3Pb5-2
Visualization of subcutaneous flow tract using SVD filteringof ultrafast high-frequency ultrasound imaging
Anam Bhatti1‡, Naoya Kanno1, Hayato Ikeda1, Takuro Ishii1,2, and Yoshifumi Saijo1(1Grad. School of Biomed. Eng., Tohoku Univ.; 2Frontier Research Inst. forInterdisciplinary Sciences, Tohoku Univ.)

1. Introduction
In the diagnosis of cutaneous disorders,visualization of vasculatures plays a pivotal role inthe determination of the diseases. High-frequency
ultrasound (HFUS) has been used in skin imaging
to visualize the morphology and subcutaneousstructures. However, visualization of vasculatures in
HFUS b-mode imaging is challenging because ofminute dimension of the vasculatures. These
superficial structures can be visualized by mapping
the blood flow signal using highly sensitive
Doppler ultrasound imaging.
Recently, ultrafast Doppler imaging1) is
gaining huge interest in detection of slow-time slow
moving flow signal in vasculatures due to its higher
spatio-temporal resolvability. Although, thistechnique has higher sensitivity to detect theslow-flow signal, but an efficient clutter filter isalso required to extract the slow-time signal
efficiently from the ultrafast Doppler data.
Demene et al2), reported in their study thatthe spatio-temporal clutter filter such as singularvalue decomposition (SVD) outperformed than theconventional temporal based clutter filter in theextraction of slow-time signal from ultrafast
ultrasound data.
In this study, we devised an imaging
framework, based on HFUS ultrafast imaging inorder to achieve high resolution and highly
sensitive images to extract the slow-time signal
efficaciously by implementing SVD clutter filter
which eventually assist in the visualization ofsubcutaneous vasculatures.
2. Materials and Methods:of blood mimicking fluid at rate of (1.88 ml/min
and 0.47 ml/min) with flow speed of 10 mm/s

Fig. 1 Schematic diagram of an imaging setup to
optimize the system for detection and extraction of flow
tract in 2 mm and 1 mm PVA phantoms at flow speed of
10 mm/s by HFUS ultrafast Doppler imaging.

from the respective flow channels. A flow circuitassembly used (plastic tubes 2.5 mm, luer
connectors 2.5 mm and 26 G needle) to connect theinfusion-pump with flow tract and to pass the flowfrom the channel without any leakage as shown inFig.1
2.2 Signal Acquisition and Processing:
The ultrafast Doppler signal was acquired
and process from the respective flow tract, under
two experimental conditions shown in Tab.1 toevaluate the Doppler sensitivity of the devised
imaging framework and the performance of theSVD clutter filter in extraction of slow-time slow
flow signal.

2.1 Imaging System
A HFUS ultrafast imaging setup
comprised of research purpose ultrasound imaging
system (Vantage 256, Verasonics Inc., Kirkland,WA, USA) equipped with L38-22v CMUT (KOLOsilicon, USA) linear array transducer was used fortransmission and reception of ultrasonic signal. Astraight tube PVA phantom of two different coredimensions (2 mm and 1 mm) at depth of 4 mm
were designed and fabricated by following theprotocol by Ho Chung et al3) and a flow setup
which includes an infusion pump to infuse the flow

Tab.1. Data acquisition parameters under two
experimental conditions to evaluate the Doppler
sensitivity of the devised imaging framework.

2.2.1 Experimental Condition 1:
In the acquisition of the signal, 128

channels of the transducer were excited at 30 MHzof center frequency to transmit the plane wave
pulses (3 cycles) at pulse repetition frequency(PRF) of 3 MHz, and 14 Doppler ensembles wereacquired to process by implementing regression
clutter filter of second order (quadratic basis) toextract the signal from the respective flow tract.
2.2.2 Experimental Condition 2:
Instead of transmitting single plane wave,
3 plane waves were transmitted which werecoherently compounded at the reception to quantify
the intensity of the signal content. The acquisition
parameters were same as in condition 1, except thesize of the Doppler ensembles were increase from
14 to 35 ensembles. Also, to estimate thesignificance of the clutter filter in the extraction ofslow-time signal, the acquired ultrafast data wasprocessed by implementing singular value
decomposition (SVD) clutter filter.
3. Results
The power Doppler images obtained fromtwo experimental conditions presented in Fig.2
shows that the coherently compounded and higher
ensemble size of ultrafast data increases theintensity of the Doppler signal. Fig.2(a) shows thepower Doppler images of 2 mm and 1 mm flow
tracts, have poor intensity of the detected signal
which is acquired with plane wave along with lower
ensemble size and processed with regression clutter
filter. Whereas in Fig.2(b) the detected signal has
higher intensity which is processed with SVD
clutter filter.
Moreover,Fromthequantitative
measurements shown in Fig.3. It was observed thatthe signal-to-noise ratio (SNR) of the detectedsignal is higher when the data is acquired withultrafast compounding and higher number ofDoppler ensembles. This measurement indicatesthat the Doppler sensitivity of the framework in
detection of slow-time signal depends on thenumber of acquired ensembles as well as thecompounding angles which enhances the signalquality.
4. Conclusion:
In this study, we devised an imaging
framework to extract the slow-time slow flow
signal by implementing an SVD clutter filter.
Qualitative Fig.2 and Quantitative Fig.3
measurements indicates that the devised imaging
framework has improved performance to detect thesignal from respective flow tract (2 mm, 1 mm) atdepth of 4 mm by ultrafast compounding techniqueand SVD filtering. Based on these observations, it

can be utilized in the visualization of in-vivo
subcutaneous flow tract by further optimizing thesystem acquisition parameters.

Fig. 2 Power Doppler images obtained by two
experimental conditions. (a) Experimental condition 1.
(b). Experimental condition 2.

Fig. 3. Signal-to-noise ratio (SNR) measurement of planewave, plane wave compounding, small number of
Doppler ensembles, and higher number of Doppler
ensembles. (a). SNR measurement from 2 mm flow tract.
(b). SNR measurement from 1 mm flow tract.

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