Volume 116, Issue 2, August 2004
Index of content:
- BIOACOUSTICS 
Theoretical study in applications of doublet mechanics to detect tissue pathological changes in elastic properties using high frequency ultrasound116(2004); http://dx.doi.org/10.1121/1.1768252View Description Hide Description
The mathematical framework of a new elastic theory—doublet mechanics (DM)—was reviewed. The fundamental difference between DM and classical continuum mechanics (CCM) is that the former has taken the discrete nature of tissue on the cellular level into account and the latter assumes tissue is uniform and continuous. Theoretical calculations based on DM were performed for reflection coefficients of a substrate–tissue layer–substrate assembly. Results of computer simulations have shown that ultrasoundreflection coefficients in the range of 15–30 MHz are sensitive to changes in cell size and elastic moduli of tissue according to DM but not to CCM. Potential experimental applications of this technique to tissue characterization are discussed.
Amplification and spectral shifts of vocalizations inside burrows of the frog Eupsophus calcaratus (Leptodactylidae)116(2004); http://dx.doi.org/10.1121/1.1768257View Description Hide Description
A variety of animals that communicate by sound emit signals from sites favoring their propagation, thereby increasing the range over which these sounds convey information. A different significance of calling sites has been reported for burrowing frogs Eupsophus emiliopugini from southern Chile: the cavities from which these frogs vocalize amplify conspecific vocalizations generated externally, thus providing a means to enhance the reception of neighbor’s vocalizations in chorusing aggregations. In the current study the amplification of vocalizations of a related species, E. calcaratus, is investigated, to explore the extent of sound enhancement reported previously. Advertisement calls broadcast through a loudspeaker placed in the vicinity of a burrow, monitored with small microphones, are amplified by up to 18 dB inside cavities relative to outside. The fundamental resonant frequency of burrows, measured with broadcast noise and pure tones, ranges from 842 to 1836 Hz and is significantly correlated with the burrow’s length. Burrows change the spectral envelope of incoming calls by increasing the amplitude of lower relative to higher harmonics. The call amplification effect inside burrows of E. calcaratus parallels the effect reported previously for E. emiliopugini, and indicates that the acoustic properties of calling sites may affect signal reception by burrowing animals.
116(2004); http://dx.doi.org/10.1121/1.1763956View Description Hide Description
Many vocalizations produced by Weddell seals (Leptonychotes weddellii) are made up of repeated individual distinct sounds (elements). Patterning of multiple element calls was examined during the breeding season at Casey and Davis, Antarctica. Element and interval durations were measured from 405 calls all elements in length. The duration of the calls did not seem to vary with an increasing number of elements because element and interval durations decreased as the number of elements within a call increased. Underwater vocalizations showed seven distinct timing patterns of increasing, decreasing, or constant element and interval durations throughout the calls. One call type occurred with six rhythm patterns, although the majority exhibited only two rhythms. Some call types also displayed steady frequency changes as they progressed. Weddell seal multiple element calls are rhythmically repeated and thus the durations of the elements and intervals within a call occur in a regular manner. Rhythmical repetition used during vocal communication likely enhances the probability of a call being detected and has important implications for the extent to which the seals can successfully transmit information over long distances and during times of high level background noise.
The effect of loading on disturbance sounds of the Atlantic croaker Micropogonius undulatus: Air versus water116(2004); http://dx.doi.org/10.1121/1.1736271View Description Hide Description
Physiological work on fish sound production may require exposure of the swimbladder to air, which will change its loading (radiation mass and resistance) and could affect parameters of emitted sounds. This issue was examined in Atlantic croaker Micropogonius chromis by recording sounds from the same individuals in air and water. Although sonograms appear relatively similar in both cases, pulse duration is longer because of decreased damping, and sharpness of tuning (Q factor) is higher in water. However, pulse repetition rate and dominant frequency are unaffected. With appropriate caution it is suggested that sounds recorded in air can provide a useful tool in understanding the function of various swimbladder adaptations and provide reasonable approximation of natural sounds. Further, they provide an avenue for experimentally manipulating the sonic system, which can reveal details of its function not available from intact fish underwater.
Adapting the Lagrangian speckle model estimator for endovascular elastography: Theory and validation with simulated radio-frequency data116(2004); http://dx.doi.org/10.1121/1.1771615View Description Hide Description
Intravascular ultrasound(IVUS) is known to be the reference tool for preoperative vessel lesion assessments and for endovascular therapy planning. Nevertheless, IVUS echograms only provide subjective information about vessel wall lesions. Since changes in the vascular tissue stiffness are characteristic of vessel pathologies, catheter-based endovascular ultrasoundelastography (EVE) has been proposed in the literature as a method for outlining the elastic properties of vessel walls. In this paper, the LagrangianSpeckle Model Estimator (LSME) is formulated for investigations in EVE, i.e., using a polar coordinate system. The method was implemented through an adapted version of the Levenberg-Marquardt minimization algorithm, using the optical flowequations to compute the Jacobbian matrix. The theoretical framework was validated with simulated ultrasound rf data of mechanically complex vessel wall pathologies. The results, corroborated with Ansys finite element software, demonstrated the potential of EVE to provide useful information about the heterogeneous nature of atherosclerotic plaques.