Accuracy of acoustic rhinometry

Objectives: The objective of this study was to evaluate the ability of acou stic 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 deco ngested 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 ac oustic pathway were compared with dimensions inferred from parallel section s. The impact of sound loss to the paranasal sinuses and the ability to det ect posterior volume changes was tested in the same model Results: The error in volume determination was < 14% for the MCA and <8% fo r the volumes, whereas the error reached 52% for dimensions calculated from parallel sections in the coronal plane. The influence of the simulated max illary sinuses depend primarily on the size of the ostia and may represent an important source of error for posterior measurements, in particular afte r decongestion. Conclusions: The accuracy of acoustically derived dimensions of the 3-D mod el 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 deri ved volumes, whereas single cross-sectional areas are more susceptible to e rror. Sound leakage to patent sinus ostia reduce the accuracy of posterior measurements.