Impact of temporal resolution on flow quantification by real-time 3D color Doppler echocardiography: numerical modeling and animal validation study

Abstract

Real-time, 30 color Doppler echocardiography (RT3D) i s capable of quantibing flow at the LV outjlow tract (LVOT). However, previous works have found significant underestimation for flow rate estimation due to jinite scanning time (ST) of the color Doppler. We have, therefore, developed a mathematical model to correct the impact of ST on flow quantification and validated it by an animal study.Scanning time to cover the entire cross-sectional image of the LVOT was calculated as 60 ms, and the underestimation due to temporal averaging effect was predicted as 1827%. In the animal experiment, peak flow rates were obtained by spatially integrating the velocity data f o m he cross-sectional color images of the LVOT. By applying a correction factor, there was an excellent agreement between reference flow rate by an electromagnetic flow meter and RT3D (A = -5.6 ml/s, r=0.93, which was signifiantly better than without correction (p< 0.001).Real-time, color 30 echocardiography was capable of quantifiing flow accurately by applying the mathematical correction. IntroductionReal-time, three -dimensional (RT3D) color Doppler echocardiography is capable of quantifying flow velocities in cross-sectional (c-plane) images of the flow tract I. The RT3D system, originally developed in the Duke University Center for Emerging Cardiovascular Technology, utilizes a two-dimensional matrix array probe that electronically scans the ultrasound beam to detect the echo signals from 3D volumetric space in real-time '. The volumetric frame rate of the system is around 25 Hz for B-mode, and 10 Hz for color Doppler imaging, depending on scanning conditions. By using the cross-sectional color Doppler images, calculation of flow rate is possible without any geometric assumptions about flow velocity distributions4.However, previous works have assumed an infinitesimal scanning time to obtain the cross-sectional color Doppler images, and have found significant underestimation for peak flow rate estimation. The aim of the present study was, therefore, to develop a mathematical model to correct the impact of the scanning time or temporal resolution on flow quantification by R n D color Doppler. Methods Numerical modelingFor the numerical modeling, ultrasonic scanning time (ST) to cover the entire cross-sectional area of the flow tract using RT3D was first calculated from the following parameters: pulse repetition frequency (PRF; kHz), packet size of the color Doppler (number of the ultrasound interrogations per scanning line) (PS), and the parallel processing number (PP). E E 0 TP ET' Time Figure 1. Schematic diagram of the temporal flow profile and its relation to the scanning time (ST). Qp: peak flow rate; Tp (Time to peak); ET (ejection time).

The use of live three-dimensional Doppler echocardiography in the measurement of cardiac output

“…However, time-consuming offline processing is required and border detection can still be a source of error. One previous study (24) used an earlier real-time 3-D Doppler system to compute flow at the level of the LVOT. In that study, the low frame rate of the Doppler acquisition, approximately 10 Hz, led to underestimation of flow volume.…”

Real-time 3-Dimensional Doppler Echocardiography for the Assessment of Stroke Volume: An In Vivo Human Study Compared with Standard 2-Dimensional Echocardiography

“…27 Accurate volume calculation from other valves is possible using this realtime 3DE Doppler method. 30 In this study by Ge et al, 30 a nonhigh-density setting was used to increase the size of the 3D pyramid to ensure the capture of the whole of the mitral valve orifice. Capture of the whole of the mitral annulus with a high-density setting may be more difficult.…”

“…Volume calculation was, therefore, inaccurate without a mathematic correction. 30 The system used in this study has frame rates of up to 20 Hz for color Doppler acquisition. This has improved the accuracy of real-time 3DE as shown by our previous animal study 27 and the recent study calculating mitral inflow volumes compared with phase-encoded velocity MRI.…”

Combination of pulsed-wave Doppler and real-time three-dimensional color Doppler echocardiography for quantifying the stroke volume in the left ventricular outflow tract

“…Correction by the temporal constant ␣ Due to the low temporal resolution, the peak flow rate by 3-D color (Q p3D ) is temporally averaged during the volumetric acquisition of the color Doppler data. To correct this averaging effect, a correction factor ␣ was determined by the scanning time (ST) and the temporal waveform of the LVOT (Tsujino et al 2000). For all the hemodynamic stages, volumetric frame rate during the experimental study was 7.9 Ϯ 1.3 Hz, which corresponded to a scanning time (ST) of 63 ms.…”

“…The numerical conditions for the ejection time (ET) and time to peak flow during systole were obtained by using the actual data of the standard PW Doppler from the animal experiment. The details of the temporal correction method are described elsewhere in detail (Tsujino et al 2000). SV was also calculated by the conventional PW method, using the above PW Doppler data for comparison.…”