Các mode chế độ Siêu Âm (Ultrasound Modes)

Ultrasound Modes Ravi Managuli Simplified Overview Ultrasound System Front-end Transducer Ultrasound Wave ADC Digital Delay Back-end Summer Σ Clinical Signal/Image Processor Display Instrumentation Pulser Switch separates high voltage transmitter from Beamformer low voltage receiver Transmitter Receiver Switch Pre amplification Generates electrical signal Pulser Amplification To compensate depth dependant attenuation Reduce the dynamic range: Equalize larger and smaller echoes Gain/Amplify Swept gain, Gain compensation Compress (dB) : Log compression All signals are amplified uniformly Demodulation Reject Reject Transducer Zoom à write Scan conversion Display lateral a B V2 V4 V3 C vψ-2 V5 vψ-1 Sonographer controllable SC Storage (Memory) ial u ax V1 E D output P(x,y) Called Threshold Low level signals are removed vψ+1 vψ Zoom à Read zoom Receiver Gains !   Two types !   Output power gain and !   Receiver gain Output power   Increases patient exposure   Improves SNR Receiver gain   Amplifies signal uniformly   No change in patient exposure »  Amplifies stronger signal more   Does not change SNR than noise »  ALARA : Be aware »  Signal and noise are treated equally Gain Adjustment TGC !   Compensation à Time gain or Depth gain !   Compensate for the depth dependent attenuation TGC Near gain Delay Depth Slope : Gain compensated Knee : Maximally compensated Far gain : Maximally compensation TGC is only for pulse wave: For CW wave, there is range ambiguity à So TGC cannot be used TGC Adjustment Log Compression !   Log compression !   !   Makes it easy to visualize small level echoes returned from tissues Reduces the dynamic range Scan Converters !   Memory is used to store the data for scan converter !   Also scan converter memory !   Or scan converter itself !   Scan Converter converts data suitable for display !   Coverts polar domain to Cartesian display Scan conversion lateral ax a ial u B C vψ-2 Data stored in memory Performs interpolation to fill the gaps vψ-1 E D output P(x,y) vψ vψ+1 Such interpolation can be used to improve spatial resolution Read vs Write Zoom !   Read magnification !   On the stored data !   Write magnification !   Ultrasound rescans the ROI !   Better spatial resolution Wall Filter !   Amplitude due to clutter (wall motion) !   Is typically 40dB or more (100 times) Amplitude to clutter Amplitude to flow !   !   If not removed, display is littered with clutter !   Difficult to detect Doppler shift due to blood flow Wall motion frequency (velocity) are much lower than Doppler frequency !   Wall filter is used to remove them !   Only Doppler shift is remained After wall filter Wall Filter !   Increasing wall filter !   Decreases low velocity signals !   Flash artifacts !   Decreasing wall filter !   Increases low velocity signals !   For example to visualize end-diastolic velocity Wall filter à No flow seen Decreased wall filter Other Controls for Doppler !   Steer : To steer the Doppler beam !   Doppler angle correct !   To inform the system at what angle the blood vessel is sampled !   Doppler invert !   Reverses positive and negative velocities !   Sweep speed : !   For better visualization of waveform Slow speed Fast speed Fast Speed Wrong Angle Angle Correct Wrong Gain Wrong Gain PRF Setting Wrong PRF PRF Setting Wrong PRF Inside a Commercial Ultrasound Machine Advnaced Applications !   Omni-directional M-mode !   Harmonic Imaging !   B-flow Imaging !   Coded excitation !   Tissue Doppler Imaging !   Tissue Elasticity Imaging !   3D !   BW and Power !   Real-time virual sonography Harmonic Images !   Image created by the reflections that are twice the fundamental !   Non-linear behavior of ultrasound Tissue Harmonic !   Fundamental à many artifact arise in first few centimeters !   Harmonic images are created by deeper structures !   No artifact due to near regions !   The relationship between tissue harmonic and signal strength is non-linear !   Weak signals (side lobe, grating lobe) not create harmonic !   Medium signals (elevation beam) small and !   Strong signal (main beam) create strong harmonics !   Thus artifacts due to grating lobe, side lobes, elevational beams !   Are very small Harmonics Good spatial resolution Less noise Clear boundary and good contrast resolution Wide Pulse Inversion Fundamental Contrast Harmonics : During reflection !   Contrast harmonics are created when ultrasound interacts with a microbubble !   Non linear behavior of microbubbles when sound strikes them !   Tissue harmonics are created during transmission !   Determined by the shell and gas structure !   Mechanical index !   Determines the interaction of microbubbles with ultrasound !   The likelihood of bubble rupture increasing with increasing MI à Causing harmful effect !   MI increases with frequency and high negative pressure !   The peak MI in the focal is estimated by the scanner !   Mechanical index and harmonic creation is non-linear !   < 0.1 MI à No harmonics !   0.1 to 1.0 à Moderate !   > 1.0 à Very strong harmonics à Strong reflection Cavitations Mechanism ! Cavitaion à Bioeffect !   Interaction of sound waves with gas bodies !   Stable !   Occurs at lower MI !   Bubble does not burst !   Transient cavitation à Inertial or normal cavitation !   Occurs at higher MI !   Bubble burst releasing energy !   Not considered clinically significant Ultrasound Technical Trend High Power US (HIFU) Therapy Ultrasound-Enhanced Drug Delivery System Guided by US machine With Treatment Kit （US Guided treatment ） Real-time 3D High Performance US Machine Ultrasound Diagnostic Machine Low Cost US Machine ・Contrast Agent §  Real-time strain image ・Endoscopes BW New Algorithms Portable US machine [...]... Dynamic range and Contrast are user selectable !   By using a different Gray maps provided Diagnostic Ultrasound Machine   Diagnostic imaging modes »  B -mode imaging (B -mode) »  Color flow imaging (BC -mode) »  Spectral Doppler imaging (BCD – mode) Echo signal B -mode processing Scan conversion Transmitter Body Transducer Receiver Receiver & A/D RF demodulator Image processing Color flow signal Color-flow... Ultrasound System - A Mode Control Receiver Time gain compensation |.| Envelop LOG() Reflection strength Depth in tissue Reflection strength compensation Transducer Transmitter Display Depth in tissue Ultrasound System - M Mode Control Receiver Time gain compensation |.| LOG() Depth in tissue Display Depth in tissue compensation Transducer Transmitter Time Ultrasound System - B Mode Control Receiver... V3 V4 V5 compensation Transmitter |.| LOG() Depth in tissue Display Scan conversion lateral V1 V2 V4 V3 a ial V5 ax u B C vψ-2 vψ-1 E D output P(x,y) vψ Depth in tissue vψ+1 Ultrasound : Color Doppler Mode Various Color Images Color Flow Angiograpm or Color Power Doppler Color Doppler Color Flow Variance Image Spectral Doppler Color Flow Image The  Doppler  Shi,   Velocity Determination Depth Transducer... Increasing flow velocity toward the transducer! Zero flow! Increasing flow velocity away from the transducer! Variance Color Map !   Variance color map !   In addition to velocity and direction variance mode distinguishes laminar flow from turbulent flow Turbulent information is also color coded !   Positive direction !   Negative direction Turbulence Velocity Variance Turblance