Jeffrey Kwon

Utility of Three-Dimensional Ultrasound Doppler Flow Reconstruction of the Proximal Jet to Quantify Effective Orifice Area: In Vitro Steady and Pulsatile Flow Studies

We examined the utility of three-dimensional (3D) reconstruction of two-dimensional color Doppler images of the proximal jet to quantify the effective area of an orifice in an in vitro model. Steady and pulsatile flows were directed through various orifices; orifice vena contracta areas were quantified with laser flow visualization, thus providing gold standard effective orifice areas. Three-dimensional areas followed vena contracta areas well, although variations in color Doppler gain and 3D gray levels for thresholding produced significant changes in reconstructed images. These variations were minimized by using minimum color gain and 50% gray level threshold. At these settings, 3D areas still overestimated vena contracta areas by approximately 25% because of the poor lateral resolution of the color Doppler system, which caused bleeding of the flow signal past the edges of the proximal jet. Nevertheless, 3D flow images provided a superior format for qualitative and quantitative appreciation of proximal jet shape and dimensions.

Real-Time 3-Dimensional Volumetric Ultrasound Imaging of the Vena Contracta for Stenotic Valves with the Use of Echocardiographic Contrast Imaging: In Vitro Pulsatile Flow Studies

The purpose of our study was to investigate the utility of real-time 3-dimensional volumetric ultrasound coupled with echo contrast imaging to visualize and quantify effective flow areas for stenotic valves in vitro. Real-time 3-dimensional ultrasound imaging has recently emerged as a promising method for increasing the quantitative accuracy of echocardiography. Since the technique currently does not process Doppler information, its use for quantifying flow has not been studied. However, the use of contrast agents to visualize cardiac flows with the use of echocardiography should allow determination of mass-dependent flow parameters such as effective flow area (vena contracta area) for stenotic lesions. We used real-time 3-dimensional imaging in an in vitro stenotic valve model (areas 0.785 to 1.767 cm2) under pulsatile flow conditions (60 bpm; 40 to 80 mL/beat). An echo contrast agent was used to visualize the distal jet. Real-time 3-dimensional imaging provides simultaneous views of long-axis and short-axis (C-scan) image planes of the jet. The vena contracta was identified and measured by placing the C-scan line immediately distal to the orifice and measuring the cross-sectional flow area. System gain and postprocessing curve shape affected 3-dimensional areas; minimal gain and a custom curve produced best agreement to actual vena contracta areas measured with a previously validated laser method (y = 0.939x + 0.089; r = 0.98; standard error of estimate = 0.158 cm2). We conclude that real-time 3-dimensional ultrasound imaging coupled with a contrast agent can be used as an accurate yet simple clinical means of measuring effective flow areas for stenotic valves.

THREE-DIMENSIONAL ULTRASOUND FLOW IMAGING PROVIDES MORE ACCURATE VISUALIZATION OF THE FLOW CONVERGENCE REGION THAN TWO-DIMENSIONAL COLOR FLOW MAPPING: IN-VITRO STUDIES. |[dagger]| 208

Two-dimensional (2D) color Doppler flow mapping (CDFM) of the flow convergence (FC) region provides important information on regurgitant volumes. However, the 2D view provided by CDFM may not reveal complete FC information especially for complex orifice geometries. We used a Toshiba ultrasound scanner (Nyquist limits (NL): 10 - 60 cm/sec) interfaced to a Tomtec 3D ultrasound reconstruction computer which provides multiple views of structure and flow, to visualize the FC region for pulsatile flow (20 - 90 cc/beat; 50 - 80 bpm) through a variety of orifice sizes (0.1 cm2 - 2.0 cm2) and shapes(circular, oval, Y-shaped). The FC region could be clearly visualized using 3D ultrasound Doppler flow imaging for all hemodynamic conditions at all NLs. Aliasing radii measured from the 3D flow images correlated well with actual flow volumes (y=0.05 x+0.21; r=0.98, NL= 38cm/sec) with best results obtained at intermediate (30 - 50 cm/sec) NLs. Increasing orifice size and decreasing flow rate both caused perceptible flattening of the 3D FC contour within the central convergence region where angle induced velocity errors are minimal. 3D ultrasound flow imaging of the proximal flow convergence region presents both qualitative and quantitative advantages over conventional 2D CDFM and should improve clinical application of this technique.

AUTOMATIC FLOW CALCULATION OF REGURGITANT JETS FROM VOLUME RENDERED THREE-DIMENSIONAL FLOW IMAGES: IN-VITRO STUDIES. 209

Three dimensional (3D) ultrasound flow imaging promises to provide true 3D depiction of regurgitant jets which can then be used to calculate regurgitant volume (RV). Methods: Steady (30 cc/sec - 100 cc/sec) and pulsatile(15 - 40 cc/beat) flows through orifices (0.2 - 1.8 cm2) were imaged using a Toshiba ultrasound scanner interfaced to a Tomtec 3D reconstruction system. 3D flow images were analyzed off-line by first calibrating the color Doppler velocity map to the 3D grey levels. Flow rate was computed by integration of all velocities over the cross-sectional slices of the distal 3D jet which allowed for true mean flows to be obtained with no velocity profile assumptions. Results: 3D calculated flow rates for steady flow correlated well with actual flows with overestimation (y = 3.64x - 0.42; r = 0.985; SEE = 0.51 L/min). 3D flow images of pulsatile flow could be also be used to automatically calculate instantaneous flow rates(Figure) Conclusions: 3D flow imaging of regurgitant jets promises to increase the accuracy of jet volume calculations. Automation of such flow calculations provides an effective and easy method to take advantage of the large amount of information provided by 3D flow imaging.

EFFECT OF MACHINE PARAMETERS ON THREE-DIMENSIONAL VOLUME MEASUREMENT OF JETS: IN VITRO STUDIES. 170

EFFECT OF MACHINE PARAMETERS ON THREE-DIMENSIONAL VOLUME MEASUREMENT OF JETS: IN VITRO STUDIES. 170