A method and apparatus are provided for use in locating a target region which is situated in the body of a subject, for example for the delivery of drugs. The system includes an assembly for controlling the flow of fluid from a fluid reservoir to a conduit, such as a needle. A sensor detects a characteristic indicative of the fluid pressure in the conduit. The system processes data from the sensor to detect the presence of a pulsatile waveform. A controller may control further operation of the system based on information regarding the presence of the pulsatile waveform and features of the waveform, such as amplitude.
