Detecting smoke-induced airway injury with 3-D, swept-source OCT

Gary Boas, gary.boas@photonics.com

Smoke-inhalation injury is a major cause of morbidity and mortality among victims of fires; airway injury, edema, swelling, sloughing and necrosis with airway obstruction are the major causes of complications in the wake of such injury. However, the ability to detect these changes, especially in a quantitative way, is currently very limited.

Optical coherence tomography (OCT) could offer a means to detect these changes, “particularly early changes that may be indicative of more severe later sequelae, and assist with clinical decision-making,” said Dr. Matthew Brenner, a pulmonologist and researcher with the Beckman Laser Institute and the Irvine Medical Center, both at the University of California, Irvine.

Researchers have reported use of three-dimensional, swept-source optical coherence tomography for detection of smoke-induced airway injury. Shown is a 3-D rendering of a rabbit trachea (a), an initial longitudinal baseline image with motion artifacts resulting from the cardiac cycle (b) and a baseline image with the artifacts corrected using specially developed software (c). Panel (d) shows a two-hour post-exposure image also with motion artifacts corrected. Courtesy of the Beckman Laser Institute and the Irvine Medical Center at the University of California, Irvine.

Brenner and colleagues had shown previously that three-dimensional OCT would be necessary to achieve more complete imaging capabilities for smoke-inhalation injury, especially as this type of injury can be local/regional and inhomogeneous. Now, in the Nov./Dec. 2009 issue of the Journal of Biomedical Optics, they have demonstrated early detection of smoke-induced airway injury in animals by incorporating a swept-source laser system, which allows much more rapid image acquisition and, thus, practical 3-D OCT imaging.

The investigators obtained 3-D volumetric images of the airway by performing circumferential scanning with a microelectromechanical systems motor-based probe. A translational stage pulled back the probe, facilitating 3-D helical scanning. For image acquisition, they used a swept source made by Santec Corp. of Aichi, Japan, with a center wavelength of 1310 nm, output power of 5 mW and a scanning rate of 20 kHz.

The generated data sets were large, said Zhongping Chen, a researcher in the university’s Department of Biomedical Engineering and at the Beckman Laser Institute, and the other senior author on the paper. He noted that the three-dimensional reconstructions required a fair amount of postprocessing. Most importantly, he and his team had to develop software algorithms for realignment of image stacks to eliminate cardiogenic motion in the reconstructions.

The swept-source OCT system could prove an important clinical tool. “Generally, clinicians rely on bronchoscopic imaging to determine the extent of airway injury and swelling post-smoke exposure,” Brenner said. Bronchoscopic imaging is invasive, however, and “intermittent at best.” Moreover, it is not quantitative and does not visualize subsurface abnormalities well.

Still, researchers must overcome a number of hurdles before widespread implementation of the system is possible. First, the systems must be made more user-friendly, “essentially turnkey.” Also, both the image reconstruction software and the methods employed to eliminate motion artifacts will have to be automated. And, finally, clinical studies will have to be performed, examining the longer-term relationships between early and ongoing OCT findings and histopathological and clinical medical outcomes.