Impact of propagation through an aberrating medium on the linear effective apodization of a nonlinearly generated second harmonic field

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 53; no. 7; pp. 1260 - 1268
• Main Authors: Wallace, Kirk D., Holland, Mark R., Robinson, Brent S., Fedewa, Russell J., Lloyd, Christopher W., Miller, James G.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-07-2006; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aberration; Acoustics; Algorithms; Animals; Anisotropy; Apodization; Arrays; Beams (radiation); Biological and medical sciences; Computer Simulation; Echocardiography; Echocardiography - methods; Exact sciences and technology; Frequency measurement; Fundamental areas of phenomenology (including applications); General equipment and techniques; Harmonic analysis; Harmonics; Hydrophones; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Image quality; Imaging; In Vitro Techniques; Information Storage and Retrieval - methods; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Investigative techniques, diagnostic techniques (general aspects); Linear Models; Medical sciences; Miscellaneous. Technology; Models, Cardiovascular; Nonlinear Dynamics; Physics; Propagation; Radiation Dosage; Reproducibility of Results; Scattering, Radiation; Sensitivity and Specificity; Sonar equipment; Swine; Transducers; Ultrasonic investigative techniques; Ultrasonic variables measurement; Ultrasonics, quantum acoustics, and physical effects of sound; Human; Echocardiography; Phased array; Harmonic generation; Phase distortion; Image quality; Tissue; Harmonic imaging; Second harmonic; Abdominal wall; Medical imagery; Acoustic antenna; Non linear effect; Acoustic image; Effective medium model; Apodization; Wall effect; Hydrophone
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2006.1665074

Techniques based on the nonlinearly generated second harmonic signal (tissue harmonic imaging) have rapidly supplanted linear (fundamental) imaging methods as the standard in two-dimensional echocardiography. Enhancements to the compactness of the nonlinearly generated second harmonic (2f) field component with respect to the fundamental (1f) field component are widely considered to be among the factors contributing to the observed image quality improvements. The objective of this study was to measure the impact of phase and amplitude aberrations resulting from propagation through an inhomogeneous tissue, on the beamwidths associated with: the fundamental (1f); the nonlinearly generated second harmonic (2f); and the linearly propagated, effective apodization signal at the same (2f) frequency. Modifications to the transmit characteristics of a phased-array imaging system were validated with hydrophone measurements. Results demonstrate that the characteristics of the diffraction pattern associated with the linear-propagation effective apodization transmit case were found to be in good agreement with the detailed spatial characteristics of the nonlinearly generated second harmonic field. The effects of the abdominal wall tissue aberrators are apparent for all three of the beam profiles studied. Consistent with the improved image quality associated with harmonic imaging, the aberrated nonlinearly generated second harmonic beam was shown to remain more compact than the corresponding aberrated fundamental beam patterns in the presence of the interposed aberrator.