[Homer-users] SDgui - SD file creation

[Nagels-Coune, Laurien (Stud. FPN)]

Dear all,

I collected some pilot data with a NIRx machine and want to use the NIRx2nirs matlab script by Rob Cooper to analyze my data in Homer2. I created an SD file in Homer2 but have a few questions concerning this file:

I understand that I have to maintain the real-world NIRx source and detector numbers in the SD file but what about the optode distances? The X and Y axes are in cm but placing optodes in this grid feel so arbitrary. I found this piece of text in the Homer2 manual: " Dimensions are relative coordinates (i.e. to some aribitrary defined zero point).  Although the probe dimensions can be three dimensional, display and image reconstructions are currently only allowed in two dimensional (i.e. z=constant). " 

I placed the optodes on the head according to the 10-20 system but I am not sure how to relate this to the 100 by 100 cm grid. I guess I am afraid that the probe geometry will influence the creation of the .nirs file (optode distance is incorporated in the Beer-Lambert law and will therefore influence my oxy and deoxy levels). Or, is the SD file only employed for visualization purposes?

Kind regards,
Laurien
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