Characterization of elastographic noise using the envelope of echo signals.

A theoretical formulation characterizing the noise performance of strain estimation using envelope signals is presented for the cross-correlation based strain estimator in elastography, using a modified strain filter approach. The strain filter describes the relationship among the elastographic signal-to-noise ratio (SNRe), sensitivity, contrast-to-noise ratio and dynamic range for a given resolution in the elastogram, as determined by the cross-correlation window length and window overlap. Theoretical results indicate that the envelope strain filter noise performance (SNRe level) is about half that obtained in the ratio frequency (RF) case (fo = 7.5 MHz). Simulation results corroborate the trend predicted using the strain filter. Experimental SNRe vs. strain plots presented in this article illustrate the same trend as the theoretical results. These plots allow a quantitative comparison of the elastograms obtained with RF and envelope signal processing. For small strains, the performance obtained using RF signals is superior to that obtained for envelope signals (since jitter errors are smaller due to the utilization of phase information in RF signals). However, for large tissue strains, envelope analysis provides an accurate estimate of the tissue strain (since envelope signal decorrelation is smaller than RF signal decorrelation at large strains). An algorithm that combines the low-noise characteristics of the cross-correlation analysis using RF signals at small strains and envelope signals for estimation of large tissue strains is proposed to improve the dynamic range in the elastogram.

[1]  T. Krouskop,et al.  Phantom materials for elastography , 1997, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[2]  G E Trahey,et al.  Potential and limitations of angle-independent flow detection algorithms using radio-frequency and detected echo signals. , 1991, Ultrasonic imaging.

[3]  J. Ophir,et al.  Reduction of signal decorrelation from mechanical compression of tissues by temporal stretching: applications to elastography. , 1997, Ultrasound in medicine & biology.

[4]  J Ophir,et al.  On the use of envelope and RF signal decorrelation as tissue strain estimators. , 1997, Ultrasound in medicine & biology.

[5]  M. Bilgen,et al.  Deformation models and correlation analysis in elastography. , 1996, The Journal of the Acoustical Society of America.

[6]  L. Wilson,et al.  Ultrasonic measurement of small displacements and deformations of tissue. , 1982, Ultrasonic imaging.

[7]  J. Ophir,et al.  Theoretical bounds on strain estimation in elastography , 1995, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[8]  Y. Yamakoshi,et al.  Ultrasonic imaging of internal vibration of soft tissue under forced vibration , 1990, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[9]  M. O’Donnell,et al.  Internal displacement and strain imaging using ultrasonic speckle tracking , 1994, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[10]  T. Varghese,et al.  Enhancement of echo-signal correlation in elastography using temporal stretching , 1997, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[11]  J Ophir,et al.  The nonstationary strain filter in elastography: Part II. Lateral and elevational decorrelation. , 1997, Ultrasound in medicine & biology.

[12]  G. Trahey,et al.  Potential and Limitations of Angle-Independent Flow Detection Algorithms Using Radio-Frequency and Detected Echo Signals , 1991 .

[13]  F. Kallel,et al.  Elastography: A systems approach , 1997, Int. J. Imaging Syst. Technol..

[14]  J.R. Crowe,et al.  Displacement and strain imaging of coronary arteries with intraluminal ultrasound , 1996, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[15]  A. Weiss,et al.  Fundamental limitations in passive time delay estimation--Part I: Narrow-band systems , 1983 .

[16]  P L Carson,et al.  Ultrasound tissue displacement imaging with application to breast cancer. , 1995, Ultrasound in medicine & biology.

[17]  M. Bilgen,et al.  Error analysis in acoustic elastography. II. Strain estimation and SNR analysis. , 1997, The Journal of the Acoustical Society of America.

[18]  E. Feleppa,et al.  Relationship of Ultrasonic Spectral Parameters to Features of Tissue Microstructure , 1987, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[19]  Nigel L. Bush,et al.  Freehand Elasticity Imaging Using Speckle Decorrelation Rate , 1996 .

[20]  T. Varghese,et al.  Multiresolution imaging in elastography , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[21]  C T Lancée,et al.  Intravascular elasticity imaging using ultrasound: feasibility studies in phantoms. , 1997, Ultrasound in medicine & biology.

[22]  J. Meunier,et al.  Ultrasonic biomechanical strain gauge based on speckle tracking , 1989, Proceedings., IEEE Ultrasonics Symposium,.

[23]  J. Ophir,et al.  Reduction of Image Noise in Elastography , 1993 .

[24]  L. Wilson,et al.  Spectral tissue strain: a new technique for imaging tissue strain using intravascular ultrasound. , 1994, Ultrasound in medicine & biology.

[25]  G. Carter.  Coherence and time delay estimation , 1987, Proceedings of the IEEE.

[26]  Variable Compressions with RF and Baseband Processing for Dynamic Range Expansion of Elastograms , 1997 .

[27]  J. Ophir,et al.  An adaptive strain estimator for elastography , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[28]  T. Varghese,et al.  A theoretical framework for performance characterization of elastography: the strain filter , 1997, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[29]  B. Garra,et al.  Elastography of breast lesions: initial clinical results. , 1997, Radiology.

[30]  M. Doyley,et al.  Strain imaging using combined RF and envelope autocorrelation processing , 1996, 1996 IEEE Ultrasonics Symposium. Proceedings.

[31]  W. Walker,et al.  A fundamental limit on delay estimation using partially correlated speckle signals , 1995, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[32]  B. Garra,et al.  Elastography: Ultrasonic imaging of tissue strain and elastic modulus in vivo , 1996 .

[33]  K J Parker,et al.  Tissue response to mechanical vibrations for "sonoelasticity imaging". , 1990, Ultrasound in medicine & biology.

[34]  M. O’Donnell,et al.  Measurement of arterial wall motion using Fourier based speckle tracking algorithms , 1991, IEEE 1991 Ultrasonics Symposium,.

[35]  R. F. Wagner,et al.  Statistics of Speckle in Ultrasound B-Scans , 1983, IEEE Transactions on Sonics and Ultrasonics.

[36]  K J Parker,et al.  Imaging of the elastic properties of tissue--a review. , 1996, Ultrasound in medicine & biology.

[37]  J Ophir,et al.  The nonstationary strain filter in elastography: Part I. Frequency dependent attenuation. , 1997, Ultrasound in medicine & biology.

[38]  A. Manduca,et al.  Magnetic resonance elastography by direct visualization of propagating acoustic strain waves. , 1995, Science.

[39]  J. Ophir,et al.  The combined effect of signal decorrelation and random noise on the variance of time delay estimation , 1997, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[40]  J. Ophir,et al.  Elastography: A Quantitative Method for Imaging the Elasticity of Biological Tissues , 1991, Ultrasonic imaging.

[41]  J. Bendat,et al.  Random Data: Analysis and Measurement Procedures , 1987 .