Figueroa-Roldán, Héctor M.

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    Estimation of vessel wall compliance using acoustic reflectometry
    (2006) Figueroa-Roldán, Héctor M.; Juan-García, Eduardo J.; College of Engineering; Hunt, Shawn D.; Department of Electrical and Computer Engineering; Valentín, Ricky
    This thesis focuses on the estimation of rubber tube wall compliance using a pulse echo-acoustic reflectometry technique. Five rubber latex tubes of different thicknesses were studied using a transient acoustic pulse, instead of continuous sinusoidal waves. An acoustic Hanning pulse was designed with a wide bandwidth to study the resonance frequency of the tubes, and the tube wall compliance was estimated from reflection analysis. This method was applied using a reflectometer inside the tubes. Planar propagation was considered and given that the pulses travel into the system, the mechanical properties could be measured faraway, in contrast with other methods employed. An acoustic transmission line model was used to compute the natural frequency fr, the input characteristic acoustic impedance and to predict from them, the values of the transversal frequencies fres and f2. The natural frequency of the system occurs when the medium and wall tube vibrate at the same frequency, while the transversal frequencies occur when the characteristic impedance reaches minimum and maximum values, respectively. The wall compliance of rubber latex tubes was estimated via computer simulations, and acoustical and mechanical measurements. Two mathematical expressions were used to estimate the wall compliance C*w and C**w , which were compared to the mechanical measurement and model predictions of compliance. The wall compliance estimated acoustically, mechanically and simulated exhibited the same trend, with error averages for C*w of 77.7% and of 20.5% for C**w with respect to the values of compliance obtained from the transmission line model. Additionally, the error average between the values obtained mechanically and via simulation was 66.6%, with respect to the mechanical values. The results obtained from this research could serve as the groundwork for the development of a non-invasive device that can be used clinically to determine the pathological condition of compliant biological conduits such as veins, arteries and airways.