Tissue Doppler gated (TDOG) dynamic three-dimensional ultrasound imaging of the fetal heart.

Dynamic three-dimensional (3D) ultrasound imaging of the fetal heart is difficult due to the absence of an electrocardiogram (ECG) signal for synchronization between loops. In this study we introduce tissue Doppler gating (TDOG), a technique in which tissue Doppler data are used to calculate a gating signal. We have applied this cardiac gating method to dynamic 3D reconstructions of the heart of eight fetuses aged 20-24 weeks. The gating signal was derived from the amplitude and frequency contents of the tissue Doppler signal. We used this signal as a replacement for ECG in a 3D-volume reconstruction and visualization, utilizing techniques established in ECG-gated 3D echocardiography. The reliability of the TDOG signal for fetal cardiac cycle detection was experimentally investigated. Simultaneous recordings of tissue Doppler of the heart and continuous wave (CW) spectral Doppler of the umbilical artery (UA) were performed using two independent ultrasound systems, and the TDOG signal from one system was compared to the Doppler spectrum data from the other system. Each recording consisted of a two-dimensional (2D) sector scan, transabdominally and slowly tilted by the operator, covering the fetal heart over approximately 40 cardiac cycles. The total angle of the sweep was estimated by recording a separate loop through the center of the heart, in the elevation direction of the sweep.3D reconstruction and visualization were performed with the EchoPAC-3D software (GE Medical Systems). The 3D data were visualized by showing simultaneous cineloops of three 2D slices, as well as by volume projections running in cineloop. Synchronization of B-mode cineloops with the TDOG signal proved to be sufficiently accurate for reconstruction of high-quality dynamic 3D data. We show one example of a B-mode recording with a frame rate of 96 frames/s over 20 seconds. The reconstruction consists of 31 volumes, each with 49 tilted frames. With the fetal heart positioned 5-8 cm from the transducer, the sampling distances were approximately 0.15 mm in the beam direction, 0.33 degrees approximately 0.37 mm azimuth and 0.45 degrees approximately 0.51 mm elevation. From this single dataset we were able to generate a complete set of classical 2D views (such as four-chamber, three-vessel and short-axis views as well as those of the ascending aorta, aortic and ductal arches and inferior and superior venae cavae) with high image quality adequate for clinical use.

A new ultrasound contrast imaging approach based on the combination of multiple imaging pulses and a separate release burst.

A new ultrasound contrast imaging technique is described that optimally employs the rupture of the contrast agent. It is based on a combination of multiple high frequency, broadband, imaging pulses and a separate release burst. The imaging pulses are used to survey the target before and after the rupture and release of free gas bubbles. In this way, both processes (imaging and release) can be optimized separately. The presence of the contrast agent is simply detected by correlating or subtracting the signal responses of the imaging pulses. Because the time delay between the imaging pulses can be very short, the subtraction is less affected by tissue motion and can be done in real time. In vitro measurements showed that by using a release burst, the detection sensitivity increased 12 to 43 dB for different types of contrast agents. In the presence of a moving phantom, the increase in sensitivity was 22 dB. This new method is very sensitive for contrast agent detection in fundamental imaging mode and, therefore, non-linear propagation effects do not limit the maximum obtainable agent-to-tissue ratio. However, because of the inherent destruction of the contrast agent, it has to operate in an intermittent way. Through experiments, we have demonstrated the potential of the method to achieve simultaneous high sensitivity for contrast detection, i.e., high agent-to-tissue ratio, and high spatial resolution performance for different types of contrast agents.

How does computer-assisted digital wall motion analysis influence observer agreement and diagnostic accuracy during stress echocardiography?

