of the base electrodes the accuracy of the proposed method was estimated below 5.5 mm.