Assessment of propagation velocity by contrast echocardiography for standardization of color Doppler propagation velocity measurements

BACKGROUND: Color Doppler propagation velocity (Vp) (color-Vp) has not yet been standardized, although it should be able to specifically reflect the intraventricular movements of left ventricular (LV) inflow. Because contrast echocardiography can depict a specified flow, we used this modality to standardize measurements of color-Vp of LV inflow. METHODS: We performed contrast echocardiographic examinations in 100 patients (70 men, 30 women; age 53 +/- 12 years). Four types of color-Vp were measured: by the flow wave front method and by aliasing method using 3 aliasing velocity levels based on the peak velocity of early diastolic flow of transmitral flow. We also determined contrast echocardiographic Vp by M-mode imaging of LV inflow (contrast-Vp). RESULTS: Contrast-Vp and all 4 types of color-Vp could be compared in 86 patients. Contrast-Vp was significantly lower than color-Vp ( P < .01), except for color-Vp measured at the aliasing level 50% > peak velocity of early diastolic flow >/= 40% (color-Vp 40). A close relationship was observed between contrast-Vp and color-Vp 40 ( r = 0.801, P < .0001). Contrast-Vp and color-Vp 40 showed high ability to detect abnormal transmitral flow patterns according to receiver operating characteristics curves (area under curve for contrast-Vp, 0.94; for color-Vp 40, 0.90). CONCLUSIONS: Our results should be useful in standardization of color-Vp measurement to specifically reflect propagation of the fluid elements derived from LV inflow, with ability to distinguish LV filling abnormalities.     

Cross-beam vector Doppler ultrasound for angle-independent velocity measurements

Combining Doppler measurements taken along multiple intersecting ultrasound (US) beams is one approach to obtaining angle-independent velocity. Over 30 laboratories and companies have developed such cross-beam systems since the 1970s. Early designs focused on multiple single-element probes. In the late 1980s, combining multiple color Doppler images acquired from linear-array transducers became a popular modality. This was further expanded to include beam steering and the use of subapertures. Often, with each change in design, came a new twist to calculating the velocity. This article presents a review of most proposed cross-beam systems published to date. The emphasis is on the basic design, the approach used to determine the angle-independent velocity, the advantages of the design, and the disadvantages of the design. From this, requirements needed to convert the idea of angle-independent vector Doppler into a commercial system are suggested.     

Fetal iliac angle measurements by three-dimensional sonography.

OBJECTIVE: To determine the technical reliability of fetal iliac angle measurements by three-dimensional sonography as a prenatal marker for Down syndrome. METHODS: Three-dimensional multiplanar views of the fetal pelvis were used to standardize iliac angle measurements from 35 normal second-trimester pregnancies. Measurement reliability for a single examiner and between two different examiners were analyzed by intraclass correlation. Normal iliac angle measurements were compared to those obtained from 16 fetuses with trisomy 21. RESULTS: The mean axial angle for normal fetuses was 79 +/- 5.5 degrees, which was significantly less than that observed in fetuses with trisomy 21 (87.7 +/- 4.9 degrees ) (P < 0.001). Iliac angles did not correlate with gestational age. Axial angles were reproducible between two examiners who measured the same multiplanar view of the pelvis. Inter- and intraobserver reliability were also acceptable after a standardized multiplanar view was independently obtained by each examiner (intraclass correlation = 0.91 for both). Coronal angles were unreliable because of difficulties with finding a reproducible measurement plane. For a false-positive rate of 5%, an axial angle threshold of 87 degrees correctly identified 56% of fetuses with trisomy 21. CONCLUSION: Axial iliac angle measurements are reliable by standardized three-dimensional multiplanar views of the pelvis and can be used to identify some fetuses at increased risk for trisomy 21.     