This study assessed interobserver and intraobserver variation and diagnostic accuracy during 25 dipyridamole stress echocardiography tests interpreted with different analysis systems: a) computer display of high frame rate digital cineloops (47 frames/s); b) computer display of lower frame rate digital cineloops (24 frames/s); and c) videotape recordings. The majority of the patients (84%) had documented coronary artery disease with baseline wall motion abnormalities due to previous myocardial infarctions and/or coronary bypass surgery, thus comprising a population with difficult interpretation of stress echocardiography. Diagnostic accuracy was assessed using coronary angiography as reference method. Interobserver and intraobserver agreement was highest when analysis was performed from computer-displayed cineloops, 96 and 92%, respectively, compared to 84 and 80% respectively, using videotape recordings. Sensitivity for identification of coronary artery stenosis was similar using digital cineloops with high frame rate or videotape recordings (67% to 80% for both systems), and tended to be lower using cineloops with lower frame rate for analysis (53%). Inter- and intraobserver differences for wall motion score index were not significantly influenced by the analysis system. We conclude that computer assisted analysis with high frame rate of the displayed cineloops provides optimal observer agreement and diagnostic accuracy in the same range as videotape analysis in patients undergoing stress echocardiography.

Evaluation of reference systems for quantitative wall motion analysis from three-dimensional endocardial surface reconstruction: an echocardiographic study in subjects with and without myocardial infarction.

Six relevant computer-implemented reference systems for three-dimensional quantitative assessment of left ventricular wall motion abnormalities were compared with visual wall motion analysis of two-dimensional images. Endocardial borders were traced in three apical echocardiographic views at end-diastole and end-systole in 10 patients with myocardial infarction and 5 healthy subjects, and three-dimensional reconstruction of endocardial surfaces was performed. End-diastolic and end-systolic surfaces were aligned in a common axis system depending on the reference system, and systolic wall motion was assessed at 1,024 points on the endocardial surface. The localization of abnormal wall motion was displayed in bull's-eye maps, and the area was determined as a percentage of total endocardial area. For each reference system, the segmental concordance between three-dimensional computerized and visual assessment was determined. The best agreement between computerized and visual analysis was obtained with a reference system based on wall motion towards the major ventricular axis, whereas the poorest result was obtained using the center of left ventricular cavity as reference. Correlation between the estimated area of wall motion abnormality and visually determined wall motion score index was best using the aligned center of mitral valve plane as reference (r = .92).

Three-dimensional echocardiography for quantitative left ventricular wall motion analysis: a method for reconstruction of endocardial surface and evaluation of regional dysfunction.

A method for quantitative LV wall motion analysis based on 3-D reconstruction of the LV endocardial surface is presented. The reconstruction is based on a minimum of three transthoracic apical 2-D cineloops of the LV, digitally transferred from the ultrasound scanner to a computer. Images are obtained by rotating the transducer around the LV long axis. Endocardial borders are traced with an automatic edge detection algorithm with manual correction. These borders are used with a specially designed computer algorithm for reconstruction of LV cavity 3-D shape, and LV volumes, ejection fraction, and endocardial surface area can be determined. The end-diastolic and end-systolic endocardial surfaces are compared for analysis of regional wall motion. A threshold value is selected to discriminate between normal and abnormal wall motion. Regional wall motion abnormalities are displayed in a bull's eye plot, and the corresponding endocardial surface area is expressed in percent of the total endocardial area. Phase analysis is performed from reconstruction of the endocardial surface throughout the cardiac cycle, and displays regions with abnormal wall motion as being out of phase with LV volume variation. Thus, LV 3-D reconstruction performed by this method can be used for quantitative analysis of wall motion in several clinical situations, and due to the simplicity of processing the data, can be useful outside the research laboratory.

Model-based estimation of vascular parameters: evaluation of robustness and suitability of models.

