In this PhD project new ultrasound techniques for blood flow measurements
have been investigated in-vivo. The focus has mainly been on vector velocity
techniques and four different approaches have been examined: Transverse
Oscillation, Synthetic Transmit Aperture, Directional Beamforming and Plane
Wave Excitation. Furthermore two different adaptive spectral estimators have
been investigated: Blood spectral Power Capon method (BPC) and Blood
Amplitude and Phase Estimation method (BAPES).
The novel techniques investigated in this thesis are developed to circumvent
some of the main limitations in conventional Doppler ultrasound. That is angle
dependency, reduced temporal resolution and low frame rate.
Transverse Oscillation, Synthetic Transmit Aperture and Directional
Beamforming can estimate the blood velocity angle independently. The three
methods were validated in-vivo against magnetic resonance phase contrast
angiography when measuring stroke volumes in simple vessel geometry on 11
volunteers. Using linear regression and Bland-Altman analyses good
agreements were found, indicating that vector velocity methods can be used
for quantitative blood flow measurements.
Plane Wave Excitation can estimate blood velocities angle independently with
a high frame rate. Complex vessel geometries in the cardiovascular system
were explored in-vivo on four volunteers using the technique. Flow patterns
previously visualized with magnetic resonance angiography and predicted by
models of computational fluid dynamics, were shown for the first time with
ultrasound. Additionally, new information on complex flow patterns in
bifurcations and around venous valves was discovered.
BPC and BAPES are adaptive spectral estimators which can produce
spectrograms with a high temporal resolution. Spectrograms obtained in-vivo
with the two techniques on ten volunteers were evaluated quantitatively and
qualitatively and compared to the conventional spectral Doppler method.
Descriptive statistics, kappa statistics and multiple t-tests were performed and
it was shown that BAPES and BPC can produce useful spectrograms with a
narrower observation window compared to the conventional spectral Doppler
The thesis shows, that novel information can be obtained with vector
velocity methods providing quantitative estimates of blood flow and insight in
to the complexity of fluid dynamics. This could give the clinician a new tool in
assessment and treatment of cardiovascular diseases. Also solutions to
produce spectrograms with fewer emissions per estimate were given. This
could potentially bring improvements to spectral blood estimation as an
increase of the temporal resolution of the spectrogram or as an increase of the
frame rate for the interleaved B-mode images.