ACOUSTIC RHINOMETRY (AR): AN ALTERNATIVE METHOD TO IMAGE NASAL AIRWAY GEOMETRY. INTRODUCTION AND BACKGROUND: In human studies the acoustic reflection technique was first applied to describe the area-distance relationship of the lower airways, but later the acoustic reflection technique appeared to be of more use in the description of nasal cavity geometry. Applied to human subjects AR has been applied to monitor the effect of corrective surgery and mucosal effects of pharmacological interventions. In recent years, however, AR has found use also in pharmacological studies in animals ranging in size from dogs to guinea pigs. It is possible to measure relative changes in nasal congestion even in small animals, but absolute volumes seem to be underestimated. There is a need for further development to obtain better results of AR in small laboratory animals. METHOD: A sound pulse, generated by a spark, propagates through a sound tube and enters the nasal cavity. The reflected waves travel back through the tube and are recorded by a [OFP1] microphone. Measurements are computed from changes in the local impedance by comparing the incident and reflected acoustic pressure waves by inverse fast Fourier transform. Based on the Ware and Aki algorithm measurements are displayed as an area-distance curve where cross-sectional area of the nasal cavity is a function of distance travelled by the sound wave. DEMONSTRATION[OFP2] : Current problems using AR are demonstrated based on results from a few studies. - Acoustic measurements obtained from guinea pig post mortem. - Corresponding area-distance curve compared to actual CT imaging of the nasal cavity and a fluid-displacement method. DISCUSSION: The method has been utilized on increasingly challenging nasal cavity geometries in relation to both complexity and small size. This results in underestimation of cross-sectional areas and methodological difficulties related to data acquisition.A major challenge is to define the mathematical and physical limitations of AR in order to enhance the method to enable studies in small laboratory animals. Future prospects therefore could include development of new algorithms for computing data, more sensitive microphones measuring higher frequencies and optimal relationship between sound tube dimensions and the cavity measured. Achieving that may improve measurements, making pharmacological studies in laboratory animals more reliable. To accomplish this we hope to receive new input from adjacent fields of research. [OFP1] Det er ikke nogen piezoelektrisk mikrofon. Det er en ganske billig kondensator mikrofon. [OFP2] Jeg tror du kan nøjes med små figurer1) Indfaldende og reflekteret kurve fra marsvin2) Areal-afstandskurve beregnet fra ovennævnte med overlagt perflourocarbon-displacement kurve.
Acoustic Rhinometry; Airway Geometry
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28th International Symposium on Acoustical Imaging, 2005