1. Chapter3 Pulse-Echo Ultrasound Instrumentation
윤성수

2. contents ▣ Pulse-Echo Ultrasound
□ Pulsing Characteristics and Duty Factor
▣ Instrumentation
□ Beam former
□ Pulse Transmitter
□ Receiver
▣ Ultrasound scanning
▣ Scanners
□ Linear array transducers
□ Curvilinear array transducers
□ Phased array transducers
▣ Frame rate and scanning speed limitations

3. Pulse-Echo Ultrasound
□ The Range Equation
□ T : Pulse Echo travel time
□ c : speed of ultrasound
in target material

4. Pulse-Echo Ultrasound
□ Pulse Duration
Pulse Duration↓ ⇒ Axial resolution↑
□ Pulse repetition period
: Wait for Echo pulse
PP↑ ⇒ frame rate ↓
□ Duty Factor

5. Instrumentation

6. Beam former

7. Beam former □ 구현 방식 ▶ Analog vs Digital
□ Beam steering and focusing (pulse delay sequence)
▶ transmit focusing
▶ dynamic focusing of received echo
▶ controls the beam direction

8. Beam former □ 구현 방식 ▶ Analog
①반사신호를 한 곳에 모으는 시간이 20~40ns로 편차가 커 선명한 의료영상 구현 어려움
② 인체 한 부위의 초점 위치를 제외한 나머지 부위에 대해선 수신 focusing을 구현할 수 없음

9. Beam former □ 구현 방식 ▶ Digital Stable : external factor
(ex. temperature)
② programmability
③ wide range of signal frequency

10. Beam former □ Beam steering and focusing (pulse delay sequence)
▶ transmit focusing
▶ dynamic focusing of received echo
▶ controls the beam direction
array
transmitter
focusing
different time delay
Transmit focusing

11. Beam former □ Beam steering and focusing (pulse delay sequence)
▶ transmit focusing
▶ dynamic focusing of received echo
▶ controls the beam direction
different time delay
array
transducer
same delayed
signal
focused signal
reflector
Dynamic focusing of received echo

12. Beam former □ Beam steering and focusing (pulse delay sequence)
▶ transmit focusing
▶ dynamic focusing of received echo
▶ controls the beam direction
Controls the beam direction

13. Pulse transmitter

14. Pulse transmitter □ Pulse transmitter
▶ provide electrical signals for exciting transducer
① Transmit power ↑
② Higher intensity sound wave
③ Higher amplitude echo signal
④ Appear brighter and weaker reflectors In the display
But acoustical exposure to the patient↑

15. Pulse transmitter □ Pulse transmitter
▶ provide electrical signals for exciting transducer
Low output power (MI is 0.2)
High output power (MI is 0.8)

16. receiver

17. receiver
□ Procedure of the receiver

18. amplify(Receiver) □ Preamplifier Boosts echo signals
protect the receiver from high-voltage
□ problem : amplify noise

19. compensate(Receiver)
□ Gain adjustments
▶ Overall gain control
: Increase amplification at all depths
High gain
Low gain

20. compensate(Receiver)
□ Gain adjustments
▶ Overall gain control
: Increase amplification at all depths
(위의 사진 transmit pulse, 아래사진 gain조절) Transmit pulse의 amplitude를 키우는 것과 같은 효과
하지만 인체에 미치는 영향이 없음
High gain
Low gain

21. compensate(Receiver)
□ Gain adjustments
▶ Swept gain or TGC(time gain compensation)
: Attenuation compensation depending depth

22. compensate(Receiver)
□ Gain adjustments
▶ Swept gain or TGC
▶ Slider bar TGC control

23. compensate(Receiver)
□ Gain adjustments
▶ 3-Knob TGC control
Slider bar TGC와 3-knob TGC비교

24. compensate(Receiver)
□ Gain adjustments
▶ Internal time-varied gain
: automatically set swept gain
▶ Lateral gain
Lateral 반사파의 모양이 원형인 경우 거리에 따라 보상

25. compensate(Receiver)
□ Dynamic frequency tuning
▶ Higher frequency sound waves are attenuated more rapidly and
penetrate less deeply than lower frequencies.
고주파수 성분은 깊게 침투할수록 attenuation이 심해져서 사라지게 되고 저주파수 성분만 남게 됨

26. compensate(Receiver)
□ Dynamic frequency tuning
▶ Higher frequency sound waves are attenuated more rapidly and
penetrate less deeply than lower frequencies.
▶ shallow regions  higher frequencies
deeper regions  lower frequencies

