Synthetic_aperture_ultrasound_Imaging

1. Synthetic Aperture
Ultrasound imaging
By : Amirreza Jodeiry
Medical Ultrasound
Dr. Kavehvash
Sharif University of Technology
Spring 2023

2. Table of contents
01 02 03 04
Results
Theory
SAU
Conventional Mode
Introduction Implementation

3. Introduction
01
Conventional Mode ultrasound imaging

4. Theory Ref.
• Synthetic Aperture Ultrasound Imaging
4
Jensen J., Nikolov S., Gammelmark K., Pedersen M.
Ultrasonics 44 (2006) e5–e15
Technical University of Denmark, Center for Fast Ultrasound Imaging

5. Conventional ultrasound imaging
5
• Waves travel through tissue and partly
reflected at each tissue interface
• B-mode: multiple lines of interrogation over
a wide area, each returning echo is assigned
“ a brightness on a grey scale based on Intensity “

6. Beam forming
6
• Form the shape, size and position of the ultrasound beams
• Controlling by generation of electrical signals

7. Beam forming
• Transmission focusing
7

8. Beam forming
8
• Reception focusing
• Delay - sum beamforming

9. Dynamic Reception Focusing
• Reception focusing
• Change electronic focusing delays with time
• Dynamic delays
• At time T focus is at depth(𝐜𝐓/𝟐)
9
9

10. • Axial resolution frequency.
• Lateral resolution Lambda - aperture size - depth
• The acquisition rate speed of sound c
Aperture synthesis
∝
∝
∝
10

11. • One image line at a time
• Resolution :
Aperture synthesis
11
∆𝑥 =
λ
𝐿
𝑧𝑖

12. Conventional Imaging Limits
12
Impossible to focus every where in the image
Dependence on Wave Length – Focul depth – Aperture size
One Image line at a time.
Focus in Transmission

13. A NEW IDEA
Synthetic aperture imaging
A Game Changer
13

14. Synthetic aperture
Imaging
02

15. Synthetic Aperture
15
1950s
Originally conceived for Radar systems
1970s
Initially implemented using digital computers.
Radar – Ultrasound Applications
1990s
Medical US imaging
Intravscular imaging.
2006
Jensen Paper
Implementaion
Real Time SAU imaging
2020
-------------------------
GPU – FPGA

16. SA Radar
9

17. Synthetic Aperture Ultrasound
17
Combine
• Very small aperture (1 element) in Transmit
• Unfocused Beam
• Reception by all elements
19

18. Synthetic Aperture vs Conventional
• Single element is used for transmitting a spherical wave
covering the full image region.
• The received signals can be used for making a low
resolution image.
• Focusing is performed by finding the geometric
distance from the transmitting element to the imaging
point and back to the receiving element
• When a short pulse is transmitted and the echo signal
is received, a round-trip delay is:
18

19. • Resolution :
Synthetic Aperture vs Conventional
17
SAU
Resolution is constant everywhere with the same aperture size.
Conventional
The best resolution is only available at the focal depth
𝑳 𝒛 = 𝟐𝒛𝒕𝒂𝒏
∆𝜽
𝟐
≈ 𝒛. ∆𝜽
∆𝑥𝑠𝑦𝑛𝑡ℎ.𝑎𝑝 ≈
𝐿
2 ∆𝑥 =
λ
𝐿
𝑧𝑖

20. Apodization
• Windowing of aperture
• Lower side lobes (+)
• Wider main lobe (-)
20

21. High Resolution Image
𝐻𝑅𝐼 𝑟𝑝 =
𝑗=1
𝑁𝑥𝑑𝑐
𝑖=1
𝑁𝐸
𝑎 𝑡𝑝 𝑖, 𝑗 , 𝑖, 𝑗 𝑦𝑟(𝑡𝑝 𝑖, 𝑗 , 𝑖, 𝑗)
21
Number of transducer
elements
Number of emissions
Geometric distance
from emitting element to
the imaging point
p =1,2,3,… P
the current point in the
set of P points
Apodization function for
emission i on transducer j
Received signal from
emission i on transducer j
time for transmission and reception. Function of transmitting (i)
element position, direction of propagation (i) and receiving (j)
element position

