Creation of a Statistical Shape Model (SSM) of the head and airway to improve CPAP delivery in OSA using prospectively collected CT head scans

The study will consist of 4 stages: * Recruitment * Screening/Enrolment stage * CT Scan/Imaging * Follow up Stage Recruitment Up to 300 Adult OSA patients (AHI =15 on a sleep study within the last 6 years) and 20 normal controls (AHI less than 5 or, if no sleep study is available, an Epworth Sleepiness Score less than 10) will be recruited from the large network of Sleep Physicians and Otolaryngologists within the Western Sydney Local Health District. Screening/Enrolnment Stage Subject Informed Consent Prior to enrolment in this study, all subjects must review and complete an EC-approved PICF. All potential subjects must complete the consent process prior to undergoing procedures performed specifically for this study that are outside the standard of care for the institution. Failure to obtain a signed PICF renders the subject ineligible for the study. Site will comply with ICH guidelines for obtaining informed consent. Demographics Demographic information (age, gender, height, weight, ethnicity) will be obtained during Screening as specified in the Schedule of Assessments for Subjects enrolled Medical and Surgical history A general medical history will be collected. In addition, the medical history will document conditions focusing specifically on the following: Ear, Nose, and Throat, CPAP History, Sleep Study results, Epworth Sleepiness score, contraindications to Otrivin (Xylometazoline) nasal decongestant. If Otrivin is contraindicated, the subject will fail screening. CT Scan A single CT scan of the head and neck will be performed at high resolution (slice thickness 0.6mm) with low dose radiation at a single site (Castlereagh Imaging, Westmead) using a calibrated scanning device (Siemens Somatom Definition Flash) which has been certified by Gammasonics as compliant with the Australian National Dose Level. A nasal decongestant spray (Otrivin/ Xylometazoline Hydrochloride 1 mg/mL 1 spray bilaterally in each nostril) will be administered 15 mins prior to scanning. A nasal decongestant spray (Otrivin/ Xylometazoline Hydrochloride 1 mg/mL 1 spray bilaterally in each nostril) will be administered 15 mins prior to scanning. The CT scan will take a few minutes (less than 5) to perform. Follow Up Follow up will occur around 1-2 weeks after the scan and will include a discussion of CT scan report with a member of the study team. If any incidental abnormality is detected, a study team doctor will perform the discussion and help arrange any required follow-up. No interventions will be performed.