A technique is described, using the UI Octoson and a frequency-offset pulsed Doppler system, to obtain fully quantitative blood flow measurements in deep-lying vessels. By uniformly insonating the vessel and using a mean frequency Doppler demodulator, average velocity is obtained regardless of the velocity profile. B -scan imaging provides the necessary anatomic information to calculate volume flow from this average velocity. Results of in vitro flow measurement tests indicate accuracies of ± 14% rms error, ± 32% maximum error. The causes of error appear to be well understood, and in a number of cases they can be corrected. Preliminary clinical measurements of fetal umbilical vein flow and adult right branch portal vein flow are also presented.

Pulsed Doppler with B-mode imaging for quantitative blood flow measurement.

Elastography can produce quality strain images in vitro and in vivo. Standard elastography uses a coherent cross-correlation technique to estimate tissue displacement and tissue strain using a subsequent gradient operator. While coherent estimation methods generally have the advantage of being highly accurate and precise, even relatively small undesired motions are likely to cause enough signal decorrelation to produce significant degradation of the elastogram. For elastography to become more universally practical in such applications as hand-held, intravascular and abdominal imaging, the limitations associated with coherent strain estimation methods that require tissue and system stability, must be overcome. In this paper, we propose the use of a spectral shift method that uses a centroid shift estimate (Fig. 5) to measure local strain directly. Furthermore, we also show theoretically that a spectral bandwidth method can also provide a direct strain estimation. We demonstrate that strain estimation using the spectral shift technique is moderately less precise but far more robust than the cross-correlation method. A theoretical analysis as well as simulations and experimental results are used to illustrate the properties associated with this method.

Power spectral strain estimators in elastography

Five different methods of obtaining directional information from Doppler Velocimeters are discussed, with comments on their relative applicability. These are based on the techniques of Single Sideband, Heterodyne, and Phase Quadrature detection. Real-time spectrum analysis of these Doppler signals and display of their waveform shapes is also considered. Some examples of directional waveforms taken from human subjects are shown and system configurations, suitable for clinical measurement, are outlined.

Directional Doppler techniques for detection of blood velocities.

The mean frequency Doppler demodulator is of interest for quantitative measurement of blood flow, particularly in small or deep-lying vessels. It is thus desirable that the various potential sources of error be considered, and that their effects on its performance be quantified where possible. This paper analyzes the effects of interfering noise, more than one vessel falling within the Doppler sample volume, Doppler filtering, frequency aliasing, and double-sidebanding of the Doppler signal. The analysis applies to either frequency offset or non-offset Doppler systems, and a variety of blood velocity distributions is considered. It is shown that, in a number of instances, the errors can be predicted and therefore corrected. Experimental results are presented confirming the theoretical analysis.

Performance of the mean frequency Doppler modulator.

Practical aspects of a method for estimating the mean velocity waveform for a CW ultrasound system are described. The method, based on the technique proposed by Gerzberg and Meindl (1977), generates an analog mean signal for both forward and reverse flow with an accuracy of better than ± 5%. Application of the circuit for arterial assessment are presented, and its potential use for determining carotid spectral broadening is considered.

H. Thön

Papers

A directional quantifying Doppler system for measurement of transport velocity of blood.