Acoustic Property Reconstruction of a Neonate Yangtze Finless Porpoise's (Neophocaena asiaeorientalis) Head Based on CT Imaging

Abstract

The reconstruction of the acoustic properties of a neonate finless porpoise’s head was performed using X-ray computed tomography (CT). The head of the deceased neonate porpoise was also segmented across the body axis and cut into slices. The averaged sound velocity and density were measured, and the Hounsfield units (HU) of the corresponding slices were obtained from computed tomography scanning. A regression analysis was employed to show the linear relationships between the Hounsfield unit and both sound velocity and density of samples. Furthermore, the CT imaging data were used to compare the HU value, sound velocity, density and acoustic characteristic impedance of the main tissues in the porpoise’s head. The results showed that the linear relationships between HU and both sound velocity and density were qualitatively consistent with previous studies on Indo-pacific humpback dolphins and Cuvier’s beaked whales. However, there was no significant increase of the sound velocity and acoustic impedance from the inner core to the outer layer in this neonate finless porpoise’s melon.

Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam

“…Then the distribution of HU values of all the structures was derived from CT data. On the basis of the HU distribution, the distributions of sound velocity and density of all the structures in the animal's head can be reconstructed (see more details in Wei et al, 2015). The results were qualitatively consistent with the previous studies on Cuvier's beaked whale from Soldevilla et al (2005) and Indo-pacific humpback dolphins from Wei et al (2013).…”

“…Sound velocity of tissue is temperature dependent, and the sound velocity values from Wei et al (2015) were measured at 23 C, which is below the temperature of the melon in a living animal's head. The melon is vascularized, which has been hypothesized to be related to its thermoregulation by Houser et al (2004).…”

“…Unfortunately, no tissue properties measurements were performed on this harbor porpoise. However, Wei et al (2015) sliced a neonate Yangtze finless porpoise's head transversely across the body axis and measured the sound velocity and density of the soft tissues including the melon, blubber, muscle, mandibular fat, connective tissue. The HU values of the corresponding slices were obtained from high resolution computed tomography scanning data (the CT data were obtained on the next day after the animal died, so the specimen was very fresh).…”

“…The results were qualitatively consistent with the previous studies on Cuvier's beaked whale from Soldevilla et al (2005) and Indo-pacific humpback dolphins from Wei et al (2013). Since the mammalian tissue properties are conserved at the same temperature (Duck, 1990), The HU-to-sound velocity and HU-to-density relationships from Wei's measurement results (Wei et al, 2015) were used in this study. The distributions of sound velocity, density, and acoustic impedance values of the different structures in the harbor porpoise's head including soft tissues, bony structures, and air spaces were calculated based on the distribution of HU values derived from the CT data, shown as in Fig.…”

Finite element simulation of broadband biosonar signal propagation in the near- and far-field of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

“…No tissue property measurements were performed on the bottlenose dolphin's head. However, the studies regarding the relationships between animal tissue properties and Hounsfield Unit (HU) values have shown similar results from different species (Soldevilla et al, 2005;Wei et al, 2015). Therefore, we assumed that the relationships between tissue properties and HU values in the bottlenose dolphins are similar to those of the Yangtze finless porpoise (Neophocaena asiaeorientalis) obtained by tissue property measurements in Wei et al (2015).…”