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
• Ultrasound clinical Doppler imaging: Overview and limitations
• Advanced vector flow imaging (VFI): Techniques and applications
• Integration of ultrafast imaging and speckle tracking with VFI for
enhanced flow visualization
• Experimental findings utilizing a 128-channel research platform
(Prodigy) for comprehensive flow analysis

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 Doppler
B mode 3D B-mode Tissue Doppler Strain Rate Imaging
Doppler mode

4. Medical Imaging Systems
Modality Real-
time
Non-
Radiation
Flow
Velocity
Mobility 3-D Cost
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 Flow
200 400 600 800 1000 1200 1400
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Tx
Rx
𝑓𝑐 𝑓𝑐 +𝑓𝑑
Doppler Ultrasound
Tx Rx
𝒇𝒅 =
2𝑓𝑐𝑣𝑐𝑜𝑠𝜃
𝑐
Doppler shift
Velocity vector
Center frequency
Sound velocity
Doppler angle
Axial velocity
Lateral velocity
Velocity vector
𝜃
𝒗𝒔𝒊𝒏𝜽
𝒗𝒄𝒐𝒔𝜽
𝒗

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 ↓
Plane Wave Imaging
Focused 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
𝐍𝐂𝐂 (𝐐𝐮𝐚𝐥𝐢𝐭𝐲 𝐢𝐧𝐝𝐞𝐱)
𝐀𝐱𝐢𝐚𝐥 𝐯𝐞𝐥𝐨𝐜𝐢𝐭𝐲 (𝐆𝐨𝐨𝐝!)
Disp.
𝐋𝐚𝐭𝐞𝐫𝐚𝐥 𝐯𝐞𝐥𝐨𝐜𝐢𝐭𝐲 (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
𝑣𝑐𝑜𝑠 𝛼 − 𝜃2 = 𝑢𝑎2 𝑣𝑐𝑜𝑠 𝛼 − 𝜃3 = 𝑢𝑎3
𝑣𝑐𝑜𝑠 𝛼 − 𝜃1 = 𝑢𝑎1
𝜽𝟏
Transducer
𝒗𝐳
𝜽𝟐
Transducer
𝜽𝟑
𝐀𝑣 = 𝑢 ⇒
𝑐𝑜𝑠𝜃1 𝑠𝑖𝑛𝜃1
𝑐𝑜𝑠𝜃2 𝑠𝑖𝑛𝜃2
𝑐𝑜𝑠𝜃3 𝑠𝑖𝑛𝜃3
𝑣𝑧
𝑣𝑥
=
𝑢𝑎1
𝑢𝑎2
𝑢𝑎3
(
𝒗𝒛: 𝑣𝑐𝑜𝑠𝛼
𝒗𝒙: 𝑣𝑠𝑖𝑛𝛼)
NCC-weighted LS → 𝑣 = (𝐀𝑇
𝑊𝐀)−1
𝐀𝑇
𝑊𝑢
Unknowns
Measurement
Unknowns
NCC-weighted Least Squares
Plane wave 𝜽𝟏 Plane wave 𝜽𝟐 Plane wave 𝜽𝟑
NCC: Normalized Cross-
Correlation
𝒗𝒙
𝑢𝑎1 𝑢𝑎2 𝑢𝑎3

17. 17
Laminar flow
v r = 𝑣0[1 −
𝑟
𝑅
2
]
Parameter Value
Number of Tx/Rx channels 128
Array pitch 0.2 mm
Sampling rate 32 MHz
Center frequency 8 MHz
Plane wave angle −𝟖𝒐, 𝟎𝒐, 𝟖𝒐
Pulse repetition frequency 10 kHz
Radius of blood vessel (R) 4 mm
Peak flow velocity (𝒗𝟎) 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
𝐕𝐚𝐱𝐢
𝐕𝒍𝒂𝒕
𝐕𝐯𝐞𝐜
m/s
m/s
𝑽𝐯𝐞𝐜 (Velocity Vector)

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

20. 20
Parameter Vessel 𝜽 = 𝟗𝟎𝒐 Vessel 𝜽 = 𝟓𝟓𝒐
Array element 128 128
Array pitch 0.2 mm 0.2 mm
Sampling rate 32 MHz 32 MHz
Center frequency 8 MHz 6 MHz
Pulse repetition
frequency
10 kHz 9 kHz
Ensemble size 10 10
Plane wave angle [−16o
, 0o
, 16o
] [16o
, −8o
, 0o
, 8o
, 16o
]
Source: https://jdigitaldiagnostics.com/DD/article/view/76511#tabs-5
Source: https://www.s-sharp.com/uploads/
root//Prodigy256system20201126.jpg
in vitro Experiments
Vessel 𝜽 = 𝟓𝟓𝒐
Vessel 𝜽 = 𝟗𝟎𝒐

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 channels 128
Array pitch 0.2 mm
Sampling rate 32 MHz
Center frequency 8 MHz
Pulse repetition frequency 12 kHz
Ensemble size 10
Plane wave angle [−16o
, 0o
, 16o
]
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
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