Novel retrospective, respiratory-gating method enables 3D, high resolution, dynamic imaging of the upper airway during tidal breathing.

PURPOSE: A retrospective, respiratory-gated technique for measuring dynamic changes in the upper airway over the respiratory cycle was developed, with the ultimate goal of constructing anatomically and functionally accurate upper airway models in obstructive sleep apnea patients.
METHODS: Three-dimensional cine, retrospective respiratory-gated, gradient echo imaging was performed in six adolescents being evaluated for polycystic ovary syndrome, a disorder with a high obstructive sleep apnea prevalence. A novel retrospective gating scheme, synchronized to flow from a nasal cannula, limited image acquisition to predefined physiological ranges. Images were evaluated with respect to contrast, airway signal leakage, and demonstration of dynamic airway area changes.
RESULTS: Two patients were diagnosed with obstructive sleep apnea. Motion artifacts were absent in all image sets. Scan efficiency ranged from 48 to 88%. Soft tissue-to-airway contrast-to-noise ratio varied from 6.1 to 9.6. Airway signal leakage varied between 10 and 17% of soft tissue signal. Automated segmentation allowed calculation of airway area changes over the respiratory cycle. In one severe apnea patient, the technique allowed demonstration of asynchronous airway expansion and contraction above and below a severe constriction.
CONCLUSIONS: Retrospective, respiratory gated imaging of the upper airway has been demonstrated, utilizing a gating algorithm to ensure acquisition over specified ranges of respiratory rate and tidal volume.