Quantifying%20Cardiac%20Deformation%20by%20strain%20(-rate)%20imaging

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Quantifying Cardiac Deformation by strain
(-rate) imaging
Hans Torp Department of Circulation and Medical
Imaging Norwegian University of Science and
Technology Norway
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Quantifying Cardiac Deformation by strain
(-rate) imaging

• Describe deformation by strain and strain rate
• Ultrasound methods for strain rate
• speckle tracking versus Doppler methods
• Clutter noise and thermal noise
• angle dependency
• Frame rate issues
• Visualization of strain and strain-rate

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(No Transcript)
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Velocity gradient strain rate
V2 V1 L
Velocity gradient
Rate of deformation Strain Rate
V2
L
V1
(Myocardial) velocity gradient is an
instantaneous property
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Integrated velocity gradientversus strain
Growth function Strain exp IVG - 1
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Integrated velocity gradientversus strain
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Envelope
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What is the best velocity estimator?
velocity angle(R)
Rx1?x2
s2
x2
s1
x1
Autocorrelation method is optimal (Maximum
likelihood estimator)
RF signals
IQ signals
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What is the best velocity estimator?
vc/4piT angle(R)
Rx1?x2
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Estimation error is minimumwhen correlation is
maximum
Velocity estimate
Correlation magnitude
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Estimate of velocity gradient (strain rate)
0.03
0.025
0.02
Velocity m/sec
0.015
0.01
0
0.005
0.01
0.015
depth range mm
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Simulation experimentStrain rate estimators
Linear regression
Strain rate
Weighted Linear regression (Maximun likelihood)
Simulation no
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Clutter noise
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Clutter noise

• bias towards zero for velocity measurements
• increased variance for strain rate

• Clutter filter helps when tissue velocity is high
• limited effect in apical region
• Second harmonic (octave) imaging reduces clutter
• independent of tissue velocity

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Fundamental and second harmonic signal separated
by filter
50
100
150
200
250
300
350
400
450
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40
60
80
100
Fundamental
Signal from septum
Noise from LV cavity
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Second Harmonic TDI
Fundamental, f1.67MHz

• Fundamental and second harmonic calculated from
  the same data set
• No significant noise difference
• Second harmonic TDI gives more aliasing.

Second harmonic, f3.33MHz
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Second Harmonic SRI

• Fundamental and second harmonic calculated from
  the same data set
• Significant noise reduction when using the second
  harmonic frequency band
• Aliasing is not a problem due to small velocity
  differences

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Frame rate issues in tissue velocity and strain
rate imaging

• Packet acquisition
• 30 - 80 frames/sec

Packet acquisition tissue interleaving 100 - 150
frames/sec
Continuous acquisition tissue interleaving 250 -
350 frames/sec - TVI aliasing Offline
spectral Doppler (Work in progress)
Image sector 70 deg. Parallell beams 2
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Packet acquisition - continuous acquisition
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Myocardial velocity and strain ratewith 300
frames/sec
Velocity
Strain rate
Time
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Lateral movement
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Angle corrected strain
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Summary 1

• Strain rate from Tissue Doppler is possible for
  motion along the ultrasound beam with high
  temporal resolution
• Weighted linear regression gives minimum
  estimation error
• Second harmonic Tissue Doppler reduce clutter
  noise artefacts in strain rate imaging

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Summary 2

• Integrated strain is improved by tracking
  material points
• 2D speckle-tracking gives angle-independent
  strain, with reduced temporal resolution
• A combination of high frame rate tissue Doppler
  and lower frame rate speckle tracking is probably
  the best solution for strain imaging
• 3D reconstruction of strain (-rate) covering the
  left ventricle can be obtained from 3 standard
  apical views