Conventional Pulsed Wave Doppler Research Articles

Reflected High-intensity Motion Signals: Can This Ultrasound Phenomenon Be Used for Assessment of Left Ventricular Function?

In this pioneer study, we aimed to evaluate the diagnostic role of reflected high-intensity motion signals (RIMS) in the assessment of left ventricular (LV) systolic and diastolic function and to analyze the reproducibility of RIMS. RIMS are also known under the name of "spectral Doppler artifacts" and to date have been attributed only to the category of useless noises. The value of RIMS in the evaluation of LV function was analyzed in 173 subjects (57 healthy volunteers and 116 patients with chronic coronary and myocardial diseases and arterial hypertension). The level of intra- and inter-observer reproducibility of RIMS was assessed according to the Bland-Altman method in 29 subjects. To record RIMS by conventional pulsed wave Doppler, an apical 4-chamber view was used and the sample volume was placed 3 - 4 cm laterally to the left border of the mitral annulus in projection of the pulmonary tissue. Three components of RIMS are visualized with each cardiac cycle: one systolic (Sa) component and two diastolic (Ea and Aa) components. We have found that RIMS registration did not depend on the quality of LV visualization. In patients with adequate visualization of the cardiac structures and in "difficult" patients with poor LV visualization, RIMS recordings were visually equal. In our study, correlations between LV ejection fraction (EF) and Sa and Aa were found; the cutoff value of Sa < or = 13 cm/s and Aa < or = 15 cm/s separated patients with EF < or = 40 % from other subjects with a sensitivity of 88.2 % and 94.1 % and a specificity of 93.0 % (p <.0001) and 76.9 % (p <.0001), respectively. It was shown that RIMS correlate with the LV diastolic function. The Ea cutoff value of < or = 20 cm/s distinguished subjects with a normal diastolic function from patients with a sensitivity of 88.6 % and a specificity of 80.0 % (p <.0001); the cutoff values of Sa < or = 10 cm/s and Aa < 12 cm/s separated patients with a Grade 4 diastolic dysfunction (according to Canadian consensus recommendations) from other subjects with a sensitivity of 81.8 % and 90.9 %, and a specificity of 98.1 % (p <.0001) and 91.8 % (p <.0001), respectively. The combined evaluation of traditional transmitral E/A ratio and RIMS components allow differentiating of all standard stages of LV diastolic dysfunction in an easy and effective way. The level of intra- and inter-observer reproducibility of RIMS appeared to be acceptable. 1. Systolic and late diastolic components of RIMS correlate with LV global systolic function, and all components of RIMS correlate with LV global diastolic function; 2. The reproducibility of RIMS components is at an acceptable level; 3. Combined analysis of transmitral E/A ratio and RIMS components can become a promising approach for easy and effective separation of patients with different grades of diastolic dysfunction.

A nonuniform sampling approach for fast ultrasonic flow imaging.

Conventional Pulsed Wave Doppler (PWD) systems acquire an ensemble of N echoes per beam line at a constant pulse repetition frequency fprf, so that the pulse repetition interval equals Tpri = 1/fpn. The total time span determines the velocity resolution, and Tpri the unambiguous velocity range. The ensemble size N is by approximation inversely proportional to the frame rate, assuming that the system performs interleaving. For a given frame rate, a tradeoff can only be made between velocity resolution and velocity range. We propose an approach that allows increasing velocity resolution or range while keeping the frame rate constant. The approach is based on nonuniform sampling, i.e. sampling with varying sampling intervals. Thus, for a given ensemble size N a larger total time span, which would increase velocity resolution, or a shorter minimal Tpn, which would increase the velocity range, may be chosen. The conventional Doppler signal processing techniques are not compatible with nonuniform sampling. We, therefore, developed a velocity estimation algorithm for arbitrary sampling that is based on cross correlation. Furthermore, an adaptive wall filter was implemented that differentiates between tissue motion and blood flow. The new approach was successfully tested with in vitro and in vivo data.

