A systematic review of the literature concerning upper airway imaging and analysis using cone-beam computed tomography (CBCT) was performed. A PubMed search (National Library of Medicine, NCBI; revised 9th January 2011) yielded 382 papers published between 1968 and 2010. The 382 full papers were screened in detail. 46 articles were considered clinically or technically relevant and were included in this systematic review. These were classified as articles on accuracy and reliability of CBCT imaging of the upper airway ( n = 4), accuracy and reliability of DICOM viewers ( n = 2), synopsis ( n = 10), technical ( n = 7) and clinical applications ( n = 27). When one paper was considered related to two or more categories, it was assigned to each relevant group. Results indicate that three-dimensional (3D) analysis of the upper airway using CBCT can be achieved in an accurate and reliable manner. Important obstacles still need to be addressed, including the impact of respiration phase, influence of tongue position and mandible morphology, longitudinal and cross-sectional 3D CBCT upper airway evaluation, and 3D CBCT definition of the anatomical boundaries of the upper airway.
Since its development in the 1990s, cone-beam computed tomography (CBCT) has become a well-accepted tool for oral and maxillofacial (OMF) diagnosis and treatment planning, mainly due to its advantages in lower effective radiation dose, lower costs, easy access and shorter acquisition times in comparison to conventional multidetector CT (MDCT) (also called multislice CT, MSCT) .
Interest in upper airway shape and dimensions has increased steadily during the past decades mainly due to the relationship between upper airway configuration and obstructive sleep apnea (OSA) as well as craniofacial morphology. According to the medical literature, airway evaluation can be performed with magnetic resonance imaging (MRI) , cine-MRI , MDCT , endoscopy and optical coherence tomography . Although CBCT is inferior to MDCT in discriminating between different soft-tissue structures, it defines the boundaries between soft tissues and empty spaces with high spatial resolution . Several studies have tested its accuracy and reliability and have confirmed its potential for the evaluation of the upper airway . Post-processing of DICOM (Digital Imaging and Communications in Medicine) images by third-party software allows visualization and quantification of the airway in an unprecedented way. As a result, better understanding of the upper airway anatomy and physiology is to be expected .
The number of publications related to upper airway analysis with CBCT has increased during the last 5 years ( Fig. 1 ). Although some articles provide a synopsis of CBCT imaging of the OMF region and refer to the possibility of upper airway evaluation, a systematic review of CBCT imaging and analysis of the upper airway has not been published.
The purpose of this article was to conduct a systematic review of the literature on CBCT imaging and analysis of the upper airway in order to: (1) determine current and potential clinical indications of upper airway analysis with CBCT; (2) report technical parameters and verify the accuracy; and (3) reliability of CBCT for upper airway analysis according to the available studies.
Material and methods
A systematic review of the literature concerning upper airway imaging and analysis with CBCT was performed. A PubMed database (National Library of Medicine, NCBI) search was performed and updated on 9th January 2011. 12 primary keywords related to CBCT terminology were used in combination with 24 secondary keywords in order to restrict the search to CBCT evaluation of the upper respiratory tract relevant to the OMF region ( Table 1 ). All possible combinations between one primary keyword and each secondary keyword were explored. The upper respiratory tract was considered to comprise the respiratory structures above the trachea from the nostrils to the larynx.
|Primary keywords||Secondary keywords|
|1. Cone-beam||1. Air space|
|2. Conebeam||2. Airspace|
|3. CBCT||3. Airway|
|4. CB-CT||4. Upper airway|
|5. Digital volume tomography||5. Airflow|
|6. DVT||6. Pharynx|
|7. Compact computed tomography||7. Pharyngeal|
|8. Compact CT||8. Oropharynx|
|9. Volumetric computed tomography||9. Oropharyngeal|
|10. Volumetric CT||10. Nasopharynx|
|11. Ortho cubic||11. Nasopharyngeal|
|12. Flat panel||12. Hypopharynx|
|20. Obstructive sleep apnea syndrome|
|21. Obstructive sleep apnea|
|22. Sleep apnea|