Computed Tomography

CT is a noninvasive technique that permits a thorough evaluation of the entire upper airway. CT techniques employed to study the upper airway include standard axial CT images with the option to three-dimensionally reconstruct the upper airway

FIGURE 4 Axial magnetic resonance imaging in the retropalatal region of a normal subject (left) and a patient with sleep apnea (right). The upper airway is smaller in the lateral dimension in the patient with sleep apnea. The apneic patient has more subcutaneous fat than the normal subject. Source: From Ref. 23.

FIGURE 4 Axial magnetic resonance imaging in the retropalatal region of a normal subject (left) and a patient with sleep apnea (right). The upper airway is smaller in the lateral dimension in the patient with sleep apnea. The apneic patient has more subcutaneous fat than the normal subject. Source: From Ref. 23.

Tongue Mandible Soft Palate Airway

Tongue Mandible Soft Palate Airway

Tongue Mandible Sott Palate Airway

FIGURE 5 (See color Insert.) Volumetric reconstruction of axial magnetic resonance images in a normal subject (top panel) and a patient with sleep apnea (bottom panel). The mandible is depicted in gray, the tongue in orange/rust, the soft palate in purple, the lateral parapharyngeal fat pads in yellow, and the lateral/posterior pharyngeal walls in green. Both subjects had an elevated body mass index (32.5 kg/m2). The airway is larger in the normal subject than in the patient with sleep apnea. The tongue, soft palate, and lateral pharyngeal walls are all larger in the patient with sleep apnea than in the normal subject. Source: From Ref. 29.

FIGURE 5 (See color Insert.) Volumetric reconstruction of axial magnetic resonance images in a normal subject (top panel) and a patient with sleep apnea (bottom panel). The mandible is depicted in gray, the tongue in orange/rust, the soft palate in purple, the lateral parapharyngeal fat pads in yellow, and the lateral/posterior pharyngeal walls in green. Both subjects had an elevated body mass index (32.5 kg/m2). The airway is larger in the normal subject than in the patient with sleep apnea. The tongue, soft palate, and lateral pharyngeal walls are all larger in the patient with sleep apnea than in the normal subject. Source: From Ref. 29.

structures (30,31), electron beam CT that permits dynamic evaluation, and helical CT scanners (32,33) that have the ability to provide volumetric images. CT scanning, however, has limited soft-tissue contrast resolution compared with MRI scanning. This is particularly relevant to evaluating upper airway adipose tissue. Other l imitations of CT scanning include expense and the radiation exposure patients receive each time they are studied. Nonetheless, upper airway imaging studies with CT scanning has enhanced our understanding of upper airway anatomy and its relationship to OSA (30-49).

Most of the studies using CT have evaluated airway dimension during states of wakefulness and sleep and have shown narrowing predominantly in the retro-palatal region in patients with OSA (31,34-49). In addition, the degree of narrowing has been correlated directly with OSA severity (40). Volumetric CT studies have demonstrated smaller airway caliber and larger tongue volume in obese patients with OSA (31,50). Three-dimensional CT has shown that the most important parameter associated with sleep-disordered breathing appears to be narrowing at the retro-palatal area (30) and that lateral airway caliber compromise correlates with the apnea-hypopnea index (AHI). CT studies have also been employed to try to identify favorable surgical candidates for uvulopalatopharyngoplasty (UPPP) and to examine dynamic changes of the upper airway and surrounding soft tissue structures during respiration (15,20,51-53). These dynamic CT imaging studies have shown that the upper airway is narrowest at end-expiration and early-inspiration in both normal and apneic subjects (15,20,52,53).

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