Rapid tracking of small displacements with ultrasound

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2006-06, Vol.53 (6), p.1103-1117
• Main Authors: Pinton, G.F., Dahl, J.J., Trahey, G.E.
• Format: Article
• Language: English
• Subjects: Accuracy; Acoustic measurements; Acoustics; Algorithms; Animals; Biological and medical sciences; Blood flow; Cattle; Clustering algorithms; Computer Simulation; Cross correlation; Exact sciences and technology; Fluid flow measurement; Force measurement; Format; Fundamental areas of phenomenology (including applications); General equipment and techniques; Hepatectomy; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Imaging; In Vitro Techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Investigative techniques, diagnostic techniques (general aspects); Liver - diagnostic imaging; Liver - physiology; Liver - surgery; Medical sciences; Miscellaneous. Technology; Models, Biological; Movement - physiology; Phase estimation; Phase measurement; Physics; Scanners; Studies; Transducers; Ultrasonic imaging; Ultrasonic investigative techniques; Ultrasonic variables measurement; Ultrasonics, quantum acoustics, and physical effects of sound; Ultrasonography - methods; Ultrasound; Wavelength measurement
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2006.1642509

Time-delay estimators, such as normalized cross correlation and phase-shift estimation, form the computational basis for elastography, blood flow measurements, and acoustic radiation force impulse (ARFI) imaging. This paper examines the performance of these algorithms for small displacements (less than half the ultrasound pulse wavelength). The effects of noise, bandwidth, stationary echoes, kernel size, downsampling, interpolation, and quadrature demodulation on the accuracy of the time delay estimates are measured in terms of bias and jitter. Particular attention is given to the accuracy and resolution of the displacement measurements and to the computational efficiency of the algorithms. In most cases, Loupas' two-dimensional (2-D) autocorrelator performs as well as the gold standard, normalized cross correlation. However, Loupas' algorithm's calculation time is significantly faster, and it is particularly suited to operate on the signal data format most commonly used in ultrasound scanners. These results are used to implement a real-time ARFI imaging system using a commercial ultrasound scanner and a computer cluster. Images processed with the algorithms are examined in an ex vivo liver ablation study.