Acoustic reflectometry for airway measurement. Principles, limitations and previous work

Acoustic pulse reflectometry is a relatively recent technique which allows the non-invasive measurement of human airways. The technique consists of guiding an acoustic impulse through the subject's mouth and into the airway. Suitable analysis of the resulting reflection (the 'echo') allows a reconstruction of the area-distance function. The non-invasive nature of the technique offers significant advantages over the established methods of x-ray cephalometry and CT scanning, and makes it very attractive for the investigation of ENT problems and sleep apnoea, and in the anaesthetic management of patients. This paper describes the theory and limitations of acoustic reflectometry, discusses previous work, and suggests some modifications: it is currently being implemented clinically.