Optimisation of Image Acquisition Bordeaux 16th November 2016 J.S. McGhie W.B. Vletter R. Frowijn No disclosures
Image optimisation: The Echo machine It looks difficult to drive an echo machine!!
Some things never change they just look better 1975 2016 Current machines control much of the image and signal processing
Image optimisation: Echocardiographic machine capable of: - 2D imaging, M-mode - pulsed & continuous wave Doppler - colour flow Doppler mapping - electrocardiogram - analysis software - optional: tissue doppler analysis, 3D echocardiography. Machine operator: - fully trained,dedicated,sonographer,physicians - continuing education credits
Image optimisation: Knobology Echo machine controls can be grouped according to application: - Imaging Controls - Spectral Doppler Controls - Colour Flow Mapping Controls - Display, Measurement and Recording - Set Up Differences exist in manufactures with respect to how much OPERATOR control is allowed.
Image optimisation: The Echo machine Monitor: Adjust the contrast and brightness so that both the weakest and strongest gray levels are present on the screen System preset: Standard for your lab to produce uniform appereance of studies. A MUST in colour Doppler maps ie33
Image optimisation Gain iscan Depth Focus TGC
Image optimisation
Image optimisation: Technical skill Patient position - left (right) lateral decubitus position supine position Selection of the transducer Higher frequency: Better resolution less penetration (pediatric) Lower frequency: Poorer resolution better penetration (adult) Transducer position - Minor adjustment of transducer position can provide a better acoustic window. - Consider contact between transducer tip and skin Focus
Image optimisation: Selection of the transducer Fundamental S12-4 Best spatial resolution Most impaired penetration 2 nd Harm. 1.3 2.6Mhz Impaired spatial resolution Most possible penetration The worse the acoustic window the lower the frequency
Image optimisation: Technical skill Patient position - left (right) lateral decubitus position supine position Selection of the transducer Higher frequency: Better resolution less penetration (pediatric) Lower frequency: Poorer resolution better penetration (adult) Transducer position - Consider contact between transducer tip and skin - Minor adjustment of transducer position can provide a better acoustic window. Focus
Image optimisation: Transducer position
Image optimisation: Transducer position
Image optimisation: Focus To optimize resolution at a specific distance Structures proximal to the focus level are better visualized
Image optimisation: Gain settings Gain setting Overall gain Adjusts the amplitude of the received signals over the total length of the ultrasound beam. Time-gain compensation Allows differential adjustments along this length to compensate for the effect of attenuation Compression The amplitude range of the reflected signal is compressed into a range of values from white to black
Image optimisation: Gain setting Correct gain setting Overall gain Time gain compensation (TGC)
Image optimisation: Compression Gainsetting Overall gain Adjusts the amplitude of the received signals over the total length of the ultrasound beam. Time-gain compensation Allows differential adjustments along this length to compensate for the effect of attenuation Compression The amplitude range of the reflected signal is compressed into a range of values from white to black
Image optimisation: Compression Compress 30 Gain 62% Compress 40 Gain 62% Compress 50 Gain 62% Compress 60 Gain 62% To provide an image with a gradation of gray levels the number of levels of gray can be adjusted by the compress / dynamic range setting Default setting 50 55 (ie 33)
Image optimisation: Tissue Harmonic Imaging Tissue Harmonic Imaging In tissue harmonic imaging the harmonic frequency energy is generated as the ultrasonic wave propagates through the tissue By processing the received signals the second harmonic is filtered out and displayed Framerate Number of images per second depends on the number of scan lines and adjusted depth (routine setting 40 frames per second)
Image optimisation: Fundamental 2 nd Harmonic Fundamental (FR 75Hz) Gain 44% 2 nd Harm. 1.7 3.4Mhz (FR 64Hz) Gain 62% Harmonic imaging improves signal-to-noise-ratio. Better lateral resolution poorer axial resolution
Image optimisation: Fundamental 2 nd Harmonic Important The type of processing required to filter out the received harmonic signal does make structures within the heart appear slightly thicker in harmonic as compared with fundamental frequency
Image optimisation: 2 nd Harmonic - XRES
Image optimisation: Framerate Tissue Harmonic Imaging In tissue harmonic imaging the harmonic frequency energy is generated as the ultrasonic wave propagates through the tissue By processing the received signals the second harmonic is filtered out and displayed Framerate Number of images per second depends on the adjusted depth, sector angle and number of scan lines. (routine setting 40 frames per second)
