Indicators on lateral sagittal neck magnetic resonance image in the neutral position. MRI1: distance between the base of the tongue and the posterior pharyngeal wall; MRI2: distance between the epiglottis and the posterior pharyngeal wall; MRI3: distance between the uvula and the posterior pharyngeal wall; MRI4: distance between the vocal cords and the posterior pharyngeal wall; MRI5: length of the epiglottis.