Ultra-low-field magnetic resonance imaging in upper airways obstruction in sleep apnea syndrome

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Abstract
The hypothesis that the sites of upper airways obstruction (UAO) are varied in a patient with obstructive sleep apnea syndrome (OSAS) among different sleep stages is studied. Four patients with OSAS underwent ultra-low-field magnetic resonance imaging (MRI) with a field strength of 0.064 Tesla provided real-time images and generated less noise and necessitated less strict magnetic isolation compared with conventional high-field MRI. After the fixed end-apneic sleep stage was determined, the polysomnogram was switched off and ultra-low-field MRI was commenced. The effects of continuous positive airway pressure (CPAP) on the upper airway patency in the deepest sleep stage obtained for each patient was assessed. Upper airway obstruction was found at the level of the palatopharynx (PP) at sleep onset extended to the glossopharynx (GP) during rapid eye movement (REM) sleep in two cases and during NREM sleep in one case. This combined PP and GP obstruction was observed from sleep onset and remained unchanged in one case. The patent upper airways were observed during treatment with CPAP during REM sleep in two patients and during stage two of NREM sleep in the other two patients. It can be concluded that the sites of UAO vary in a patient with OSAS in different sleep stages. The results also suggest the use of the ultra-low-field MRI in order to visualize the dynamic and real-time behaviors of the upper airways during sleep in patients with OSAS.