(May 9, 2024) Enhanced Ultrafast Vector Flow Imaging (VFI) Using Multi-Angle Plane Waves

Ultrasound color Doppler imaging has been routinely used for the diagnosis of cardiovascular diseases, enabling real-time flow visualization through the Doppler effect. Yet, its inability to provide true flow velocity vectors due to its one-dimensional detection limits its efficacy. To overcome this limitation, various VFI schemes, including multi-angle beams, speckle tracking, and transverse oscillation, have been explored, with some already available commercially. However, many of these methods still rely on autocorrelation, which poses inherent issues such as underestimation, aliasing, and the need for large ensemble sizes. Conversely, speckle-tracking-based VFI enables lateral velocity estimation but suffers from significantly lower accuracy compared to axial velocity measurements. 

To address these challenges, we have presented a speckle-tracking-based VFI approach utilizing multi-angle ultrafast plane wave imaging. Our approach involves estimating axial velocity components projected onto individual steered plane waves, which are then combined to derive the velocity vector. Additionally, we've introduced a VFI visualization technique with high spatial and temporal resolutions capable of tracking flow particle trajectories. 

Simulation and flow phantom experiments demonstrate that the proposed VFI method outperforms both speckle-tracking-based VFI and autocorrelation VFI counterparts by at least a factor of three. Furthermore, in vivo measurements on carotid arteries using the Prodigy ultrasound scanner demonstrate the effectiveness of our approach compared to existing methods, providing a more robust imaging tool for hemodynamic studies. 

Learning objectives:  
- Understand fundamental limitations of color Doppler imaging. 
- Understand principles behind advanced vector flow imaging techniques. 
- Familiarize with the ultrasound speckle tracking technique and its implications in flow imaging. 
- Explore experiments conducted using multi-angle plane wave ultrafast imaging, specifically utilizing the pulse-sequence mode on a 128-channel ultrasound research platform. 

1. Enhanced Ultrafast Vector
Flow Imaging (VFI) Using
Multi-Angle Plane Waves
Geng-Shi Jeng
Associate Professor
Institute of Electronics
National Yang Ming Chiao Tung University, Taiwan

2. What You Can Learn
•UltrasoundclinicalDopplerimaging:Overviewandlimitations
•Advancedvectorflowimaging(VFI):Techniquesandapplications
•IntegrationofultrafastimagingandspeckletrackingwithVFIfor
enhancedflowvisualization
•Experimentalfindingsutilizinga128-channelresearchplatform
(Prodigy)forcomprehensiveflowanalysis

3. Medical Ultrasound
•1-15 MHz frequency pulse-echo imaging system
•B-mode (Brightness): Anatomy
•Doppler-mode: Motion
•Vascular & Cardiac: Color Doppler, Spectral Doppler, Vector Flow
•Myocardium: Tissue Doppler, Strain Rate Imaging
Color DopplerB mode 3D B-mode Tissue DopplerStrain Rate Imaging
Doppler mode

4. Medical Imaging Systems
Modality Real-
time
Non-
Radiation
Flow
Velocity
Mobility3-DCost
CT ◎ 100k-300k
X-ray ◎ 120k-235k
MRI ◎ ◎ ◎ ◎150k-2M
PET ◎>2M
Ultrasound◎ ◎ ◎ ◎ ◎◎
5k-70k

5. Doppler Effect
Christian Doppler (1803–1853)
https://commons.wikimedia.org/wiki/
https://www.shutterstock.com/zh/image-vector/education-chart-physic-doppler-
effect-sound-658148101
Frequency shift ∝ Velocity

6. Probe
Beam
direction
Blood Flow200 400 600 800 1000 1200 1400
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2


Tx
Rx
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�
Doppler Ultrasound
Tx Rx
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2??????
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Doppler shift
Velocity vector Center frequency
Sound velocity
Doppler angle
Axial velocity
Lateral velocity
Velocity vector
??????
??????�??????�??????
??????���??????
??????

7. Color & Power Doppler
Color Doppler
Color Doppler
Power Doppler
•Color Doppler
•Both velocity amplitude and direction (axial only) are color coded.
•Power Doppler
•Doppler energy is color coded. No velocity magnitude/direction.

8. Spectral Doppler
Continuous Wave (CW) Doppler Pulsed Wave (PW) Doppler
Velocity distribution (spectrum) of a specific direction (CW Doppler) or gated
depth (PW Doppler) as a function of time

9. Color Doppler on Research Platform
Cardiac 4-chamber view
Carotid artery

10. Commercial Vector Flow Imaging (VFI)
https://www.facebook.com/MindrayNorthA
merica/videos/2007450559399979/
V flow BSI
Mindray BK Medical GE
Method Multi-angle Beam
Doppler
Transverse Oscillation (TO)
Doppler
Speckle Tracking
Visualization Trajectory Fixed Arrow Trajectory
Imaging Acquisition Ultrafast Imaging N/A Ultrafast Imaging

