An image forming apparatus comprises an image sensor configured to extend in a horizontal scanning direction, a carriage, a guide section and a reading control section. The apparatus comprises a processing chamber and a holder for securing the workpiece within the processing chamber so that a substantial portion of the top face and a substantial portion of the bottom face is exposed to a processing material introduced into the processing chamber. First and second contacts are provided in two diagonally opposed corner portions of the sensor. Further, it may be used to selectively tap off a portion of the optical signal, for example to read header information in a data stream which indicates the destination switch port of the optical data, without disrupting the remaining optical data. The stimulation lead introducer may enter the epidural region proximate a spine of a patient via a guidewire.