Image optimisation: Framerate Begin with sufficient depth to see beyond the heart Reduce depth till area of interest fills the screen Depth 19cm = FR 50Hz Depth 13cm = FR 55Hz
Image optimisation: Framerate Decrease sector angle Decrease line density Depth 13cm = FR 72Hz (speckle tracking) Depth 13cm = FR 88Hz
Image optimisation: Framerate X5-1 matrix transducer Matrix array technology utilizes 2400 fully-sampled elements for 360-degree focusing and steering xplane
Image optimisation: Framerate Frame rate 74Hz Frame rate 37Hz xplane lateral tilt +30 (+45 ) -30 (-45 )
Image optimisation: Framerate ROI: LV (VR 33HZ) ROI: LA (VR 51HZ)
Color Doppler Flow Imaging Gain Setting Adjusts the degree of amplification of received Doppler signals To optimize the flowsignal the gain setting is just below the level of random background noise Framerate + Velocity range Sector depth Sector width Line density Pulse repetition frequency (PRF)
Color Doppler Flow Imaging: 2D gain Reduce 2D gain! Color flow data is not displayed on the top of structures (including noise due to excessive gain)
Color Doppler Flow Imaging: Color gain setting Radom noise Correct gain setting Too low gain = diminished sensitivity (large jets appear smaller)
Color Doppler Flow Imaging: FR sector size Frame rate 8 Hz Frame rate 21 Hz Increased sector width requires more scan lines resulting in slower frame rate So keep color area to a minimum
Color Doppler Flow Imaging: FR sector size Frame rate 22Hz xplane lateral tilt Frame rate 11Hz +30 (+45 ) -30 (-45 )
Color Doppler Flow Imaging: FR sector depth FR 17 Hz FR 17 Hz FR 29 Hz Same transmit-receiving time No difference in frame rates Less transmit-receiving time Higher frame rate
Color Doppler Flow Imaging: Velocity range VR 91 cm/s VR 61 cm/s VR 30 cm/s Default setting velocity scale 60 cm/s
Color Doppler Flow Imaging: Velocity range(tcpc) Low PRF setting use a low wall filter, therefore low velocity flow is visible
Spectral Doppler modes Continuous Wave (CW) No upper velocity limit but No depth discrimination Pulsed Wave (PW) Upper velocity limited by Aliasing but Does provide spatial location
Pulsed Wave Doppler: Sample volume position
Standard settings pulsed/ continuous wave Doppler Filter setting Baseline shift High pass filters eliminate low frequency Doppler shifts Use Baseline shift to maximise Velocity Scale Velocity range Gain setting Optimize for precise velocity measurements Too high gain setting overrate velocity measurements
Continuous Wave Doppler: Gain setting Vmax 3.2 m/s Max PG 41 mmhg Mean PG 24 mmhg VTI 83 cm Vmax 3.5 m/s Max PG 50 mmhg Mean PG 29 mmhg VTI 94 cm
Pulsed Wave Doppler: Gain setting CWD Aortic valve PWD LVOT correct gain setting higher gain setting PG 82 mmhg VTI 96.1 cm (LVOT 17 mm) VTI 36.5 cm AVA 0.86 cm 2 VTI 44.3 cm AVA 1.04 cm 2
Ultrasound Image Artifacts Definition: False, multiple or misleading information introduced by the imaging system or by interaction of ultrasound with the adjacent tissue Can be falsely interpreted as real pathology May obscure pathology Important to understand and appreciate
Ultrasound Image Artifacts Do not believe everything you see
Ultrasound Image Artifacts Acoustic enhancement Acoustic shadowing Wide beam artifact Side lobe artifact Reverberation artifact Gain artifact Contact artifact
Image Artifacts: Reverberation This causes evenly spaced lines at increasing depths Sound reflects back and forth between the surface of the probe and a strong reflector close to the surface Bron: A.Pally
Image Artifacts: Reverberation TTE TTE
Image Artifacts: Side Lobe The probe cannot produce a pulse that travels purely in one direction
Image Artifacts: Acoustic shadowing Occurs distal to any highly reflective or highly attenuating surface Failure to visualize the source of a shadow is usually caused by the object being outside the plane of the ultrasound beam Bron: A.Pally
Image Artifacts: Refraction X Sound is refracted as it passes from one medium to another. Thus the direction in which it travels changes, when the angle is < 90 this can lead to: subtle miss placement of structures degeneration of image quality Bron: A.Pally
Image Artifacts: Refraction Ghost Image A dramatic example of refraction. A structure is represented twice or more, side by side
Image optimisation: Take Home Message Important - use all modalities of the echocardiographic techniques Settings have to be - optimized for each individual patient - adjusted with respect to the target lesions that have to be analysed Artifacts - change the transducer position - change the angulation of the transducer WRONG SETTINGS! Important findings will not be documented and can also be overlooked
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