Mr. Niels Oddershede Profile

Niels Oddershede

M.Sc. at Danmarks Tekniske Univ

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Proceedings Article | 12 March 2007 Paper

In vivo examples of synthetic aperture vector flow imaging

Niels Oddershede, Kristoffer Lindskov Hansen, Michael Bachmann Nielsen, Jørgen Arendt Jensen

Proceedings Volume 6513, 65130A (2007) https://doi.org/10.1117/12.706467

KEYWORDS: Arteries, Transducers, Image resolution, In vivo imaging, Data acquisition, Ultrasonography, Veins, Optical filters, Scanners, Image processing

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The majority of the commercial ultrasound scanners feature blood flow velocity estimation based on the autocorrelation method, yielding estimates of the axial velocity component only. For studying complex flow patterns like arterial bifurcations or venous confluences, 2-D vector velocity estimates would be needed. Synthetic aperture vector flow imaging could potentially provide this. The purpose of this paper is to test the synthetic aperture vector flow imaging method on challenging in-vivo data. Two synthetic aperture in-vivo data sets are acquired using a commercial linear array transducer and our RASMUS experimental ultrasound scanner. The first data set covers the femoral artery and the confluence of the femoral and saphenous vein of a healthy 26-year-old male volunteer. The second shows the carotid bifurcation of a healthy 32-year-old male volunteer. Both 2 second long data sets are processed, and movies of full vector flow images are generated. This paper presents still frames from different time instances of these movies. The movie from the femoral data tracks the accelerating velocity in the femoral artery during systole and a backwards flow at the end of the systole. A complex flow pattern is seen at the junction of the femoral and saphenous vein. The movie of the carotid bifurcation shows high velocities close to the separating wall between the internal and external carotid, and a vortex tendency at the outermost wall. The volume flow through the femoral artery is extracted from the velocity estimates of the femoral data set by assuming the artery is rotational symmetric. An average volume flow just above 500 ml/min was found for the 26-year-old volunteer. This is in agreement with values found in literature.

Proceedings Article | 12 April 2005 Paper

Experimental investigation of synthetic aperture flow angle estimation

Niels Oddershede, Jorgen Jensen

Proceedings Volume 5750, (2005) https://doi.org/10.1117/12.592384

KEYWORDS: Transducers, Ultrasonography, Image resolution, Blood circulation, Virtual point source, Signal to noise ratio, Synthetic aperture imaging, Blood, Water, Velocity measurements

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Currently synthetic aperture flow methods can find the correct velocity magnitude, when the flow direction is known. To make a fully automatic system, the direction should also be estimated. Such an approach has been suggested by Jensen (2004) based on a search of the highest cross-correlation as a function of velocity and angle. This paper presents an experimental investigation of this velocity angle estimation method based on a set of synthetic aperture flow data measured using our RASMUS experimental ultrasound system. The measurements are performed for flow angles of 60, 75, and 90 deg. with respect to the axial direction, and for constant velocities with a peak of 0.1 m/s and 0.2 m/s. The implemented synthetic aperture imaging method uses virtual point sources in front of the transducer, and recursive imaging is used to increase the data rate. A 128 element linear array transducer is used for the experiments, and the emitted pulse is a 20 micro sec. chirp, linearly sweeping frequencies from approximately 3.5 to 10.5 MHz. The flow angle could be estimated with an average bias up to 5.0 deg., and a average standard deviation between 0.2 deg. and 5.2 deg. Using the angle estimates, the velocity magnitudes were estimated with average standard deviations no higher than 6.5% relative to the peak velocity.

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