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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Chuan Chen (RadboudUMC)
Gijs A.G.M. Hendriks (RadboudUMC)
Stein Fekkes (RadboudUMC)
Hendrik H.G. Hansen (RadboudUMC)
Chris L. de Korte (RadboudUMC)

Abstract:
Introduction: Doppler imaging is used routinely for visualizing vascularization and quantifying blood flow. Full-view Doppler is subject to low framerates and has low sensitivity for detecting low velocities. Recent development of ultrafast ultrasound extensively increased the framerate, and 2D studies have shown that in combination with eigen-based filtering it also improves Doppler performance at low blood velocity, a technique called ultrasensitive Doppler. We extended this technique to 3D by mechanical translation of the probe to enable volumetric scanning of low blood velocities, and investigated the impact of the translation speed of the probe on Doppler performance. Method: We designed a prototype consisting of an L7-4 ultrasound linear array transducer translated orthogonally to the imaging plane (elevational direction) by a stepper motor. While being translated, the transducer transmitted steered plane waves in packages of 9 angles, which data were compounded in receive resulting in 500 high resolution images per second. Acquired signals were decomposed using a typical eigen-based filtering, singular value decomposition (SVD), to separate the slow blood signals from tissue clutter and noise signal. A theoretical model was developed which considers the effects of beam slice thickness, translation speed, and SVD settings. Our theoretical model was experimentally evaluated using data acquired on phantoms, in which water containing ultrasonic scatterers was pumped resulting in flow velocities of 5 and 10 cm/s through two approximately perpendicular 4 mm-diameter tubes. Probe translation speeds were changed from 0.5 cm/s to 1 cm/s, in addition to the stationary 0 cm/s case for reference. The accuracy of the obtained Power Doppler images was quantified in terms of Contrast-to-Noise Ratio (CNR) between delineated flow regions and background regions. Results: At a flow velocity of 5 cm/s, the measured CNRs were 2.32, 2.01 and 1.87 for translation speeds of 0, 0.5 and 1 cm/s, respectively. At 10 cm/s flow velocity, corresponding values were 2.84, 2.54 and 2.15. Discussion: We developed 3D ultrasensitive Doppler method based on multi-plane ultrafast ultrasound and eigen-based filtering. More accurate Power Doppler was produced for slower translation speeds and for higher blood velocities. This was theoretically expected because smaller Doppler phase shifts need to be captured by longer acquisition periods.