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Authors
Publisher
Aalborg Universitet
Publication Date
Keywords
  • Bowel Sounds
  • Tdoa
  • 3-D Detection
  • Abdominal Speed Of Sound
  • Least Square Principle
  • Sound Localization

Abstract

3-D localization of bowel sounds using Time Delay of Arrival (TDoA) is an unexplored working field. A major difficulty related to using this technique for localizations in the abdominal area, is the variation in the speed of sound in different media. Based on the literature, it is assumed that intestinal gasses affects the speed of the abdominal sound propagation, and thereby the precision of the TDoA. In this study, a system for estimating a localization of a sound source using the TDoA, cross correlation and Least Squares Principle was set up. In order to determine eventual bias and reliability issues caused by the structure of the abdomen, two experiments were made. The first experiment was in vitro, where sound waves were propagated through free air. In the second experiment, in vivo, a sound created by a probe placed in the duodenum was propagated through the abdomen. The experiments were repeated six times. The sounds were recorded by eight stethoscopes positioned at known locations, and were evaluated based on the outcome of the single cross correlations. The sample standard deviations of the delays were relatively high in the measurements of the in vitro experiment. This indicates that the measurements of time delay suffers from errors associated to the developed system. These errors might be related to the placement or the properties of the stethoscopes. The sample standard deviations were distinctly higher in vivo indicating that the main reliability issues were related to the above mentioned influence of abdominal gasses. Therefore a practical useful model that describes abdominal velocity changes as well as more precise measurement equipment than ordinary stethoscopes were required in order to obtain precise 3-D location of abdominal sounds by using TDoA.

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