Extravasation detector

Ultrasound Doppler probe 2 is placed above the vein downstream of a contrast medium infusion site and measures the flow velocity in the vein. Processor 4 converts the output from the probe 2 into a form that may be displayed as an image on display unit 5. It also determines whether the velocity corresponds to a flow of contrast medium along the vein. If the cannula 13 is properly sited and the contrast medium as desired along the vein, this will lead to an increased flow velocity in the vein. This is detected by ultrasound probe 2 and the processor 4 will determine that no extravasation has occurred. However, where extravasation of contrast medium occurs a low or zero output from probe 2 will result and processor 4 determines that extravasation has occurred, and it immediately sends a "stop" signal, e.g. an alarm, to pump controller 11 which stops pump 10.