11. Ultrafast Imaging (Multi-angle Plane Waves)
M. Tanter, F. Mathias Fink,"Ultrafast imaging in biomedical ultrasound."IEEE UFFC, 2014.
No. of plane waves ↑
Imaging quality ↑
Frame rate ↓
PlaneWave ImagingFocused Beam

12. •Vector flow imaging (VFI)
•Multi-beam, speckle tracking, lateral oscillation,…
•Allow detailed hemodynamics
•Frame rate > 1kHz
•Multi-angle plane-waves + Doppler (Mindray)
•Combining axial velocities for individual steered plan waves
•Drawback (Doppler or Autocorrelation estimators)
•Bias, ensemble-dependent variance (8-12 samples), spectral aliasing
•Visualization: Trajectory or fixed arrow? Robust?
VFI Good Enough?
Ultrafast imaging + Robust velocity estimator +
Robust particle trajectory
Need

13. •Develop ultrafast VFI based on speckle tracking (ST)
•Plane wave imaging using 3-5 angles
•Velocity vector
•Combining axial velocity estimates for individual plane waves
using weighted least squares (WLS).
•Robust superresolution-like particle imaging
• Speckle similarity as a quality index
Our Solution

14. 14
Search region
Kernel
Target Reference
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Disp.
????????????��?????????????????? ��??????��??????�� (Bad!)
Speckle Tracking
NCC: Normalized Cross-
Correlation

15. NCC: Normalized Cross-
Correlation
Proposed Method (LS-ST)
3-angle plane wave
imaging
Axial velocity
estimate using ST
Vector estimate
using least squares

16. Transducer
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Transducer
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)
NCC-weighted LS → �=(??????
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−1
??????
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Unknowns
Measurement Unknowns
NCC-weighted Least Squares
Plane wave ??????
�Plane wave ??????
�Plane wave ??????
�
NCC: Normalized Cross-
Correlation
??????
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??????1 �
??????2 �
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17. 17
Laminar flow
vr=�
0[1−
??????
??????
2
]
Parameter Value
Number of Tx/Rx channels128
Array pitch 0.2 mm
Sampling rate 32MHz
Center frequency 8MHz
Plane wave angle −�
�
,�
�
,�
�
Pulse repetition frequency10kHz
Radius of blood vessel (R)4mm
Peak flow velocity(??????
�) 0.2 m/s
Ensemble size 10
Simulation (Field II)

18. Simulation Result at 60°
LS-ST
Conv-ST
(Conventional
speckle tracking)
-0.2
-0.1
0
0.1
0.2
(m/s)
LS-ACF
m/s
??????
??????�??????
??????
????????????�
??????
���
m/s
m/s
??????
��� (Velocity Vector)

19. 19
Ground truth LS-ACF LS-ST
Particle Flow Imaging at 60°

20. 20
Parameter Vessel ??????=��
�
Vessel ??????=????????????
�
Array element128 128
Array pitch 0.2 mm 0.2 mm
Sampling rate32MHz 32MHz
Center frequency8MHz 6MHz
Pulse repetition
frequency
10 kHz 9 kHz
Ensemble size10 10
Plane wave angle[−16
o
,0
o
,16
o
][16
o
,−8
o
,0
o
,8
o
,16
o
]
Source: https://jdigitaldiagnostics.com/DD/article/view/76511#tabs-5
Source: https://www.s-sharp.com/uploads/
root//Prodigy256system20201126.jpg
in vitro Experiments
Vessel ??????=????????????
�
Vessel ??????=��
�

21. Pulse Sequence Design

22. Real-time Implementation
Pulse Sequence GUI
Python
Interface

23. LS-ACF LS-ST
Arrow-based VFI vs. New Particle Imaging

24. 24
LS-ACF LS-ST
Arrow-based VFI vs. New Particle Imaging

25. 25
Parameter Value
Number of Tx/Rx channels128
Array pitch 0.2 mm
Sampling rate 32MHz
Center frequency 8MHz
Pulse repetition frequency12kHz
Ensemble size 10
Plane wave angle [−16
o
,0
o
,16
o
]
Source: https://www.docknet.jp/media/medical-checkup-23/
in vivo Experiments
Carotid arteries were measured

26. 26
Arrow-based VFI
Color Doppler w/
angle correction
LS-ACF
Conv-ST
LS-ST
Pulsed Wave (PW) Doppler

27. 27
2mm
2mm
(LS-ST)Arrow-based VFI vs. New Particle Imaging

28. Blood Pressure & Flow Measurements
Blood pressure
Cross-section area (A) Volume flow rate (Q)
QA loop

29. What You Need to Know
•Conventional Doppler imaging only detects 1-D velocity component.
•VFI enables visualization of velocity vectors using trajectory or arrow-
based approaches.
•Ultrafast imaging + VFI allow for comprehensive hemodynamics
evaluation.
•Speckle tracking-based VFI provides a promising alternative to current
Doppler-based VFI techniques.
•Prodigy array research platform facilitates seamless integration of pulse
sequences and developed algorithms for advanced flow imaging
analysis.

30. Q&A
WWW.SCINTICA.COM
[email protected]
Please enter your questions
in the Q&A section
Thank You!