Left ventricular performance depends not only on myocardial state, but also on the properties of the systemic arterial tree. These properties can be assessed from recordings of aortic root pressure and flow by the use of appropriate vascular models. Noninvasive estimates of aortic root pressure and flow can be obtained by the combined use of calibrated external subclavian artery pulse tracing and Doppler echocardiography. With recent advances in computer technology, estimation of model parameters are thus accessible in the clinical setting. We discuss the suitability of different parametric vascular models together with methods for adapting these models to the measured aortic root pressure. We compared the results obtained with simple vascular models (three-component modified Windkessel models) with those of five-component models. The simpler models gave less accurate approximation of the measured pressure waveform, but for a representative set of aortic root pressure and flow data, the simpler models provided adequate estimates of the peripheral arterial resistance, the total arterial compliance, and the proximal aortic area compliance. Furthermore, the simpler models are robust for measurement noise with simple estimation algorithms. Distal arterial pressure and flow waveforms are more oscillatory, and for these the five-component model has more robust estimation schemes with more accurate estimated parameters. Hence, we conclude that for clinical noninvasive assessment of aortic vascular properties, the simpler three-component models provide adequate information. For assessment of the peripheral arteries with large oscillations in the flow, the three-component models can give more than 10% error in the compliance estimate and more complex models can be appropriate.

Cross-sectional left ventricular outflow tract velocities before and after aortic valve replacement: a comparative study with two-dimensional Doppler ultrasound.

To assess whether aortic valve replacement (AVR) results in changes in the flow velocity distribution in the left ventricular outflow tract (LVOT), 10 patients undergoing AVR for aortic stenosis were studied. By extracting velocity information from color flow maps as digital data, instantaneous cross-sectional velocity profiles were constructed. Velocity profiles obtained 1 to 3 days before AVR were compared with recordings made 3 months later. The LVOT velocity profiles were variably skewed both before and after surgery, and no systematic or uniform changes could be detected after AVR. The highest velocities were most often localized in the region from the center of the outflow tract diameter toward the septum both before and after surgery. At the time of peak flow the ratio of the maximum to the cross-sectional mean velocity was 1.38 +/- 0.13 before and 1.39 +/- 0.08 after AVR (NS), and the ratio of the maximum to the mean velocity time integral was 1.47 +/- 0.10 before and 1.56 +/- 0.10 after (NS). We conclude that AVR in patients with aortic stenosis does not result in a change in LVOT velocity profiles that will influence stroke volume estimates with the Doppler technique.

Cross-sectional early mitral flow-velocity profiles from color Doppler in patients with mitral valve disease.

BACKGROUND: Cross-sectional flow-velocity profiles from early mitral flow in 20 patients (10 with mitral regurgitation and 10 with mitral stenosis) were constructed from the velocity data from each point in sequentially delayed two-dimensional digital Doppler ultrasound maps. METHODS AND RESULTS: The data suggested that the early mitral flow studied in an apical four-chamber view was variably skewed in both patient groups. The maximum flow velocity overestimated the cross-sectional mean velocity at the same time by a factor of 1.12-1.86. The maximum time-velocity integral was 1.13-1.77-fold greater than the cross-sectional mean time-velocity integral. In patients with mitral regurgitation, the cross-sectional flow-velocity profile appeared to be most skewed at the level of the mitral leaflet tips. The level of the mitral annulus appeared to give the most homogenous flow-velocity distribution in both patient groups. CONCLUSIONS: When calculations of volume flow are based on pulsed Doppler ultrasound recordings with a single sample volume, the possibility of a skewed flow-velocity profile must be taken into account.

Impact of changes in heart rate and stroke volume on the cross sectional flow velocity distribution of diastolic mitral blood flow. A study on 6 patients with pacemakers programmed at different heart rates.

