Accuracy of acoustic rhinometry

OBJECTIVES: The objective of this study was to evaluate the ability of acoustic rhinometry (AR) (Rhin2100, Rhinometrics, Lynge, Denmark) to accurately determine the dimensions (cross-sectional areas and volumes) of the curved and complex slit-like geometry of the nasal airway. MATERIALS AND METHODS: A plastic model representing the replicate of a decongested nasal airway was produced by stereolithographic techniques from a 3-D MRI-scan. The exact dimensions of this model was determined from a high resolution CT-scan. Dimensions perpendicular to the curved course of the acoustic pathway were compared with dimensions inferred from parallel sections. The impact of sound loss to the paranasal sinuses and the ability to detect posterior volume changes was tested in the same model. RESULTS: The error in volume determination was < 14% for the MCA and < 8% for the volumes, whereas the error reached 52% for dimensions calculated from parallel sections in the coronal plane. The influence of the simulated maxillary sinuses depend primarily on the size of the ostia and may represent an important source of error for posterior measurements, in particular after decongestion. CONCLUSIONS: The accuracy of acoustically derived dimensions of the 3-D model depend on the orientation of the planes used to calculate the dimensions of the model. Volume estimates based on the smallest cross-sectional areas in points along the acoustic pathway correlate well with acoustically derived volumes, whereas single cross-sectional areas are more susceptible to error. Sound leakage to patent sinus ostia reduce the accuracy of posterior measurements.