Feature Of The Week: High-speed full-range spectral domain correlation mapping optical coherence tomography for in vivo microcirculation imaging applications
Microcirculation imaging is a key parameter for studying the pathophysiological processes of various disease conditions, in both clinical and fundamental research. Recently, the functional extension of the OCT technique to image depth-resolved microcirculation has become a very promising area of research. There is a growing interest in the field of development of various types of OCT-based angiographic techniques, which aims to visualize the lumens and architecture of blood vessels in many clinical and fundamental areas of research, including cardiology, dermatology, neurology, ophthalmology, small animal imaging studies, and so forth. OCT-based angiography techniques utilize the red blood cell scattering dynamics as contrast mechanism, which exhibits phase or amplitude fluctuations over time, while the static tissue scattering is relatively constant over time. There are mainly three categories of OCT-based angiography methods, which are essentially based on the utilization of the complex nature of the OCT signal to obtain the microcirculation map: phase-based techniques, magnitude-based techniques, and techniques that use the complex data incorporating both magnitude and phase information.
Correlation mapping OCT (cm-OCT) is another purely magnitude-based angiography technique developed by our group, which takes advantage of the time-varying speckle effect, which is normally dominant in the vicinity of vascular regions compared to static tissue region. It utilizes the correlation coefficient as a direct measurement of decorrelation between two adjacent B-frames to enhance the visibility of microcirculation.
In this study, we present an improved cm-OCT technique based on a custom-built high-speed SDOCT system and introduced a modified scanning protocol with full-range complex-conjugate-free imaging capability. The modified scanning protocol measures repeated B-scans at the same location to generate a high-sensitivity correlation map between successive B-frames and a constant modulation frequency was introduced into the spatial interferograms to provide complex-conjugate-free cm-OCT images. Thus, this method has the additional advantages of doubling the depth range, which enables access to the high-sensitivity imaging region close to the zero optical path delay (OPD). We implemented the full-range imaging by offsetting the sample beam from the pivot axis of the x-scanner. This causes a path length modulation during x-scanning, thus introducing a modulation frequency in the B-scan interferograms. Another advantage of this method is that any additional phase shifting elements normally needed to realize frequency modulation in a single B-scan are avoided. Furthermore, the modulation frequency is inherently given by the system itself. These aspects provide us a potential to achieve high-speed full-range complex cm-OCT imaging without restriction on any additional hardware component, and without limitation on the imaging speed, which is important for in vivo imaging applications. This scanning protocol can provide better background suppression and wide scanning with a relatively short acquisition time.
For more information see recent Article. Courtesy of Hrebesh Subhash and Martin Leahy from National University of Ireland, Galway.