The transcutaneous measurement of common-carotid- artery blood flow using ultrasound

The noninvasive measurement of blood flow in an artery is important for physiological and pharmacological studies as well as in the diagnosis of disease. This paper describes the development of a noninvasive technique applicable to the carotid arteries in man, the validation of which provides a useful case study illustrating the general problems of calibrating a new noninvasive measurement. Blood flow in the human common carotid artery was calculated by combining measurements of blood velocity and arterial diameter, both of which were obtained from outside the body using ultrasound. Blood velocity was measured by recording the audio output from an ultrasonic Doppler velocimeter on magnetic tape and subsequently replaying through a zero crossing detector. Arterial diameter was measured using an ultrasonic pulse-echo A-scan instrument, modified to give two-dimensional images to aid identification of the artery. The accuracy of the measurements was studied in in-vitro and in-vivo investigations and an error in blood flow of ± 40% (± 2 sd), due mainly to error in diameter, was estimated.