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Pulse-Echo Ultrasound Pulsing Characteristics and Duty Factor Instrumentation Beam former Pulse Transmitter Receiver Ultrasound scanning Scanners Linear.

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Presentation on theme: "Pulse-Echo Ultrasound Pulsing Characteristics and Duty Factor Instrumentation Beam former Pulse Transmitter Receiver Ultrasound scanning Scanners Linear."— Presentation transcript:

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2 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 The Range Equation T : Pulse Echo travel time c : speed of ultrasound in target material

4 Pulse Duration Pulse Duration Axial resolution Pulse repetition period : Wait for Echo pulse PP frame rate Duty Factor

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7 Analog vs Digital Beam steering and focusing (pulse delay sequence) transmit focusing dynamic focusing of received echo controls the beam direction

8 Analog 20~40ns focusing

9 Digital Stable : external factor (ex. temperature) programmability wide range of signal frequency

10 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 steering and focusing (pulse delay sequence) transmit focusing dynamic focusing of received echo controls the beam direction Dynamic focusing of received echo

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

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14 Pulse transmitter provide electrical signals for exciting transducer Transmit power Higher intensity sound wave Higher amplitude echo signal Appear brighter and weaker reflectors In the display But acoustical exposure to the patient

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

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17 Procedure of the receiver

18 Preamplifier Boosts echo signals protect the receiver from high-voltage problem : amplify noise

19 Gain adjustments Overall gain control : Increase amplification at all depths High gain Low gain

20 Gain adjustments Overall gain control : Increase amplification at all depths High gain Low gain

21 Gain adjustments Swept gain or TGC(time gain compensation) : Attenuation compensation depending depth

22 Gain adjustments Swept gain or TGC Slider bar TGC control

23 Gain adjustments 3-Knob TGC control

24 Gain adjustments Internal time-varied gain : automatically set swept gain Lateral gain

25 Dynamic frequency tuning Higher frequency sound waves are attenuated more rapidly and penetrate less deeply than lower frequencies.

26 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 Limited input signal amplitude range to respond effectively Threshold < Input signal < Saturation

28 Log compression Receiver : 100~120dB Memory : 40~45dB Monitor(contrast) : 20~30dB Log Compression

29 Log compression Low dynamic range : High contrast High dynamic range : Low contrast

30 Demodulation Convert the amplified echo signal into a single pulse Input signal rectification smoothing

31 Reject reject eliminates both low level electronic noise and low level echoes

32 Reject Adaptive threshold processing

33 A – mode(amplitude mode) shows echo amplitude versus reflector distance only presents echo data from a single beam line(limited uses)

34 A – mode(amplitude mode) shows echo amplitude versus reflector distance only presents echo data from a single beam line(limited uses) ophthalmological applications

35 B – mode(brightness mode) echo signals are converted to intensity-modulated dots brightness echo signal amplitude

36 A - mode B - mode

37 M – mode(motion mode) by slowly sweeping a B-mode trace across a screen depth on one axis and time on an orthogonal axis

38 M – mode(motion mode) velocity of a reflector is estimated from t d

39 Image build-up called 2-D image echoes are positioned along a line that corresponds to the beam axis

40 Linear array transducers small rectangular elements lined up side by side parallel beam line

41 Linear array transducers small rectangular elements lined up side by side

42 Convex array transducers same principles as a linear array beam lines are not parallel, emerge at different angles

43 Convex array transducers larger imaged field than linear array

44 Phased array transducers electronically steered at various angles electronic focusing

45 Phased array transducers through the intercostal (small entrance window) cardiac imaging

46 Mechanical scan two to four separate transducers positioned in different locations on the rim of rotating wheel

47 Maximum frame rate D : depth C : speed of sound in tissue (1540 m/s) N : the number of lines

48 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 Smaller image size Resolution


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