22. Formulation
2222
• Backpropagation concept
Array measurement of point source wave field
Backpropagation of wave field by time reversal

23. Fourier-domain backpropagation
23
• Backpropagation concept
• 𝑝 𝑡, 𝑥, 𝑧 ∝ 𝑒𝑗(𝑘𝑥𝑥+𝑘𝑧𝑧−𝑤𝑡)
•
𝑤2
𝑐2
= 𝑘𝑥
2
+ 𝑘𝑧
2
• 𝑝 𝑡, 𝑥, 𝑧 = −∞
+∞
𝐴 𝑤, 𝑘𝑥 𝑒𝑗(𝑘𝑥𝑥+𝑘𝑧𝑧−𝑤𝑡)
𝑑𝑘𝑥𝑑𝑤
𝑃 𝑤, 𝑘𝑥, 𝑧 =
1
4𝜋2
−∞
+∞
𝑝 𝑡, 𝑥, 𝑧 𝑒−𝑗(𝑘𝑥𝑥−𝑤𝑡)
𝑑𝑥𝑑𝑡
• 𝑃 𝑤, 𝑘𝑥, 𝑧 = 𝐴 𝑤, 𝑘𝑥 𝑒𝑗𝑘𝑧𝑧
23

24. Wave field extrapolation
24
• 𝑃 𝑤, 𝑘𝑥, 𝑧 = 𝑃 𝑤, 𝑘𝑥, 𝑍 𝑒𝑗𝑘𝑧 (𝑧−𝑍)
• 𝑘𝑧 =
𝑤2
𝑐2 − 𝑘𝑥
2
• 𝑝 𝑡, 𝑥, 𝑧 = −∞
+∞
𝑃 𝑤, 𝑘𝑥 , 𝑍 𝑒𝑗𝑘𝑧 𝑧−𝑍
. 𝑒𝑗(𝑘𝑥𝑥−𝑤𝑡)
𝑑𝑘𝑥 𝑑𝑤
𝑖𝑝 𝑥, 𝑧 =
−∞
+∞
𝑃 𝑤, 𝑘𝑥 , 𝑍 𝑒𝑗𝑘𝑧 𝑧−𝑍
. 𝑒𝑗𝑘𝑥𝑥
𝑑𝑘𝑥 𝑑𝑤
24

25. Final Flow Chart
25
• The recorded wave field is first Fourier
transformed.
• For every depth 𝑧 of interest, the wave field is
extrapolated to 𝑧
• Integrated over 𝑤, and inverse Fourier
transformed, producing a focused image line
𝑖𝑝 𝑥, 𝑧
25

26. Penetration problem
• Single Element
• Solution : Combining several elements for transmission and
using longer waveforms emitting more energy.
26

27. Flow Estimation
• In SA imaging, it is possible to focus the
received data in any direction and in any
order. It does not have to be along the
direction of the emitted beam, since the
emission is spherical and illuminates the
full region of interest.
27

28. Results
03

29. Angular Resolution
–
40 –
30 –
20 –10 0 10 20 30 40
0
–10
–20
–30
–40
–50
–60
–70
Level
[dB]
boxcar/hanning
–30
–40
–50
–60
–70
–20
–10
0
Level
[dB]
–40 –30 –20 –10 10 20 30 40
boxcar/boxcar
2 emissions
4 emissions
8 emissions
16 emissions
32 emissions
64 emissions
Angular resolution of a SA imaging system for different number of emissions, when using a boxcar apodization in transmit and a boxcar (bottom) or
Hanning apodization in receive (top)
Jensen J., Nikolov S., Gammelmark K., Pedersen M. Ultrasonics 44 (2006)e5–e15
29

30. Low resolution images combined to produce a high resolution image. One element transmit at the time, while all are used to receive.
The images are then added into one high resolution image
Field II simulation Results
3030

