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The Magstim Rapid uses a pneumatic foot pedal that connects to the coil control
box to prevent accidental discharges (Fig. 4). This foot pedal has to be depressed in
order for the TMS system to trigger, which is not practical for computer control.
Therefore a new coil control box was built which adapted the circuitry for the foot pedal
to use a large button instead (Fig. 5). When struck, the button halts the system in the
same way that taking your foot off of the pneumatic pedal would with the old coil
control box. This feature is necessary in order to provide a quick way to end TMS
stimulation in the event that a subject has a seizure, which is a possibility although very
unlikely unless the subject is epileptic or very high stimulation frequencies are used.
Next to the switch is an LED that is used to indicate whether or not the system is
halted by the emergency switch. The new coil control box also has a button to switch
between manual and computer control. This switch is connected to pin 1 of the TMS
console's centronic port (Table 1), and when depressed signals the Magstim Rapid to
ignore the front panel button interface and instead respond to computer control. This
switch allows the TMS system to be easily converted for use inside or outside the
scanner.
Besides these features, the new coil control box also contains additional circuitry
for noise elimination, which is described in the next section. ʌ