OCT Phase Research Articles

A method of fast locating discrete interface based on phase information of complex master-slave optical coherence tomography

Spectral-domain optical coherence tomography (SD-OCT) system has the advantages of non-invasive, non-contact, fast imaging and low cost. It has important applications in the measurement of discrete interface of optical lens. However, the interference spectrum collected by spectral domain OCT system inevitably encounters some problems such as the unequal interval spectrum sampling and chromatic dispersion between two interference arms. In order to ensure that the axial resolution and sensitivity of the system are not reduced, subsequent data processing steps such as spectrum resampling and dispersion compensation need adding, which greatly reduces the real-time performance of measurement. In addition, in the actual measurement process, the required imaging area is often only a small part of the whole imaging area, the calculation of the whole imaging area brings a certain waste of computing power and resources. Moreover, in the positioning of discrete interface, the existence of sub-pixel deviation under limited axial resolution limits the measurement accuracy of interface. To solve the above problems, in this work proposed is a method of fast locating discrete interfaces based on complex master slave (CMS) OCT phase information. By combining the phase information of spectral domain and depth domain, the reconstruction template of CMS-OCT is solved accurately, and the phase information of CMS-OCT is used to achieve high-precision optical path difference detection and discrete interface location. Finally, experiments with precise optical gauge and discrete interface of optical lens verify that the proposed method can maintain high resolution and stability while fast locating is implemented.

Optical coherence elastography of bilayer soft tissue based on harmonic surface wave spectroscopy

Diseases often initiate from a certain layer of the biological tissue, thus simultaneous measurement of the elastic modulus of each layer is important for early diagnosis and treatment of various diseases. A surface wave spectroscopy (SWS) optical coherence elastography (OCE) technique based on harmonic wave excitation was proposed. An actuator consisting of a piezoelectric stack with a pin was designed to generate harmonic surface waves. A B-mode OCT data acquisition and phase analysis method was proposed to image the wave forms, and calculate the surface wave velocity. By exciting the sample with different frequencies, the surface wave dispersion curves were obtained. A total variation (TV) regularization iterative algorithm was proposed to obtain the elastic modulus distribution along the depth. Effectiveness of the proposed method was evaluated by both finite element simulation and experimental measurement of a bi-layer phantom. The mechanically driven harmonic wave actuation based OCE method is simple and cost-effective in experimental setup. Based on B-mode OCT scans, data analysis can be very fast, which is possible to realize real-time elastography imaging. This study provides an effective method for biomechanical properties study of layered tissue.

Measurement and visualization of stimulus-evoked tissue dynamics in mouse barrel cortex using phase-sensitive optical coherence tomography.

We describe a method to measure tissue dynamics in mouse barrel cortex during functional activation via phase-sensitive optical coherence tomography (PhS-OCT). The method measures the phase changes in OCT signals, which are induced by the tissue volume change, upon which to localize the activated tissue region. Phase unwrapping, compensation and normalization are applied to increase the dynamic range of the OCT phase detection. To guide the OCT scanning, intrinsic optical signal imaging (IOSI) system equipped with a green light laser source (532 nm) is integrated with the PhS-OCT system to provide a full field time-lapsed images of the reflectance that is used to identify the transversal 2D localized tissue response in the mouse brain. The OCT results show a localized decrease in the OCT phase signal in the activated region of the mouse brain tissue. The decrease in the phase signal may be originated from the brain tissue compression caused by the vasodilatation in the activated region. The activated region revealed in the cross-sectional OCT image is consistent with that identified by the IOSI imaging, indicating the phase change in the OCT signals may associate with the changes in the corresponding hemodynamics. In vivo localized tissue dynamics in the barrel cortex at depth during whisker stimulation is observed and monitored in this study.

OCT intensity and phase fluctuations correlated with activity-dependent neuronal calcium dynamics in the Drosophila CNS [Invited

Phase-resolved OCT and fluorescence microscopy were used simultaneously to examine stereotypic patterns of neural activity in the isolated Drosophila central nervous system. Both imaging modalities were focused on individually identified bursicon neurons known to be involved in a fixed action pattern initiated by ecdysis-triggering hormone. We observed clear correspondence of OCT intensity, phase fluctuations, and activity-dependent calcium-induced fluorescence.

GPU accelerated real-time multi-functional spectral-domain optical coherence tomography system at 1300nm

We present a GPU accelerated multi-functional spectral domain optical coherence tomography system at 1300nm. The system is capable of real-time processing and display of every intensity image, comprised of 512 pixels by 2048 A-lines acquired at 20 frames per second. The update rate for all four images with size of 512 pixels by 2048 A-lines simultaneously (intensity, phase retardation, flow and en face view) is approximately 10 frames per second. Additionally, we report for the first time the characterization of phase retardation and diattenuation by a sample comprised of a stacked set of polarizing film and wave plate. The calculated optic axis orientation, phase retardation and diattenuation match well with expected values. The speed of each facet of the multi-functional OCT CPU-GPU hybrid acquisition system, intensity, phase retardation, and flow, were separately demonstrated by imaging a horseshoe crab lateral compound eye, a non-uniformly heated chicken muscle, and a microfluidic device. A mouse brain with thin skull preparation was imaged in vivo and demonstrated the capability of the system for live multi-functional OCT visualization.

Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation

We present fiber-based polarization-sensitive swept-source optical coherence tomography (SS-OCT) based on continuous source polarization modulation. The light source is a frequency swept laser centered at 1.31 microm with a scanning rate of 20 kHz. The incident polarization is modulated by a resonant electro-optic modulator at 33.3 MHz, which is one-third of the data acquisition frequency. The zeroth- and first-order harmonic components of the OCT signals with respect to the polarization modulation frequency have the polarimetric information of the sample. By algebraic and matrix calculations of the signals, this system can measure the depth-resolved Jones matrices of the sample with a single wavelength scan. The phase fluctuations of the starting trigger of wavelength scan and the polarization modulation are cancelled by monitoring the OCT phase of a calibration mirror inserted into the sample arm. We demonstrate the potential of the system by the measurement of chicken breast muscle and the volumetric measurement of an in vivo human anterior eye segment. The phase retardation image shows an additional contrast in the fibrous tissue such as the collagen fiber in the trabecular meshwork and sclera.