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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).
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