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In a recent study a new analytical solution was developed and validated experimentally for the problem of surface wave generation on a linear viscoelastic half-space by a rigid circular disk located on the surface and oscillating normal to it. The results of that study suggested that, for the low audible frequency range, some previously reported values of shear viscosity for soft biological tissues may be inaccurate. Those values were determined by matching radiation impedance measurements with theoretical calculations reported previously. In the current study, the sensitivity to shear viscoelastic material constants of theoretical solutions for radiation impedance and surface wave motion are compared. Theoretical solutions are also compared to experimental measurements and numerical results from finite-element analysis. It is found that, while prior theoretical solutions for radiation impedance are accurate, use of such measurements to estimate shear viscoelastic constants is not as precise as the use of surface wave measurements.

An acoustic boundary element (BE) model is used to simulate sound propagation in the lung parenchyma. It is computationally validated and then compared with experimental studies on lung phantom models. Parametric studies quantify the effect of different model parameters on the resulting acoustic field within the lung phantoms. The BE model is then coupled with a source localization algorithm to predict the position of an acoustic source within the phantom. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm does not perform as well if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. The BE model and source localization procedure are then applied to actual lung geometry taken from the National Library of Medicine’s Visible Human Project. These numerical studies are in agreement with the studies on simpler geometry in that use of a BE model in place of the free field assumption alters the predicted acoustic field and source localization results. This work is relevant to the development of advanced auscultatory techniques that utilize multiple noninvasive sensors to construct acoustic images of sound generation and transmission to identify pathologies.

A theoretical and experimental study was undertaken to examine the feasibility of using audible-frequency vibro-acoustic waves for diagnosis of pneumothorax, a collapsed lung. The hypothesis was that the acoustic response of the chest to external excitation would change with this condition. In experimental canine studies, external acoustic energy was introduced into the trachea via an endotracheal tube. For the control (nonpneumothorax) state, it is hypothesized that sound waves primarily travel through the airways, couple to the lung parenchyma, and then are transmitted directly to the chest wall. In contradistinction, when a pneumothorax is present the intervening air presents an added barrier to efficient acoustic energy transfer. Theoretical models of sound transmission through the pulmonary system and chest region to the chest wall surface are developed to more clearly understand the mechanisms of intensity loss when a pneumothorax is present, relative to a baseline case. These models predict significant decreases in acoustic transmission strength when a pneumothorax is present, in qualitative agreement with experimental measurements. Development of the models, their extension via finite element analysis, and comparisons with experimental canine studies are reviewed.

An analytical solution is developed for the problem of surface wave generation on a linear viscoelastic half-space by a finite rigid circular disk located on the surface and oscillating normal to it. The solution is an incremental advancement of theoretical work reported in articles focused on seismology. Since the application of interest here is medical diagnostics, the solution is verified experimentally using a viscoelastic phantom with material properties comparable to biological soft tissue. Findings suggest that prior estimates in the literature of the shear viscosity in human soft tissue may not be accurate in the low audible frequency range. Measurement of wave motion on the skin surface caused by internal biological functions or external stimuli has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in tissue shear elasticity or variations in density due to gaseous inclusions.

Acoustic wave propagation in the pulmonary system and torso is simulated by coupling a numerical acoustic boundary element model that predicts sound propagation throughout the solid tissues with a proven comprehensive analytical model for sound wave propagation in the airways of the bronchial tree that is valid up to at least 2 kHz. This approach enables modeling various pathologies that result in structural changes in the lung and/or changes in breath sound source and strength. The model may be also used to predict the resulting acoustic changes measured by acoustic sensors, e.g., stethoscopes, accelerometers, or other skin‐contact sensors. Experimental studies in a novel lung phantom model are used to partially validate the computational model. This study focuses on low audible frequencies, i.e., less than 2 kHz. This range encompasses naturally generated respiratory sounds that have been shown to have diagnostic value, as well as externally‐introduced vibro‐acoustic stimuli used for diagnosis. [Work supported by NIH EB 003286‐01.]

Diagnostic techniques are provided to enable the detection of a respiratory condition with a patient's body. The diagnostic techniques compare the acoustic generation and transmission characteristics of the patient's chest and lungs to reference acoustic characteristics and/or predetermined threshold values to determine if an abnormal respiratory condition is present within the patient. The diagnostic techniques process sound waves or vibrations that have interacted with a respiratory condition within a patient and which impinge on the chest wall of the patient. The sound waves or vibrations may be initiated by a speaker (20) that emits sounds waves into the mouth and trachea of the patient (12) or may be indigenous sounds. Alternatively, the sounds waves or vibrations may be initiated using percussive inputs to the chest wall of the patient (12). In processing (38) the sound waves, the diagnostic techniques calculate energy ratios using energy values within high and low frequency bands, signal time delays, and/or dominant frequencies and compare the calculated values to predetermined reference thresholds to generate outputs indicative of the respiratory condition within the patient.

Small bowel obstruction (SBO) is a common surgical emergency which may be mimicked by ileus or other nonsurgical conditions. The aims of this work is to delineate gastrointestinal sound (GIS) correlates in a rat model. Seven rats were studied in paired SBO and control states. Computerized analysis of GIS was performed under continuous IV sedation. After adaptive filtering, every GIS event was isolated and analyzed for duration and dominant frequency. It was found that long duration sounds (greater than 100 ms) occurred in each of the obstructed, but in none of the nonobstructed cases (p=0.02). The overall mean event duration and dominant frequency in SBO compared to control states was both significantly longer and lower (22.42.6 vs 7.0±2.6 ms, p=0.001 for duration; and 296±34 vs 427±33, p=0.001 for frequency). Besides these mean differences, there was also a clear evolution with time in GIS characteristics, with lengthening of the duration (+0.56 ms/min, p=0.001) and lowering of the dominant frequency (−3.3 Hz/min, p=0.01). It is concluded that GIS analysis may prove useful in the noninvasive, rapid, and accurate diagnosis of SBO.