0507-0815-Patil-Concepts of Imaging and Knobology · –As ultrasound travels through tissue energy...
Transcript of 0507-0815-Patil-Concepts of Imaging and Knobology · –As ultrasound travels through tissue energy...
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Concepts of Imaging and Knobology
Pravin Patil, MD FACC FASEAssociate Professor of Medicine
Director, Cardiovascular Disease Training ProgramLewis Katz School of Medicine at Temple University
Disclosures No relevant financial disclosures
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EchocardiographyTomographic Imaging
– Echo is a “thin slice” imaging tool like cardiac CT, MRI and nuclear imaging– However, images are not automatically acquired– Achieved by probe manipulation, acoustic windows, patient positioning, balancing of artifacts and image processing
The ability to optimize the image acquisition and processing is part of competency in echocardiography
“Knobology”
Source: Philips, GE, Siemens, Esaote, Toshiba
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Ultrasound Probe
Source: WikiRadiography.netPhased Array
Garbi, M. The EAE Textbook of Echocardiography 2011
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Machines and Knobs
Gain
Comp
DepthFocus
Zoom
LGC
TGC
AutoGain
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GainComp Depth
Zoom
LGC
TGC
AutoGain
Focus
`
Gain
Comp
Depth
Zoom
TGC
AutoGain
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Rise of the Touchscreen and Trackpad
Source: Philips Healthcare, GE Healthcare
Echo Screen Anatomy
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Echo Screen Anatomy
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Frame Rate
Temporal Resolution– Limited by line density and time to scan– Improves with narrow sector width– Unless line density decreases
Appearance– FR <15 Hz appear choppy– FR >15 Hz appear smooth
Echo Screen Anatomy
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Imaging Depth Imaging Depth
– Start with larger than needed– Adjust to place ROI approximately ¾– Leave small area behind to observe useful artifacts like shadowing
Depth
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Depth
LPE20 cm Depth
12 cm Depth
Echo Screen Anatomy
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Frequency
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Axial Resolution × Frequency
Zoom
Larger Pixels, Higher Frame RateNot Higher Axial Resolution
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Harmonic Imaging Improves signal-to-noise ratio
Contrast– Non-linear resonance of bubbles to compressions and rarefactions
of ultrasound wave
Tissue (incidental discovery)– Related to propagation of sound through the myocardium– Non-linear response due to higher speed during compression than
in rarefaction.McCulloch, et al. JASE 2000
Tissue Harmonic Imaging
f 2f
Sign
al Amplitude
Tissue Noise
Non-linear distortion of acoustic signal in tissue generates harmonics
Noise/artifacts generate no significant harmonic
Tissue Harmonic Imaging takes advantage of increased SNR
SNR 1.5
SNR 3
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Fundamental Second HarmonicGarbi, M. The EAE Textbook of Echocardiography 2011
Tissue Harmonic Imaging
Fundamental Tissue Harmonic
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Tissue Harmonic Imaging
Bubbles Have Harmonics too..
Harmonics 1.3/2.6 MHz Fundamental 1.6 MHz
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Echo Screen Anatomy
Lateral Resolution
Focal Zone / Focus
Increased ability to discern two separate objects at the FZ
Apical Wall Motion Abnormality, Concern for LV thrombus
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Echo Screen Anatomy
Gain Compression
Adapted from Garbi, M. The EAE Textbook of Echocardiography 2011
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Auto Gain
Decrease
2D Gain
DopplerGain
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Time Gain Compensation (TGC)
Lateral Gain Compensation (LGC)
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Compression
Color
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Human Grayscale
Humans perceive approximately 30 shades of gray
Cones are high bandwidth and allow humans to see at least 10 million shades of color
Echo Screen Anatomy
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Ultrasound BioeffectsUltrasound is mechanical energy
– Thermal effects– Mechanical effects
Background– No evidence that diagnostic ultrasound produces harm– Subtle or transient effects not well understood
ALARA– As Low As Reasonably Achievable
Mechanical Index (MI)Quantification of US acoustic intensity
MI = P(Pascals)/√Frequency(MHz)
Non-thermal (Mechanical) Bioeffects– MI expresses the acoustic pressure of US beam on insonated structures
Lower MI induces increased bubble resonance and harmonics
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Low MI Example
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Thermal Index (TI)
Quantification of potential for tissue heating– As ultrasound travels through tissue energy is absorbed by tissue and converted to heat– Frequency and intensity dependent
Recommendation is to keep tissue heating < 1.5 °C– Caution with the febrile patient
Thermal Bioeffects
Doppler EchocardiographyOptimal 2D images when ultrasound beam is
perpendicular to structures
Optimal Doppler imaging when ultrasound beam is parallel to flow
Apical views allow alignment with most cardiac flows (i.e. aortic, mitral and tricuspid valves)
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Doppler Echocardiography Color Flow Doppler
– Pulse wave modality that cannot resolve high velocities
– Turbulence/variance maps can help define jet, direction and turbulence
Pulse Wave Spectral Doppler– Range specific– Subject to aliasing at high velocities like CFD
Continuous Wave Spectral Doppler– Able to resolve high velocities– Range ambiguous
Color Flow Doppler Pay attention to the baseline Make note of the Nyquist limit Color scales vary Variance maps (see example) Optimize size of box and sector
for frame rate
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Variance Map
s/p Mitral ViVS3 26 mm
Spectral Doppler Scale
Scale Optimized
Too Small Too Large
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Spectral Doppler Baseline
Baseline Adjusted
Doppler Gain
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Doppler Gain
Nyquist Limit
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Doppler Sweep
150 mm/s75 mm/s
ASCeXAM Focus Image optimization “Knobology” is part of achieving competency in echocardiography
Key components of image optimization 2D Gain
Compression
Mechanical index
Harmonic Imaging
Frame Rate
Resolution
Depth
Doppler Gain
Doppler Sweep/Scale
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Thank You!