Monitoring X-ray contrast agent injections with Doppler ultrasound

During CT examinations, approximately 100 ml of X-ray contrast agent is regularly injected intravenously. In some rare cases, some or all the contrast agent may leak out of the vein and into the surrounding tissue, causing an extravasation. In other cases, equipment failure may prevent the contrast agent from being injected. This paper presents an ultrasound unit made for monitoring contrast agent injections during CT investigations. The unit uses a specially designed transducer attached to the arm of the patient, and a three-channel CW Doppler unit monitors the contrast agent injection continuously. The system has been tested on 198 patients in various CT centers. The preliminary results show that a correct injection is recognized by a strong increase in Doppler signal strength and velocity. Four cases of extravasations and equipment failure were detected as either delayed or missing increase in Doppler power.