A device for guiding a medical instrument is described, which comprises a guide tube, which has a longitudinal opening extending substantially from a distal end to a proximal end of the guide tube, wherein the guide tube comprises a rounded bottom and two parallel side walls so that the guide tube is about semi-circular in cross section. The drain current of the memory cell is read when the gate voltage is at a first predetermined voltage, and if the read drain current is greater than a predetermined current level, then a hard breakdown is detected. In a preferred embodiment, the persistence actuator disables persistence filtering in response to contrast agent destructive ultrasonic transmissions. In a third embodiment, content is distributed on demand after the publication time by a media distribution server. The touch panel controller acts to control and interpret the touch panel. A power status of each node is indicated utilizing one of the first level of power indicators.