This research extends OCT usage to endoscopic scanning of large-scale hollow organs. Specifically, we have developed an endoscopic OCT probe to map the 3-D shape and dynamics of the upper airway, including during sleep, for sleep apnoea research.
Section 1. What is anatomical OCT?
Anatomical OCT (aOCT) is a long-range scanning implementation of Optical Coherence Tomography (OCT) that maps internal anatomy as opposed to the conventional sub-surface morphology. It is used to provide endoscopic imaging of the anatomy of large, hollow organs, at a greater scale than is typically possible with OCT. It has been successfully applied to scanning of the upper airway, allowing the generation of 3D models showing the anatomical shape of the airway during sleep studies.
A limiting factor on the axial scan range of OCT systems is the optical delay line used in the low-coherence interferometer. By using a rapid-scanning frequency-domain optical delay line, we have achieved a scanning range of more than several centimeters.
Section 2. Clinical aOCT system
We have developed a clinical aOCT system in co-operation with researchers at the West Australian Sleep Disorders Research Institute at Sir Charles Gairdner Hospital.
The system consists of an endoscopic probe which is inserted into the patient through a catheter. The probe head utilizes a Gradient Index (GRIN) lens to focus the optical beam, and a small prism to redirect the beam perpendicular to the probe. A frequency-domain optical delay line is used to acquire each A-scan, and the probe head is rotated through 360 degrees within the catheter for a complete scan of the anatomy.
Section 3. Obstructive sleep apnoea
The clinical aOCT system developed within our lab is currently being used for research in obstructive sleep apnoea. In obstructive sleep apnoea, the patient suffers repeated interruptions to breathing due to a temporary collapse of part of the airway. It affects 2-4% of middle-aged adults and has been linked to hypertension and cardiovascular disease.
The aOCT probe is placed inside a catheter, which is then inserted through the nares (nostrils) to the level of the mid-oesophagus. The probe is rotated to obtain a profile of the upper airway, with a maximum imaging diameter of approximately 72mm. A controlled pullback of the probe through the airway allows the acquisition of a 3D image of the airway.
The image below demonstrates airway collapse during sleep apnoea. The blue graph plots air pressure, which drops to zero during airway collapse. The first aOCT image shows the shape of the airway during normal sleep breathing. In subsequent images, the airway narrows until collapse. At t = 19 seconds, the airway suddenly dilates as the patient takes a large breath. The final image shows the airway return to normal breathing.
Section 4. Airway compliance
aOCT has also been used to image airway compliance. The picture below shows a single section of airway imaged under different air pressures. The acquisition of each air pressure is colour-coded to show how the shape varies as air pressure changes.
Section 5. Anatomical OCT: quick links
1) Key applications
2) Key researchers
3) Key Publications
- J. Armstrong, M. S. Leigh, D. D. Sampson, J. H. Walsh, D. R. Hillman, and P. R. Eastwood, Quantitative upper airway imaging with anatomic optical coherence tomography, American Journal of Respiratory and Critical Care Medicine, vol. 173, pp. 226-233, 2006.
- S. Leigh, J. J. Armstrong, A. Paduch, J. H. Walsh, D. R. Hillman, P. R. Eastwood, D. D. Sampson, Anatomical optical coherence tomography for long-term portable quantitative endoscopy, IEEE Transactions on Biomedical Engineering, vol. 55, pp. 1438-1446, 2008
- A. McLaughlin, J. J. Armstrong, S. Becker, J. H. Walsh, A. Jain, D. R. Hillman, P. R. Eastwood and D. D. Sampson, Respiratory gating of anatomical optical coherence tomography images of the human airway, Optics Express, vol. 17, no. 8, pp. 6568-6577, 2009.
- B. Noble, A. R. West, R. A. McLaughlin, J. J. Armstrong, S. Becker, P. K. McFawn, J. P. Williamson, P. R. Eastwood, D. R. Hillman, D. D. Sampson and H. W. Mitchell, Airway narrowing assessed by anatomical optical coherence tomography in vitro: dynamic airway wall morphology and function, J. Applied Physiology, vol. 108, no. 2, pp. 401-411, 2010.