The effect of echo contrast agent on Doppler velocity measurements

The purpose of this investigation was to determine the effect of echo contrast agents on spectral Doppler velocity measurements. SH U 508A was administered by IV injection in 15 patients. The transmitral flow velocity was measured at the E- and A-wave peaks before the start and at the peak of the contrast effect. The Doppler velocity was determined from the Doppler video spectral display and from power spectral analysis of the audio Doppler signal. The Doppler signal intensity was also measured. The Doppler signal intensity increased 17.4 +/- 3.5 dB (p < 0.0001) following echo contrast injection. This was associated with a significant increase in the spectral peak velocity as determined from either the video display or audio analysis. (p < 0.0001). The velocity corresponding to the audio power peak frequency (the modal velocity) did not change significantly (p = NS) and was independent of Doppler signal strength.     

Time to peak velocity measurements by pulsed wave Doppler tissue imaging to quantify ischemia-related regional myocardial asynchrony.

A total of 173 patients with chest pain but without visually discernible wall-motion abnormalities by 2-dimensional echocardiography underwent pulsed wave Doppler tissue imaging examination before angiography. Segmental longest time to peak contraction velocity (Tpv) was acquired through 3 apical views. The longest time period from electrocardiographic R wave to peak velocity on segmental velocity integrals of nonapical segments was measured. Receiver operating characteristic curve analysis was performed for correlation analysis between segmental Tpv and significant (>or=50% luminal diameter stenosis) coronary artery stenosis. Analysis of variance test was used to compare among different patient groups with 0, 1, 2, and 3 coronary artery stenoses. Delay in Tpv on any 1 or more of the 12 nonapical segments was noted in 72 of 116 patients with angiographically significant coronary stenosis. When the longest segmental Tpv of >or=340 milliseconds was selected as a cut-off value for identification of a significant left circumflex or multivessel coronary artery stenosis, the area under receiver operating characteristic curve was 0.69 and 0.72, respectively (P =.000 and.0013, respectively). In conclusion, pulsed wave Doppler tissue imaging technique provides objective quantitative information for identification of multivessel or left circumflex coronary artery stenosis in patients with chest pain but without apparent wall-motion abnormalities on echocardiography.     

Effect of tank liquid acoustic velocity on Doppler string phantom measurements

The quantitative effects of degassed water in string phantom tank Doppler measurements are derived theoretically. The Doppler parameter measurements considered are range gate registration, range gate profile, image flow angle measurements, and velocity calculation. The equipment velocity calculation is demonstrated to have an appreciable error which is due to the water acoustic velocity and the transducer acquisition geometry. A velocity calibration technique is proposed that only needs a simple multiplicative factor to compensate for the water in the tank.     

Intraobserver reproducibility of Doppler measurements of uterine artery blood flow velocity in premenopausal women.

OBJECTIVE: To determine the intraobserver repeatability of Doppler measurements of uterine artery blood flow velocity and the contribution of various factors to within-subject variance. DESIGN: Seventeen healthy premenopausal women underwent vaginal Doppler ultrasound examination of the uterine artery by the same observer. Three measurements were taken at each of three sites: 1) the currently recommended sampling site; 2) the ascending branch of the uterine artery at a level between the lower and middle third of the corpus uteri; 3) 1.5 cm lateral to the recommended sampling site. Three measurements were taken at each site. For each measurement, three uniform consecutive cardiac cycles were analyzed. Peak systolic velocity, time-averaged maximum velocity, and pulsatility index were calculated. Each Doppler shift spectrum was analyzed twice. Thus, for each women, 18 measurement results per sampling site were obtained. Analysis of variance was used. RESULTS: The effect of sampling site on measurements of peak systolic velocity and time-averaged maximum velocity was non-significant, but pulsatility index values obtained at the distal sampling site were slightly higher than those obtained at the other sites (P = 0.01). Repetition accounted for most of the within-subject variance. Averaging the results of the three repeat measurements yielded increased intraclass correlation coefficients: 0.79-0.89 for peak systolic velocity, 0.80-0.92 for time-averaged maximum velocity and 0.86-0.93 for pulsatility index. CONCLUSION: As the effect of repetition on the results of Doppler measurements of uterine artery blood flow velocity is large, the average of several repeat measurements should be used to enhance measurement reproducibility. However, it is not worth doing more than one analysis of a Doppler shift spectrum, and it is not worth analyzing more than one cardiac cycle per spectrum.     