27. Dynamic range and compression(Receiver)
▶ Limited input signal amplitude range to respond effectively
▶ Threshold < Input signal < Saturation

28. Dynamic range and compression(Receiver)
□ Log compression
▶ Receiver : 100~120dB Memory : 40~45dB
Monitor(contrast) : 20~30dB
Log Compression

29. Dynamic range and compression(Receiver)
□ Log compression
신호의 amplitude가 조금만 변해도 log compression을 하게 되면 크기의 변화가 커지게 되므로
log compression을 하게 되면 명암이 더 커짐
▶ Low dynamic range : High contrast
High dynamic range : Low contrast

30. demodulation(Receiver)
▶ Convert the amplified echo signal into a single pulse
Input signal → rectification → smoothing

31. Reject(Receiver) □ Reject
▶ reject eliminates both low level electronic noise
and low level echoes

32. Reject(Receiver) □ Reject ▶ Adaptive threshold processing
Threshold 를 변화시켜 가며 적용하여 noise또는 작은 amplitude의 echo signal을 제거

33. Ultrasound scanning □ A – mode(amplitude mode)
▶ shows echo amplitude versus reflector distance
▶ only presents echo data from a single beam line(limited uses)
Echo signal의 amplitude와 distance를 표현

34. Ultrasound scanning □ A – mode(amplitude mode)
▶ shows echo amplitude versus reflector distance
▶ only presents echo data from a single beam line(limited uses)
▶ ophthalmological applications
안과학에 응용

35. Ultrasound scanning □ B – mode(brightness mode)
▶ echo signals are converted to intensity-modulated dots
▶ brightness ∝ echo signal amplitude
Echo signal이 클수록 점의 밝기가 커짐

36. Ultrasound scanning
A모드와 B모드의 비교
A - mode
B - mode

37. Ultrasound scanning □ M – mode(motion mode)
▶ by slowly sweeping a B-mode trace across a screen
▶ depth on one axis and time on an orthogonal axis
B모드를 화면에 지나가면서 나타냄
가로축은 시간 세로축은 깊이

38. Ultrasound scanning ∆d ∆t □ M – mode(motion mode)
▶ velocity of a reflector is estimated from
가로축의 시간과 세로축의 거리로 움직이는 reflector의 움직임의 평균속도를 구할 수 있음 ∆d ∆t

39. Ultrasound b-mode scanning
□ Image build-up
▶ called 2-D image
▶ echoes are positioned along a line that
corresponds to the beam axis
B 모드를 이용하여 여려 방향에서 얻은 정보를 모아 하나의 화면에 나타내어 2-D image를 얻을 수 있음

40. scanners □ Linear array transducers
▶ small rectangular elements lined up side by side
▶ parallel beam line
작은 element를 옆으로 붙인 것이 linear array
평행한 빔으로 반향 정보를 얻어냄

41. scanners □ Linear array transducers
▶ small rectangular elements lined up side by side
뼈(acoustic impedance가 매우 큼)는 잘 통과하지 못함

42. scanners □ Convex array transducers
▶ same principles as a linear array
▶ beam lines are not parallel, emerge at different angles
Convex array는 곡면으로 이루어진 probe entrance window에 element배열
따라서 빔 라인은 평행하지 않고 다른 각으로 퍼져나감

43. scanners □ Convex array transducers
▶ larger imaged field than linear array
넓은 범위를 볼 수 있어 복부 등 넓은 범위에 응용

44. scanners □ Phased array transducers
▶ electronically steered at various angles
▶ electronic focusing
Transmit pulse에 delay를 다르게 주어 beam steering 가능
Beam steering과 focusing 모두 적용 가능

45. scanners □ Phased array transducers
▶ through the intercostal (small entrance window)
▶ cardiac imaging
뼈는 초음파가 잘 통과하지 못함
Window entrance가 작은 phased array는 늑골사이로 빔을 쏘아
Steering하여 늑골 안의 모습을 관찰할 수 있음

46. scanners □ Mechanical scan
▶ two to four separate transducers positioned
in different locations on the rim of rotating wheel
성인 심장의 동맥 속
하얀 화살표 관상 동맥 혈전(심장발작)

47. Frame rate and scanning speed limitations
□ Maximum frame rate
▶ D : depth
C : speed of sound in tissue (1540 m/s)
N : the number of lines

48. Frame rate and scanning speed limitations
□ Maximum frame rate
▶ D : depth
C : speed of sound in tissue (1540 m/s)
N : the number of lines
D ↑ ⇒ Frame Rate↓
N↑ ⇒ Frame Rate↓
N↑ ⇒ Frame Rate↓
Smaller image size
Resolution 유지