Feature Of The Week 9/19/10: Researchers from University of Central Florida and University of Rochester demonstrate Doppler Imaging with Dual-Detection Full-Range Frequency Domain Optical Coherence Tomography
Feature Of The Week 9/19/10: Recent development in Doppler optical coherence tomography (DOCT) is mostly based on phase sensitive detection so-called phase-resolved DOCT. It is commonly known that the performances of phase-resolved Doppler OCT, such as the stability and accuracy of the measured Doppler phase shift, highly rely on the signal-to-noise ratio (SNR). Therefore, the ability to employ a maximum SNR out of a given phase-resolved DOCT system is desirable. Even though, the high speed imaging capability of FD-OCT is attractive for real time in vivo monitoring of flow activity in biological sample as well as for 3D flow segmentation, the main challenges in conventional FD-OCT are the existence of the mirror image and the limited spectral resolution of the detected spectral interference signal. The demand of high axial-resolution at high acquisition speed requires sacrificing spectral resolution that eventually leads to a reduction in the imaging depth range. Therefore, the removal of the mirror image in FD-OCT is desirable to double the imaging depth range as well as efficiently utilize the maximum sensitivity out of a FD-OCT system. Nevertheless, most of full-range techniques for FD-OCT reported to date utilize the phase relation between consecutive axial lines to reconstruct a complex interference signal and hence may exhibit degradation in either mirror image suppression performance or detectable velocity dynamic range or both when monitoring a moving sample such as flow activity.
Researchers Panomsak Meemon, Kye-Sung Lee, and Jannick Rollard from The College of Optics and Photonics at the University of Central Florida and The Institute of Optics at the University of Rochester, addressed these issues in a novel method called dual-detection full-range FD-OCT (DD-FD-OCT). DD-FD-OCT simultaneously detects two spectral interferences that have pi/2 phase relation representing real and imaginary components of the complex spectral interference signal. One main advantage of the DD-FD-OCT over other full-range techniques is that the full-range signal is achieved without manipulation of the phase relation between consecutive axial lines. Hence the full-range DD-FD-OCT is fully applicable to phase-resolved DOCT without degradation in both detectable velocity dynamic range and mirror image rejection performance. Moreover, by combining the full-range capability to phase-resolved Doppler imaging, the region of interest can be placed close to the zero-delay position and the highest SNR around this region can be utilized to improve flow visibility and sensitivity in biological samples.
As shown here, the researchers implemented the DD-FD-OCT in a swept-source-based FD-OCT built on a combination of fiber and free-space using a Mach-Zehnder interferometer (MZI) setup. The velocity sensitivity of Doppler DD-FD-OCT was quantified through the measurement of Doppler phase shift error when imaging a stationary mirror. The degradation of the Doppler phase stability as a function of axial position was also verified, motivating the need of mirror image removal in FD-OCT. In addition, the relation between the measured Doppler phase shift and the set flow velocity of a flow phantom was measured. The results demonstrated that the Doppler imaging with full-range DD-FD-OCT exhibits no reduction in detectable velocity range as compared with that measured by conventional methods. As one illustration of this technique Doppler imaging of an in vivo African frog tadpole using DD-FD-OCT is shown.
For more information see recent Article. Courtesy of Panomsak Meemon.