Accuracy of spectral Doppler flow and tissue velocity measurements in ultrasound systems

Blood and tissue velocity are measured and analysed in cardiac, vascular and other applications of diagnostic ultrasound (US). An error in system calibration is a potential risk for misinterpretation of the measurements. To determine the accuracy in velocity calibration, we tested three common commercial US systems using a Doppler string phantom. We tested pulsed and continuous-wave Doppler modes for velocities relevant to both cardiac blood flow and tissue-velocity estimation. The US systems were tested with settings and transducers commonly used in cardiac applications. One system consistently overestimated velocity by about 5%, whereas the other two systems were quite accurate in velocity estimation. These findings emphasize the importance of continuous quality control of US equipment.     

Effects of transducer, velocity, Doppler angle, and instrument settings on the accuracy of color Doppler ultrasound

The accuracy of a commercial color Doppler ultrasound (US) system was assessed in vitro using a rotating torus phantom. The phantom consisted of a thin rubber tube filled with a blood-mimicking fluid, joined at the ends to form a torus. The torus was mounted on a disk suspended in water, and rotated at constant speeds by a motor. The torus fluid was shown in a previous study to rotate as a solid body, so that the actual fluid velocity was dependent only on the motor speed and sample volume radius. The fluid velocity could, thus, be easily compared to the color Doppler-derived velocity. The effects of instrument settings, velocity and the Doppler angle was assessed in four transducers: a 2.0-MHz phased-array transducer designed for cardiac use, a 4.0-MHz curved-array transducer designed for general thoracic use, and two linear transducers designed for vascular use (one 4.0 MHz and one 6.0 MHz). The color Doppler accuracy was found to be significantly dependent on the transducer used, the pulse-repetition frequency and wall-filter frequency, the actual fluid velocity and the Doppler angle (p < 0.001 by analysis of variance). In particular, the phased array and curved array were observed to be significantly more accurate than the two linear arrays. The torus phantom was found to provide a sensitive measure of color Doppler accuracy. Clinicians need to be aware of these effects when performing color Doppler US exams.     

Inter- and intra-observer variability of Doppler peak velocity measurements: an in-vitro study

To determine the variability of pulsed Doppler peak velocity measurements, four radiologists with differing experience were tested using a calibrated flow phantom. Two ultrasound units, three probes and eight velocity rates varying between 40.5 and 78 cm/sec were studied, with a total of 303 measurements. The results were normalized against a set of 106 separate measurements made under highly-controlled conditions. The residual error standard deviation (not attributable to any systematically varied factor, including the velocity rate) was 6.8 cm/sec, with most of the remaining variation due to changing transducer or machine. Observer/equipment interactions accounted for 15.8% of the observed variability. The duration of the radiologist's Doppler experience had no significant effect.     

Pulsed Doppler velocity patterns produced by arterial anastomoses

Centerstream velocity waveforms produced by end-to-end and end-to-side anastomoses constructed in the dog illeofemoral arterial system were studied with a 20 MHz pulsed Doppler velocimeter combined with spectral analysis. Flow disturbance was identified by changes in spectral width during the systolic phase of the cardiac cycle. Measurement of the maximum frequency and the spectral width at peak systole was used to quantify the magnitude of flow disturbance at varying locations proximal and distal to the anastomoses. Disruption of the normal laminar flow pattern observed in the unoperated dog artery was evident distal to both anastomotic configurations. An increase in spectral width reflecting disturbed flow was maximal during the deceleration phase of systole. Flow disturbance was localized to a zone within one diameter distal to the anastomosis and dissipated rapidly downstream. The velocity spectrum changes observed downstream of an anastomosis resemble the flow disturbances produced by low grade, nonpressure reducing arterial stenoses.This study suggests that spectral analysis of pulsed Doppler waveforms is a potentially useful method of anastomosis assessment both to rule out major flow disruption produced by technical error, and to provide insight into the role of turbulence in the development of anastomotic intimal hyperplasia.     

Colour Doppler velocity imaging of the myocardium.

