Quantifying Cardiac Deformation by strain (-rate) imaging Hans Torp NTNU, Norway Hans Torp...
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Transcript of Quantifying Cardiac Deformation by strain (-rate) imaging Hans Torp NTNU, Norway Hans Torp...
Quantifying Cardiac Deformation by strain (-rate) imaging
Hans TorpNTNU, Norway
Hans Torp Department of Circulation and Medical Imaging
Norwegian University of Science and Technology Norway
Quantifying Cardiac Deformation
by strain (-rate) imaging
• Describe deformation by strain and strain rateDescribe deformation by strain and strain rate
• Ultrasound methods for strain rateUltrasound methods for strain rate– speckle tracking versus Doppler methodsspeckle tracking versus Doppler methods
– Clutter noise and thermal noiseClutter noise and thermal noise
– angle dependencyangle dependency
• Frame rate issuesFrame rate issues
• Visualization of strain and strain-rateVisualization of strain and strain-rate
Hans TorpNTNU, Norway
Velocity gradient – strain rateVelocity gradient – strain rate
V2 – V1L
= Rate of deformation= Strain Rate
V1
V2
Velocity gradient:
L
(Myocardial) velocity gradient is an instantaneous property
Integrated velocity gradientIntegrated velocity gradientversus strainversus strain
”Growth function” Strain = exp{ IVG } - 1
Integrated velocity gradientIntegrated velocity gradientversus strainversus strain
Envelope RF
What is the best velocity What is the best velocity estimator?estimator?
s1 s2Autocorrelation method is optimal(Maximum likelihood estimator)
velocity ~ angle(R)
RF signals IQ signals
x1 x2
R=x1*x2
What is the best velocity What is the best velocity estimator?estimator?
R=x1*x2 v=c/4piT angle(R)
Estimation error is minimumEstimation error is minimumwhen correlation is maximumwhen correlation is maximum
Hans TorpNTNU, Norway
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 106
0
0.5
1
1.5
2
abs(R)
angl
e(R
))
Correlation magnitude
Vel
ocit
y es
tim
ate
Estimate of velocity gradient Estimate of velocity gradient (strain rate)(strain rate)
0 0.005 0.01 0.0150.01
0.015
0.02
0.025
0.03
depth range [mm]
Ve
loci
ty [
m/s
ec]
Linear regression
Weighted Linear regression(Maximunlikelihood)
Simulation experimentSimulation experimentStrain rate estimatorsStrain rate estimators
10 20 30 40 50
0
0.5
1
1.5
Simulation no
Strain rate
Linear regression
Weighted Linear regression(Maximunlikelihood)
Clutter noise
Clutter noiseClutter 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 clutterindependent of tissue velocity
Fundamental and second Fundamental and second harmonic signal separated by harmonic signal separated by
filterfilter
0 1 2 3 4 5x 106
-20
0
20
40
60
80
20 40 60 80 100
50
100
150
200
250
300
350
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450
Fundamental Signal from septumNoise from LV cavity
2. harmonic-500 0 5000
50
100
150
200
250
-10 0 100
50
100
150
200
250
Hans TorpNTNU, Norway
Second Harmonic TDISecond Harmonic TDI
Fundamental, f=1.67MHz
Second harmonic, f=3.33MHz
• Fundamental and Fundamental and second harmonic second harmonic calculated from the calculated from the same data setsame data set
• No significant noise No significant noise differencedifference
• SSecond harmonic econd harmonic TDI TDI gives more aliasing.gives more aliasing.
Second Harmonic SRISecond Harmonic SRI
Fundamental, f=1.67MHz
Second harmonic, f=3.33MHz
• Fundamental and Fundamental and second harmonic second harmonic calculated from the calculated from the same data setsame data set
• Significant noise Significant noise reduction when using reduction when using the second harmonic the second harmonic frequency bandfrequency band
• Aliasing is not a Aliasing is not a problem due to small problem due to small velocity differencesvelocity differences
Frame rate issues in tissue velocity Frame rate issues in tissue velocity and strain rate imaging and strain rate imaging
Packet Packet acquisitionacquisition
30 - 80 frames/sec30 - 80 frames/sec
Packet acquisitionPacket acquisition
tissue interleavingtissue interleaving
100 - 150 100 - 150 frames/secframes/sec
Continuous Continuous acquisition tissue acquisition tissue interleavinginterleaving
250 - 350 frames/sec250 - 350 frames/sec
- TVI aliasing- TVI aliasing
+ Offline spectral + Offline spectral DopplerDoppler
(Work in progress)(Work in progress)
Image sector: 70 deg.Parallell beams : 2
Packet acquisition - continuous acquisitionPacket acquisition - continuous acquisition
Myocardial velocity and strain rateMyocardial velocity and strain ratewith 300 frames/secwith 300 frames/sec
Velocity
v1
v2
Strain rate
TimeHans TarpNTNU, Norway
Lateral movementLateral movement
Angle corrected strainAngle corrected strain
Summary 1Summary 1
• Strain rate from Tissue Doppler is possible for motion Strain rate from Tissue Doppler is possible for motion along the ultrasound beam with high temporal along the ultrasound beam with high temporal resolutionresolution
• Weighted linear regression gives minimum estimation Weighted linear regression gives minimum estimation errorerror
• Second harmonic Tissue Doppler reduce clutter noise Second harmonic Tissue Doppler reduce clutter noise artefacts in strain rate imagingartefacts in strain rate imaging
Summary 2Summary 2• Integrated strain is improved by Integrated strain is improved by
tracking material pointstracking material points
• 2D speckle-tracking gives angle-2D speckle-tracking gives angle-independent strain, with reduced independent strain, with reduced temporal resolution temporal resolution
• A combination of high frame rate A combination of high frame rate tissue Doppler and lower frame rate tissue Doppler and lower frame rate speckle tracking is probably the best speckle tracking is probably the best solution for strain imagingsolution for strain imaging
• 3D reconstruction of strain (-rate) 3D reconstruction of strain (-rate) covering the left ventricle can be covering the left ventricle can be obtained from 3 standard apical viewsobtained from 3 standard apical views