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Broad-beam spectral Doppler sonification of the vena contracta using matrix-array technology

A new solution for semi-automated quantification of mitral regurgitant flow volume and orifice area

Thomas Buck, MD, FACC^*,*, Björn Plicht, MD^*, Peter Hunold, MD, Ronald A. Mucci, PhD, Raimund Erbel, MD, FACC^* and Robert A. Levine, MD, FACC

^* West German Heart Center Essen, University Duisburg-Essen, Essen, Germany
Department for Diagnostic and Interventional Radiology, University Duisburg-Essen, Essen, Germany
Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Boston, Massachusetts

View larger version (38K): [in a new window]   Figure 1 Schematic illustrating the proportionality of backscattered Doppler power and cross-sectional area (CSA) of flow: a broad flow (left) with twice the CSA of a narrow flow (right), and therefore twice the volume of moving scatterers encompassed by the sample volume, will return twice the Doppler power.

View larger version (45K): [in a new window]   Figure 2 Principle of the broad-beam spectral Doppler technique. A matrix array with a reduced aperture (active transducer elements in darker gray) transmits a broad beam (top), which is processed differently upon return to provide both a broad measurement and a narrow calibration beam: the full matrix-array aperture is used to form a narrow receive beam during calibration with a narrow sample volume that lies entirely within the regurgitant flow (bottom left), whereas the reduced aperture forms the broad receive beam during measurement with a broad spectral Doppler sample volume encompassing the vena contracta (bottom right).

View larger version (119K): [in a new window]   Figure 3 Automated regurgitant flow analysis software at work in the calibration stage (left) and measurement stage (right). (Top) Touch-screen panel with control keys. (Bottom) In vitro example of a narrow-spectrum Doppler signal from laminar flow at the vena contracta with the automatic border detection algorithm in operation. The measurement bars—S(ystole) and D(iastole)—specify a cardiac cycle of interest and the limits of integration over time. In the calibration stage (left), the software displays mean power and mean pixel intensity within the specified cardiac cycle. In the measurement stage (right), total flow volume (47.8 ml) and average flow cross-sectional area (average cross-sectional area 0.31 cm2) are displayed.

View larger version (17K): [in a new window]   Figure 4 In vitro results for calculated versus actual flow rate in steady flow (top), calculated versus actual regurgitant stroke volume (RSV) in pulsatile flow (middle), and calculated average flow cross-sectional area (CSA) versus known anatomic orifice area and diameter (bottom). See text.

View larger version (127K): [in a new window]   Figure 5 Examples of patient application of the broad-beam spectral Doppler method—maximal velocities. (Top) Patient with ischemic cardiomyopathy and a dilated left ventricle with poor global function and functional mitral regurgitation. Four-chamber view with color Doppler depicts a central regurgitant jet with a narrow proximal jet width in this view (broader in perpendicular views not shown). The power-velocity integral analysis of the manually traced narrow-spectrum vena contracta Doppler signal provided an average flow cross-sectional area of 0.30 cm2 and regurgitant stroke volume (RSV) of 28.7 ml, with a corresponding magnetic resonance imaging (MRI) RSV of 27.9 ml (moderate regurgitation). (Middle) Patient receiving long-term dialysis with degenerated and calcified mitral leaflets but only mildly impaired left ventricular function. Color Doppler showed a large regurgitant jet into the dilated left atrium and reversed flow in the pulmonary vein. The PVI analysis provided a relatively large flow cross-sectional area (CSA) of 0.51 cm2, with an RSV of 35.4 ml (31.5 ml by MRI). Note the importance of the duration of regurgitation on RSV calculation, here causing a smaller RSV relative to the CSA compared with the patient above due to the shorter period of flow of 380 versus 470 ms; the velocities driving flow across the regurgitant orifice are also lower in this second patient, extending only to 4.5 m/s, as opposed to a peak orifice velocity of 5.0 m/s in the above patient (spectral tracings on the right). (Bottom) Patient with ischemic cardiomyopathy and leaflet malcoaptation, with an eccentric wall jet attached to the lateral left atrial wall. The PVI analysis of the vena contracta Doppler spectrum revealed a flow CSA of 0.33 cm2 and an RSV of 23.7 ml (30 ml by MRI). (In all three cases, maximal high pulse-repetition frequency Doppler velocities corresponded with left ventricular-to-left atrial pressure gradients estimated from systolic pressure (top: 508 cm/s vs. 120 mm Hg; middle: 466 cm/s vs. 100 mm Hg; bottom: 500 cm/s vs. 115 mm Hg, assuming a left atrial pressure of 15 mm Hg, or slightly lower, as brachial cuff pressure mildly overestimates left ventricular pressure.)

View larger version (23K): [in a new window]   Figure 6 Patient study results for calculated versus reference values of regurgitant stroke volume (RSV). BB Doppler = broad-beam spectral Doppler; MRI = magnetic resonance imaging.