A technique has been developed for producing images of the velocity of tissue motion within the myocardium. It has been demonstrated that Colour Flow Doppler imagers can be operated to depict the velocities within the myocardium rather than moving blood in the cardiac chambers. The technique exhibits the normal advantages of diagnostic ultrasound, i.e., real-time imaging with relatively inexpensive equipment and no hazard to the patient. Further work requires to be done to determine the optimum signal processing algorithms for moving tissue echoes and to ascertain whether the technique is of value in clinical applications.     

Accuracy of velocity and shear rate measurements using pulsed Doppler ultrasound: a comparison of signal analysis techniques.

An experimental investigation was instituted to evaluate the performance of Doppler ultrasound signal processing techniques for measuring fluid velocity under well-defined flow conditions using a 10-MHz multigated pulsed ultrasound instrument. Conditions of fully developed flow in a rigid, circular tube were varied over a Reynolds number range between 500 and 8000. The velocity across the tube was determined using analog and digital zero crossing detectors and three digital spectrum estimators. Determination of the Doppler frequency from analog or digital zero crossing detectors gave accurate velocity values for laminar and moderately turbulent flow away from the wall (0.969 less than or equal to r less than or equal to 0.986). Three digital spectrum estimators, Fast Fourier Transform, Burg autoregressive method, and minimum variance method, were slightly more accurate than the zero crossing detector (0.984 less than or equal to r less than or equal to 0.994), especially at points close to the walls and with higher levels of turbulence. Steep velocity gradients and transit-time-effects from high velocities produced significantly larger errors in velocity measurement. Wall shear rate estimates were most precise when calculated using the position of the wall and two velocity points. The calculated wall shears were within 20%-30% of theoretically predicted values.     

Endoscopic ultrasound Doppler probes for velocity measurements in vessels in the upper gastrointestinal tract using a multifrequency pulsed Doppler meter

To quantify flow velocity in vascular structures in the upper gastrointestinal tract, prototype ultrasound Doppler transducers having frequencies of 5 and 10 MHz were designed. Connected to an advanced pulse ultrasound Doppler meter via an isolation transformer for patient safety, these transducers enabled the recording of flow velocity in vessels within an surrounding the wall of the GI tract. This set up improves the endoscopic ultrasound Doppler method by extending the measurable depth-range by using two frequencies, permitting independent selection of measuring depth and sample volume length, and giving an output format which includes full spectral analysis, simultaneous ECG and capabilities of displaying two additional signals.     

Blood flow velocity vector field reconstruction from dual-beam bidirectional Doppler OCT measurements in retinal veins

In this paper, we demonstrate the possibility to reconstruct the actual blood flow velocity vector field in retinal microvessels from dual-beam bidirectional Doppler optical coherence tomography measurements. First, for a better understanding of measured phase patterns, several flow situations were simulated on the basis of the known dual beam measurement geometry. We were able to extract the vector field parameters that determine the measured phase pattern, allowing for the development of an algorithm to reconstruct the velocity vector field from measured phase data. In a next step, measurements were performed at a straight vessel section and at a venous convergence; the obtained phase data were evaluated by means of the new approach. For the straight vessel section, the reconstructed flow velocity vector field yielded a parabolic flow. For the venous convergence, however, the reconstructed vector field deviated from a parabolic profile, but was in very good accordance with the simulated vector field for the given vessel geometry. The proposed algorithm allows predictions of the velocity vector field. Moreover, the algorithm is also sensitive to directional changes of the flow velocity as small as <1°, thereby offering insight in the flow characteristics of the non-Newtonian fluid blood in microvessels.OCIS codes: (110.4500) Optical coherence tomography, (170.2655) Functional monitoring and imaging, (280.2490) Flow diagnostics     

Doppler frequency shift and time-domain velocity enhancement induced by an ultrasonographic contrast agent.

