**3. Imaging**

Xrays of the maxilla and mandible in the form of cephalometry5 may provide useful data of various parameters and dimensions controlling the upper airway. This can be particularly useful when the patient is being considered for invasive surgery such as maxillomandibular advancement or indeed when considering patients for MAS, though for the latter it is presently used for research purposes only. The limitation of this evaluation technique is that it provides a two dimensional image and that so during wakefulness. It also exposes the patient to considerable amount of radiation.

In contrast, computed tomography (CT) scanning and magnetic resonance imaging (MRI) provide more sophisticated imaging and allows objective cross sectional area and volumetric analysis. 6, 7 They are both more expensive than the cephalometry and the CT scans would also involve radiation. The MRI is quite noisy but is excellent at delineating soft tissue margins as well as fat deposition in the parapharyngeal space. For research reasons cine CT and dynamic MRI studies have been conducted to evaluate the upper airway but it is not considered to be practical or cost effective for routine use.