The effect of changes in stroke volume on the cross sectional velocity distribution in the mitral orifice during passive mitral inflow was studied in six patients with total atrioventricular block, atrial fibrillation and VVI pacemakers during periods with different heart rates. The time velocity integrals recorded both in the left ventricular outflow tract and at the mitral orifice decreased significantly as the heart rate was increased from 60 to 80 and from 80 to 100 beats per minute. Instantaneous cross sectional flow velocity profiles were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital ultrasound maps. Each patient had a characteristic cross sectional flow velocity profile in the mitral orifice recorded at the level of the leaflet tips in a four chamber view. The velocity profiles varied between the patients. With increase in heart rate only minimal changes in the flow profiles from individual patients were seen. The maximum velocity through the mitral orifice overestimated the cross sectional mean velocity at the same time by a factor of 1.4-1.9. The maximum time velocity integral overestimated the cross sectional mean by a factor of 1.4-1.8. The observed cross sectional skew varied between patients but did not change significantly with increasing heart rate and decrease in stroke volume.

The velocity distribution in the aortic anulus in normal subjects: a quantitative analysis of two-dimensional Doppler flow maps.

The velocity distribution in the aortic anulus is commonly assumed to be uniform. A skewed velocity profile may have consequences for the accuracy of volume flow estimates by the Doppler echocardiographic technique. To assess this issue, the velocity distribution in the aortic anulus in 12 normal subjects was studied by computer analysis of digital velocity data from two-dimensional Doppler ultrasound flow maps. The velocity profiles in the aortic anulus were found to be flat but slightly skewed, with the highest velocities toward the septum. There was little interindividual variation. Our findings imply that the centerline velocity is the best estimate for the spatial mean velocity at the aortic anulus in normal subjects. The importance of this finding in patients is unknown. In normal subjects, the results suggest that stroke volume might be overestimated by approximately 15% by Doppler echocardiography if the cross-sectional velocity profile is not accounted for.

Instantaneous cross-sectional flow velocity profiles: a comparative study of two ultrasound Doppler methods applied to an in vitro pulsatile flow model.

Two methods based on different techniques for construction of cross-sectional flow velocity profiles from Doppler ultrasound signals were compared: an intraluminal method using pulsed-wave Doppler echocardiography and an extraluminal method using two-dimensional (color) Doppler ultrasound. The methods were applied to an in vitro pulsatile flow model. With the intraluminal method, pulsed Doppler recordings obtained throughout several flow pulses at different positions across a tube were digitized, and cross-sectional flow velocity profiles were obtained by matching the onset of flow velocity at the various positions. With the extraluminal method, cross-sectional flow velocity profiles were obtained by time interpolation between the digital flow velocity data obtained from several flow velocity maps. The first flow velocity map was recorded at onset of flow and the following maps were incrementally delayed with 20 msec from one flow pulse to the next. The time lag caused by the time needed to update each of the flow velocity maps was compensated for by time interpolation between the sequentially recorded flow velocity maps. The cross-sectional flow velocity profiles obtained with the two methods were compared at identical positions within the tube model at equal flow settings and throughout the pulsatile flow periods. At three different flow settings with peak flow velocity of 0.3, 0.5, and 0.7 m/sec, the difference (mean +/- SD) between the obtained velocities were 0.01 +/- 0.04, -0.01 +/- 0.05, and -0.03 +/- 0.07 m/sec, respectively. The findings suggest that cross-sectional flow velocity profiles from pulsatile flow velocity recordings can be obtained equally well with both methods.

Cross sectional early mitral flow velocity profiles from colour Doppler.

Instantaneous cross sectional flow velocity profiles from early mitral flow in 10 healthy men were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital Doppler ultrasound maps. This interpolation allows correction of the artificially produced skewness of velocities across the flow sector caused by the time taken to scan the flow sector for velocity recording of pulsatile blood flow. These results suggested that early mitral flow studied in an apical four chamber view is variably skewed both at the leaflet tips and at the annulus. The maximum flow velocity overestimated the cross sectional mean velocity at the same time by a factor of 1.2-2.2. Also the maximum time velocity integral overestimated the cross sectional mean time velocity integral to the same extent. This cross sectional skew must be taken into account when calculation of blood flow is based on recordings with pulsed wave Doppler ultrasound from a single sample volume.