Subtraction procedure for the registration of tissue perfusion with Doppler ultrasound.

Tissue perfusion, i.e., in muscles or parenchymatous organs, is of both physiological and pathophysiological interest. The measurement of tissue perfusion is an unsolved problem. The Doppler ultrasound method is well suited to this purpose. However, measurements using this technique may be disturbed by movements or vibrations such as heart motion, muscle trembling or vibration of the subsoil (i.e. the examination table). These interfering movements produce Doppler frequencies in the same frequency range as slowly flowing erythrocytes, causing artifacts to appear in the measured data. The goal of this project was to suppress such artifacts with the help of a subtraction procedure. The mathematical theory of this subtraction procedure and its implementation in a newly developed two channel Doppler system are presented. This system was successfully tested on a phantom which is able to generate flow and movement artifacts. Preliminary measurements in the forearms of volunteers showed that movement artifacts can be at least partially suppressed.

Human abdominal aorta: comparative measurements of blood flow with MR imaging and multigated Doppler US.

Magnetic resonance (MR) imaging has proved to be a new alternative method for the noninvasive detection and quantification of blood flow in human vessels. By means of standard gradient echo sequences triggered with electrocardiography on a 1.5-T whole-body imaging system, the authors measured the flow-induced phase shift in the abdominal aorta of healthy volunteers. The instantaneous two-dimensional velocity profiles and the integrated flow rate were determined in intervals down to 21 msec throughout the cardiac cycle. The results were validated by means of comparative measurements with a multigated Doppler ultrasound instrument. The velocity values acquired with this instrument in one spatial dimension in the anteroposterior direction of the abdominal aorta agreed to a great extent with the temporal and spatial corresponding values recorded with MR imaging. The same high correlation between the two methods was found for the calculated instantaneous total blood flow.