2E1-5
Volumetric Imaging of Superficial Micro-vasculatureusing High-frequency Array Transducer: PhantomStudy
Anam Bhatti1‡, Takuro Ishii1,2, and Yoshifumi Saijo1(1Grad. School of Biomed. Eng., Tohoku Univ.; 2Frontier Research Inst. forInterdisciplinary Sciences, Tohoku Univ.)
1. Introduction
The advent of ultrafast acquisition techniquesin conjuction of spatiotemporal clutter filter based on
singular value decompostion (SVD) has sigificantly
enhanced the sensitivity of Doppler ultrasound invisualization of micro-vessels. This combined
approach provides new diagnostic markers fornumerous preclinical and clinical applications1). The
advancements realized in 2D ultrasound imaging canalso be extended to 3D volumetric ultrasoundimaging, enabling a comprehensive evaluation of
micro-vasculatures in disease diagnosis and its
progression.
3D Doppler volumetric imaging has beenpreviously reported for brain functional imaging, via
step-by-step scanning approach to observe the tumor
vasculature1). However, this iterative translation
approach leads to prolonged acquisition time and ismainly applicable to stationary objects such as small
animal scanning. Recently, a continuous translation
approach for 3D volumetric imaging has been
introduced by Chen et al2). This involves thecontinuous translation of a 1D transducer at aconstant speed to generate stacks of B-mode images.
However, the former approach encounteredchallenges in terms of image quality attributed tointerference noises caused by the translation of probe,
ultimately affects the visibility of micro-vessels.
In this study, we observed the feasibility of 3D
volumetric imaging via continuous mechanicaltranslation, specifically aimed to visualize
superficial micro-vasculatures. To overcome thelimitation of interference noises we introduced anon-local means (NLM) filter3) to effectively
eliminate the noises and improves the sensitivity andvisibility of micro-vasculatures.
2. Method
Fig.1 illustrates the workflow of the
proposed approach of 3D volumetric imaging using
1D high-frequency ultrasound (HFUS) transducer
that mechanically translate continuously at aconstant speed of 1 mm/s and 2 mm/s.
2.1 Imaging System:
A research purpose ultrasound imaging
E-mail: ‡anam.bhatti.q8@dc.tohoku.ac.jp

Fig. 1. Flow chart of 3D volumetric imaging forvisualization of superficial micro-structures.

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. 2500
compound frames were obtained at pulse repetition
frequency of 5 kHz. Each frame was compounded by
10 steered plane waves. The start of the acquisition
was synchronized with the triggering of the vantageand motorized translation stage. A straight tube
micro-phantom (200-micron) at the depth of 4 mm
was fabricated to mimic the superficial
microvasculature. To enable the flow within themicro-tract, a flow circuit assembly comprised on
syringe pump and tubing was connected with microphantom. This assembly facilitated the infusion offlow at a rate of 10 mm/s. To translate the transducer
in elevational direction (distance 5 mm and 10 mm),the probe was mounted via 3D printed probe holder

with 2D stage (OSMS(CS)20-35, Sigmakoki Co.),
which was controlled by controller (SHOT-302GS,Sigmakoki Co.) to translate the transducer
continuously with a constant speed of (1 mm/s and 2mm/s).
2.2 Processing:
Acquiredvolumetricdata
waspreprocessed by dividing into subsequent sections toextract the desired flow signal efficiently via singularvalue decomposition (SVD) based clutter filtering.
Preprocessing of data illustrated in Fig. 1 shows thatthe 12 sections (250 frames = 0.5 s) were createdbased on the acquisition time (2500 frames = 5 s)with overlap of (50 frames = 0.05 s). Each frame wasthen processed with SVD as shown in Fig.1. Later,
an established NLM filter4) was implemented oneach section to remove the interference noises. Once
all the sections were processed with combinedalgorithm of SVD and NLM, a 3D matrix werecreated to visualize the obtained flow structures in
MATLAB built-in application of volume viewer.

dependency on the transducer speed, as evidenced by
the volumetric images in Fig.2. Volumetric dataacquired at a transducer speed of 1 mm/s Fig.2(a-b)
comprised fewer noises compared to that obtained at
2 mm/s Fig.2(c-d). In both instances, the NLM filter
effectively eliminates interference noises leading toa twofold enhancement in image contrast comparedto the images without NLM processing as shown inFig.3.

Fig. 3. Quantitative comparison of contrast-to-noise
ratio among SVD and SVD + NLM under two
conditions of transducer speed (1 mm/s and 2 mm/s).

Fig. 2. 3D rendered volumetric images of 200micron flow tract. (a – b) 3D images obtained withtransducer speed of 1 mm/s, (c-d) 3D images
obtained with transducer speed of 2 mm/s.

3. Results
3D realization of superficial volumetric
imaging of micro-structures through continuous
mechanical translation, as depicted in Fig.2, reveals
that the higher transducer motion speed leads toincreased interference noises. Furthermore, thepower Doppler image of each section, processedusing SVD clutter filter and SVD + NLM filter
presented in Fig.1(c), indicates that the applicationof the NLM filter effectively mitigates theinterference noises resulting from the probetranslation. Notably, these noises exhibit a4. Conclusion
This study demonstrates the feasibility of3D volumetric imaging of superficial microvasculaturesusing
continuous
mechanicaltranslation. The integration of the NLM filter into
this approach substantially improves the imagecontrast, evident both in the qualitative assessment
in Fig.2 and in the quantitative results shown in Fig.
3. Based on these findings, the proposed approach
can be utilized in the 3D volumetric visualization ofsuperficial microvasculature to observe thecomprehensive vascular structures in the diagnosis
and prognosis of diseases.
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