The aim of this study was to evaluate in rabbit aorta the effect of three bolus doses of Levovist on velocity values measured with spectral Doppler sonography and with time-domain correlation method (color velocity imaging). At each step, a mean peak systolic velocity was calculated from five measurements. These measurements were taken before injection, at 20 s after, at every 30 s till the third minute, and at every minute until return to peak systolic velocity at baseline value. Total duration of enhancement was noted after each injection. After each injection, once the systolic velocity values return to baseline values, a 3 min delay was observed before the following intravenous contrast agent injection was done. With Doppler spectral analysis, after the first injection, peak systolic velocity enhancement was 15 +/- 8.4% (5 to 28%), with a 6.4 +/- 4.3 min duration. After the second injection, peak systolic velocity enhancement was 15.8 +/- 8.4% (5 to 28%) with an 8.8 +/- 4 min duration. After the third injection, it was 14 +/- 9.8% (5 to 34%) with a 13.6 +/- 7.6 min duration (P = 0.04). Peak systolic velocity measured with color velocity imaging remained unchanged after every injection. Doppler velocities were increased by a bolus injection of a contrast agent. Amplitude was not cumulative with the number of injections but was cumulative on its duration. Velocity measurement with time-domain correlation was not influenced by repeated injections.     

25 + 1 channel pulsed ultrasound Doppler velocity meter for quantitative flow measurements and turbulence analysis

A multichannel pulsed ultrasound Doppler instrument designed to measure velocity and volume flow rate quantitatively has been applied for turbulence detection. A 7-MHz transmitting frequency and a phase locked loop technique for the frequency to velocity conversion have been used to obtain high temporal resolution in the single channel mode. To provide for reliable positioning of the single gate within the arterial lumen the device could first be operated in the multichannel mode measuring the velocity profiles with zero crossing detection methods. Measurements of the velocity in the center of the lumen of the common and internal carotid arteries have been recorded on a beat to beat basis. An ensemble average of 16 consecutive pulses was determined. Thereafter, the root mean square of the differences between ensemble average and individual velocity pulses was computed, and a disturbance index was defined by dividing the disturbance velocity by the mean velocity. First clinical results show that the method presented is a valuable complement to the analysis of flow pulse patterns in the transcutaneous examination of carotid arteries.     

Duplex Doppler sonography of the carotid artery: velocity measurements in an artery with contralateral stenosis

To determine if a significant contralateral stenosis affects interpretation tables of the ipsilateral internal carotid artery's degree of stenosis in duplex Doppler ultrasound, the records of 307 patients with carotid duplex ultrasound studies with an angiogram performed within 3 months without intervening intervention were retrospectively reviewed for peak systolic velocity, end-diastolic velocity, internal carotid artery-common carotid artery ratio, and angiographic degree of stenosis. Data were grouped into categories of degree of contralateral stenosis, and Pearson r correlation was used to determine significance of ipsilateral Doppler parameters to angiographic data.As the degree of contralateral stenosis increases, the correlation of ultrasound parameters becomes less significant. At a contralateral stenosis of less than 40%, the P value for peak systolic velocity was 0.0006; at a contralateral stenosis between 40% and 59%, the P value was 0.133; at a contralateral stenosis between 60% and 79%, the P value was 0.241; and at a contralateral stenosis between 80% and 99%, the P value was 0.439. Therefore, correlations are no longer significant at levels above 40% contralateral stenosis. The Doppler parameters were scattered in patients with greater than 40%contralateral stenosis, and "corrected" correlation tables could not be derived. As stenosis increases in the contralateral internal carotid artery, Doppler values become inaccurate in determining the degree of stenosis in the ipsilateral internal carotid artery, with the occurrence of both the overestimation and underestimation of the degree of stenosis.     

Evaluation of Doppler ultrasound for blood perfusion measurements.

The need to develop clinical methods for the noninvasive monitoring of regional blood perfusion, i.e., the blood flow through the very fine capillaries in body tissue, has long been felt. Hitherto existing methods exhibit limitations, such as insufficient measurement depth and poor time- or space-resolution, which restrict the measurements that can be performed. Dymling (1982) introduced a new CW Doppler ultrasound method for noninvasive blood perfusion measurement which might be one possible solution to this problem. Preliminary experiments indicated a correlation between blood flow and measured perfusion value. Unexpectedly large variations in the recorded perfusion values lead to further investigation of the method, both in vitro using a specially designed flow phantom and in vivo. This study indicates that at least some of the large variations recorded are the result of measurement errors caused by movement artifacts or ultrasonic signal interferences. Methods to diminish the effects of these artifacts are discussed.