PulseEcho Ultrasound Pulsing Characteristics and Duty Factor Instrumentation
- Slides: 48
▣ 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
□ The Range Equation □ T : Pulse Echo travel time □ c : speed of ultrasound in target material
□ Pulse Duration↓ ⇒ Axial resolution↑ □ Pulse repetition period : Wait for Echo pulse PP↑ ⇒ frame rate ↓ □ Duty Factor
□ 구현 방식 ▶ Analog vs Digital □ Beam steering and focusing (pulse delay sequence) ▶ transmit focusing ▶ dynamic focusing of received echo ▶ controls the beam direction
□ 구현 방식 ▶ Digital ① Stable : external factor (ex. temperature) ② programmability ③ wide range of signal frequency
□ Beam steering and focusing (pulse delay sequence) ▶ transmit focusing ▶ dynamic focusing of received echo ▶ controls the beam direction different time delay array transmitter focusing Transmit focusing
□ Beam steering and focusing (pulse delay sequence) ▶ transmit focusing ▶ dynamic focusing of received echo ▶ controls the beam direction array different time delay transducer same delayed signal focused signal reflector Dynamic focusing of received echo
□ Beam steering and focusing (pulse delay sequence) ▶ transmit focusing ▶ dynamic focusing of received echo ▶ controls the beam direction Controls the beam direction
□ 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↑
□ Pulse transmitter ▶ provide electrical signals for exciting transducer Low output power (MI is 0. 2) High output power (MI is 0. 8)
□ Procedure of the receiver
□ Preamplifier Boosts echo signals protect the receiver from high-voltage □ problem : amplify noise
□ Gain adjustments ▶ Overall gain control : Increase amplification at all depths Low gain High gain
□ Gain adjustments ▶ Overall gain control : Increase amplification at all depths Low gain High gain
□ Gain adjustments ▶ Swept gain or TGC(time gain compensation) : Attenuation compensation depending depth
□ Gain adjustments ▶ Swept gain or TGC ▶ Slider bar TGC control
□ Gain adjustments ▶ 3 -Knob TGC control
□ Gain adjustments ▶ Internal time-varied gain : automatically set swept gain ▶ Lateral gain
□ Dynamic frequency tuning ▶ Higher frequency sound waves are attenuated more rapidly and penetrate less deeply than lower frequencies.
□ 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
□ Dynamic range ▶ Limited input signal amplitude range to respond effectively ▶ Threshold < Input signal < Saturation
□ Log compression ▶ Receiver : 100~120 d. B Memory : 40~45 d. B Monitor(contrast) : 20~30 d. B Log Compression
□ Log compression ▶ Low dynamic range : High contrast High dynamic range : Low contrast
□ Demodulation ▶ Convert the amplified echo signal into a single pulse Input signal → rectification → smoothing
□ Reject ▶ reject eliminates both low level electronic noise and low level echoes
□ Reject ▶ Adaptive threshold processing
□ A – mode(amplitude mode) ▶ shows echo amplitude versus reflector distance ▶ only presents echo data from a single beam line(limited uses)
□ A – mode(amplitude mode) ▶ shows echo amplitude versus reflector distance ▶ only presents echo data from a single beam line(limited uses) ▶ ophthalmological applications
□ B – mode(brightness mode) ▶ echo signals are converted to intensity-modulated dots ▶ brightness ∝ echo signal amplitude
A - mode B - mode
□ M – mode(motion mode) ▶ by slowly sweeping a B-mode trace across a screen ▶ depth on one axis and time on an orthogonal axis
□ M – mode(motion mode) ▶ velocity of a reflector is estimated from ∆d ∆t
□ Image build-up ▶ called 2 -D image ▶ echoes are positioned along a line that corresponds to the beam axis
□ Linear array transducers ▶ small rectangular elements lined up side by side ▶ parallel beam line
□ Linear array transducers ▶ small rectangular elements lined up side by side
□ Convex array transducers ▶ same principles as a linear array ▶ beam lines are not parallel, emerge at different angles
□ Convex array transducers ▶ larger imaged field than linear array
□ Phased array transducers ▶ electronically steered at various angles ▶ electronic focusing
□ Phased array transducers ▶ through the intercostal (small entrance window) ▶ cardiac imaging
□ Mechanical scan ▶ two to four separate transducers positioned in different locations on the rim of rotating wheel
□ Maximum frame rate ▶ D : depth C : speed of sound in tissue (1540 m/s) N : the number of lines
□ 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 유지
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