*8.4.2. Computed tomography (CT)*

The high-resolution and three-dimensional evaluation of the skeletal system and soft tissues in maxillofacial complex can be performed by computed tomography. CT imaging is done in supine position and can give us the opportunity of recording the changes in upper airway crosssectional area in different phases of respiration and predicting the collapse area in OSAS patients. The disadvantages of this technique are as follows: being expensive, high radiation level, and the low-resolution images of fat tissues around upper airway according to MR imaging [14].

#### *8.4.3. Magnetic resonance imaging (MRI)*

Magnetic resonance imaging allows 3D imaging and accurate measurement of the upper airway, soft tissues, and skeletal structures. MRI is performed in supine position, it allows high-resolution visualization of soft tissues and fat deposits around pharyngeal airway, and the volume and area of the airway can be measured accurately. With ultrafast mode dynamic observation can be done. But it is expensive and cannot be used in patients who have claustrophobia, ferromagnetic clips, or pacemaker [15].
