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Title Investigation of Ultrasound Vector Flow Imaging on a Commercial Platform
Author Pihl, Michael Johannes
Supervisor Jensen, Jørgen Arendt (Biomedical Engineering, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2009
Abstract Estimation of blood flow velocities plays a key role in diagnosing major diseases in e.g. the carotid arteries. However, the velocities estimated using conventional Colour Flow Mapping or Doppler techniques are angle dependent. The Transverse Oscillation (TO) method solves this angle dependency and is able to estimate the transverse velocity component. The TO method is based on a creation of a double oscillating field by using special apodization profiles when beamforming in receive. Previously reported results have been obtained with the experimental scanner RASMUS. To investigate the feasibility of a commercial implementation, the performance of the TO method is investigated based on beamformed radio frequency data from a commercial scanner. The commercial scanner is set up in CFM mode with only minor modifications. The TO estimator has been implemented in C, for increased speed in calculations and for a potential later direct implementation in a scanner. Measurements were performed on a circulating flow rig in order to measure the performance of the estimator and the setup. The estimated transverse profile was compared to the theoretical parabolic flow profile, and the relative mean standard deviation, ~¾, and relative mean bias, ~B , were calculated. A number of parameters were change: Averaging length in the estimator, the number of shots per estimate, transmit focal depth, beam to flow angle, number of transmit cycles, centre frequency, and the transverse lag. The initial setup yielded for the transverse velocity ~¾vx=15.9% and ~Bvx=17.4%. Using a centre frequency of 5 MHz and increasing the number of shots per estimate to 64 reduced the relative standard deviation to 5.4%, whereas the bias was unaffected. At a beam to flow angle of 90± ~¾vxwas 11.4% and ~Bvxwas 20.9%. This is in strong contrast to a conventional velocity estimator. The conventional velocity estimator is not eable to estimate any velocity of significant magnitude. This illustrates the major improvement of the velocity vector estimation the TO methods provides. The results were compared to previously reported simulations and flow rig measurements using the experimental scanner RASMUS by Udesen et al. The results were comparable, with both simulations and flow rig measurements. Adjusting for the differences in parameter values, the relative standard deviations obtained were close to the previously reported values. The bias, however, was somewhat higher. That is due to limitations in the apodization setup. With suggested procedures and optimisation of the setup, this bias can be reduced. Simulations should be performed in order to optimise the double-oscillating pulse-echo field. The present study demonstrates the feasibility of a commercial implementation of the Transverse Oscillation method for real-time vector velocity estimation with expected clinical impact on disease diagnosis and potential benefits in for instance stroke prevention.
Imprint Technical University of Denmark (DTU) : Kgs. Lyngby, Denmark
Pages 156
Original PDF MichaelJohannesPihl_final_thesis.pdf (3.01 MB)
Admin Creation date: 2009-06-18    Update date: 2009-11-04    Source: dtu    ID: 244963    Original MXD