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| Title:
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Spectral Velocity Estimation using the Autocorrelation Function and Sparse data Sequences |
| Type:
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Article in proceedingsArticle in proceedings |
| Participant(s):
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Technical University of Denmark
Email:
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| Abstract:
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Ultrasound scanners can be used for displaying the distribution
of velocities in blood vessels by finding the power spectrum of
the received signal. It is desired
to show a B-mode image for orientation and data for this has to
be acquired interleaved with the flow data. Techniques
for maintaining both the B-mode frame rate, and at the same
time have the highest possible $f_{prf}$ only limited by the
depth of investigation, are, thus, of great interest.
The power spectrum can be calculated from the Fourier
transform of the autocorrelation function $R_r(k)$.
The lag $k$ corresponds to the difference in pulse number,
so that for lag $k$ data from emission $i$ is correlated with $i+k$.
It is possible to calculate $R_r(k)$ for
a sparse set of emissions, as long as all combinations of
emissions cover all lags in $R_r(k)$. A
sparse set of emissions interleaved with B-mode emissions can,
therefore, be used for estimating $R_r(k)$.
The approach has been investigated using Field II simulation
of the flow in the carotid and femoral arteries.
A 5 MHz linear array transducer with
128 elements, a pitch of $\lambda$ and an element height
of 5 mm was simulated. The autocorrelation was calculated
from the sparse sequence and averaged over a pulse length.
The 1:2 sequence using 2 flow emission for one b-Mode emissions
showed a nearly indistinguishable
spectrum compared to a Fourier spectrum calculated on the full
data. The sparser sequences give a higher noise in the
spectrum proportional to the sparseness of the sequence.
The audio signal has also been synthesized from the autocorrelation
data by passing white, Gaussian noise through a filter designed
from the power spectrum of the autocorrelation function.
The results show that both the full velocity range can be maintained
at the same time as a B-mode image is shown in real time, where
the trade-off between B-mode frame rate and spectral accuracy can be
selected. |
| Published:
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part of: 2005 IEEE Ultrasonics symposium (ISBN: 0-7803-9382-1), pages: 141-145, 2005, IEEE, |
| DOI:
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| Presented at:
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2005 IEEE Ultrasonics Symposium, Rotterdam |
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