Fetal descending aorta

Abstract

The first reports on Doppler recordings of blood velocity signals from the umbilical artery [1, 2] stimulated attempts to record blood flow in fetal vessels. In 1979 Gill presented a method combining a quasi-real-time imaging and pulsed-wave Doppler technique for estimating the volume flow in the intraabdominal part of the umbilical vein [3]. The ultrasound system used (Octoson, Ultrasonic Institute, Millers Point, Australia) did not allow the recording of high blood velocities owing to the low repetition frequency of the Doppler ultrasound pulses (2 kHz) necessitated by the long distance between the ultrasound transducers emerged in a water bath and the target vessel. Eik-Nes et al. [4] applied the principle of intermittently using two-dimensional and pulsed-wave Doppler ultrasound by combining a linear array scanner and a 2-MHz Doppler velocimeter [4]. The two transducers were mounted firmly to a unit with an inclination of the Doppler transducer of 45° to the linear array transducer. By placing the linear array transducer on the maternal abdomen so it was parallel with a sufficiently long portion of the vessel of interest, in-sonation by Doppler ultrasound under a known angle (45°) was achieved and thus the possibility of correcting the recorded mean blood velocity for the insona-tion angle (Fig. 11.1). © 2005 Springer-Verlag Berlin Heidelberg.