Dependence of power Doppler image on a high pass filter instrumented in ultrasound machine

The aim of this study was to examine the influence of flow velocity, beam incident angle and a wall motion filter on the intensity of power Doppler image of steady flow in vitro. Power Doppler images of flow were recorded using a 7.5-MHz linear transducer with the fixed repetition frequency, gain and frame rate settings at the velocity levels of 15, 20, 35 and 65 cm/s with the beam incident angles of 30° and 60°. The power ( P) of received Doppler signal was digitized to 25 gray values ( G) for imaging using a wall motion filter with the transfer function: G = a × log P + b ( a, b = constant values). Image intensity was measured at the center of the flow image off-line and compared with the flow velocity measured by conventional pulsed wave Doppler. Below the Nyquist limit, G increased as velocity increased, and G with the incident angle 30° was lower than those with 60°. Overall relationship between the Doppler shift frequency and the image intensity exhibited an excellent correlation when fit to the theoretical curve derived from the filter property ( r = 0.97). The signal intensity of power Doppler image of flow depends upon the mean Doppler frequency shift or the flow velocity and was clearly affected by the wall motion filter.

A new pulsed wave Doppler ultrasound system to measure blood velocities beyond the Nyquist limit

Conventional pulsed wave (PW) Doppler ultrasound systems measure blood velocities unambiguously as long as the velocities are less than the Nyquist velocity. Here, a new PW Doppler ultrasound system is described, which can measure velocities up to 4.5 times higher than the Nyquist velocity. The new PW system presented here utilizes two ultrasound carrier frequencies, such that an appropriate processing of the Doppler frequencies results in an extended mean-velocity range. With this extended mean-velocity information, the complex Doppler signal is interpolated to reconstruct aliased Doppler spectra. The interpolation algorithm has been tested by computer simulations demonstrating the capabilities and limits. The integration into a commercial Doppler scanner allowed the evaluation of the new PW system in real time. In vitro and in vivo tests demonstrate the effective reconstruction of highly aliased Doppler spectra. >

Target velocity estimation with FM and PW echo ranging Doppler systems. II. Systems analysis

For part I see ibid., vol.40, no.4, pp.366-372 (1993). In Part I, the encoding of the velocity and range information into the received and demodulated signals based on transmission of coherent repetitive linear sweep signals, was discussed. In the present work, two different implementations of FM Doppler systems that can be used to obtain velocity profiles are presented. The first implementation is similar to the implementation of a conventional pulsed wave (PW) Doppler system, based on measurement of phase shift (correlation based system): the second implementation is a frequency-domain analog to the PW Doppler system, based on time shift measurements (cross correlation-based system).

Colour flow imaging in the diagnosis of multiple ventricular septal defects.

Thirty one patients with multiple ventricular septal defects were studied by cross sectional echocardiography, conventional pulsed and continuous wave Doppler, colour flow imaging, and left ventriculography to determine the relative diagnostic benefits and pitfalls of each technique. The patients studied had a wide range of congenital heart defects with 19 patients having isolated multiple ventricular septal defects, three with associated tetralogy of Fallot, five with double outlet right ventricle, three with complete transposition and ventricular septal defect, and one with a complete atrioventricular septal defect. In 23 patients the defects were inspected at operation. Cross sectional imaging with integrated pulsed and continuous wave Doppler correctly identified multiple defects in only 12 (39%) patients. In contrast, colour flow imaging was accurate in 24 (77%) patients and left ventriculography in 20 (65%) patients. When patients were subdivided on the basis of relative peak systolic ventricular pressures into restrictive defects (18 patients) and non-restrictive defects (13 patients) the diagnostic value of colour flow imaging was different for each group. Colour flow mapping correctly identified multiple ventricular septal defects in 16/18 (89%) patients with restrictive defects but only 8/13 (62%) with non-restrictive defects. The comparative diagnostic accuracy of left ventriculography was 15/18 (83%) in the restrictive group and 5/13 (38%) in the non-restrictive group. Colour flow imaging was the single investigative technique with the greatest diagnostic accuracy in the diagnosis of multiple ventricular septal defects. It failed to be consistently accurate in defined subgroups with non-restrictive defects as did left ventriculography. The greatest overall diagnostic accuracy in this series was obtained when both colour flow imaging and ventriculography techniques were used in combination in a complementary fashion.