Anatomical OCT

Also see: What is Anatomical OCT?

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.

For the upper airway, OCT has allowed high-resolution structural imaging during sleep studies without the radiation exposure of CT or fluoroscopy, or the noise and logistical considerations of MRI.

A typical acquisition is shown below. The bright yellow outline is the air-tissue interface of the upper airway, showing the shape of the airway. Click on the image to see the probe being pulled back through the entire upper airway. A 3D reconstruction of a different airway is shown on the right.

Pullback of aOCT probe, along the upper airway Click to play movie [4.61 MB]

3D reconstruction of the upper airway Click to play movie

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.

aOCT images of airway during collapse in obstructive sleep apnoea Click to play movie

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 at each air pressure is colour-coded to show how the shape varies as air pressure changes.

Airway compliance. Red = 3 cm H2O, blue = 6 cm H2O, green = 12 cm H2O.

References

1. J. 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.
2. D. D. Sampson, J.J. Armstrong, M.S. Leigh, D.R. Hillman, P.R. Eastwood, Imaging human upper airway architecture dynamically using optical coherence tomography, 8th International Conference on Optics Within Life Sciences, Melbourne, Australia, February, November 28-December 1, 2004, pp. 143-144.
3. J. J. Armstrong, M. S. Leigh, I. D. Walton, A. V. Zvyagin, S. A. Alexandrov, S. Schwer, D. D. Sampson, D. R. Hillman, P. R. Eastwood, In vivo size and shape measurement of large hollow organs using endoscopic long-range optical coherence tomography, Opt. Express, vol. 11, no. 15, pp. 1817-1826, 2003.
4. M. S. Leigh, J. J. Armstrong, A. Paduch, J. H. Walsh, D. R. Hillman, P. R. Eastwood, D. D. Sampson, Anatomical optical coherence tomography: Endoscopic quantitative imaging of the upper airway, 18th International Optical Fiber Sensors Conference Technical Digest (ISBN: 1-55752-817-9, Optical Society of America, Washington, DC, 2006), Paper WA7.