*2.3. CT*/*MRI Comparison*

In order to validate the use of CT imaging compared to the standard MRI imaging, we compared the e-field calculated by the system in both modalities in four sets of imaging data. For each head model, 26 stimulation targets were put on the cortical surface, distributed around the central sulcus (Figure 1C). The virtual model was co-registered to a dummy head in 3 cases and to the actual patient in 1 case. Each target was subsequently stimulated with an intensity of 30% of maximum stimulator output and the calculated local maximum e-field was recorded. This specific stimulation intensity was selected since 30% of maximum stimulator output is a common benchmark for motor thresholds in neurosurgical motor mappings.