31. Implementation
04
Foreign policy 2XXX

32. Attempt for implementation
• First Official Device : RASMUS
• All conventional US imaging methods can
be implemented with this system, but
Real-time SA imaging is not possible.
32

33. Implementation
3333

34. Implementation
Amount of Calculations of SAU
1) Transmit – Receive :
2) Focusing delay
3) Apodization value
4) Interpolating the sample value
5)Summing to other values
Nc=kNl Ne 4f0
3434
𝑁𝑙 = 200 𝑁𝑒 = 192 𝑓0 = 5𝑀𝐻𝑧 𝑘 = 0.8

35. Xilinx Solution
Could be better than GPU.
3535

36. Xilinx Versal ACAP
36
•SA and PW beamformer on Versal™ for
Ultrafast B-mode and Flow imaging
•Associated C++ and Python classes to
produce the SA and PW design
•Frame rates in the range of 1000 fps in a 64
channel architecture on a single Versal using
50% of the available AI Engines in Versal
36

37. AI Engine : Tensor Representation
Vector
(Tensor 1D)
1
Scanline
Matrix
(Tensor 2D)
128
Scanlines
Cube
(Tensor 3D)
128
Scanlines
128
Cube of Cubes
(Tensor 4D)
128
Scanlines
1200
Sample
s
1200
Sample
s
1200
Sample
s
1200
Sample
s
3737

38. FE Block Diagram
64
Channels
Transducer
Array
Transmitter
1
Channel
1
10 nF
T/R Switch
T/R Switch
INP1
Clamping
Diode
Transmitter
32
Channel
32
10 nF
INP32
Clamping
Diode
T/R Switch
Transmitter
64
Channel
64
10 nF
Clamping
Diode
AFE 1
AFE 2
INP32
SPI Control
/TX_TRIG
LVDS
Receiver
LVDS
Lines
ACAP
LVDS
Lines LVDS
Receiver
Clock
Generator
Data
Processing
and
Storage
3838

39. 4 Kernels
Beamforming Image
Front End
Programmable
Logic
AI Engine to
DDR Mover
Calculate the
Points for a
Scan Line
Calculate
Focused Field for
Virtual Sources
Control and Scheduling
Transducer
RF Data
Find Transit
Delay for the
Line
Dynamic
Apodization
Add Receive
Delay Time to
Transmit Delay
Calculate
Apodization
Interpolate
Samples
Sum Interpolated
Samples by
Apodization
For Each Line
128 Lines
Processor
Cortex-A72
For All Elements
32 Elements
Calculate Calculate
Apodization FiFo Delays
iFo
F
Graph Structure
3939

40. The last word
4040

41. Thanks!
Do you have any questions?
Amirreza.Jodeiry@gmail.com
Foreign policy
2X
XX

42. ● Jørgen Arendt Jensen, Svetoslav Ivanov Nikolov, Kim Løkke Gammelmark, Morten Høgholm
Pedersen,Synthetic aperture ultrasound imaging, Ultrasonics,Volume 44, Supplement,2006, Pages e5-
e15, ISSN 0041-624X
● G. Corradi and J. A. Jensen, "Real Time Synthetic Aperture and Plane Wave Ultrasound Imaging with the
Xilinx VERSAL™ SIMD-VLIW Architecture," 2020 IEEE International Ultrasonics Symposium (IUS), Las
Vegas, NV, USA, 2020, pp. 1-4, doi: 10.1109/IUS46767.2020.9251749.
● I. Trots, A. Nowicki, M. Lewandowski, and Y. Tasinkevych, ‘Synthetic Aperture Method in Ultrasound
Imaging’, Ultrasound Imaging. InTech, Apr. 11, 2011.
● Skjelvareid, M.H. Synthetic Aperture Ultrasound Imaging with Application to Interior Pipe Inspection.
Ph.D. Thesis, Universityof Tromsø, Tromsø, Norway, 2012.
References
42