This paper presents a hand-held single-mode fiber-based polarization-sensitive optical coherence tomography (PS-OCT) system with a single input polarization state. One drawback of this system is that the polarization becomes arbitrary, which can be solved by placing a polarization controller in the sample arm. A calibration target with an azimuthally varying optic axis integrated with the handheld probe will provide an absolute orientation axis measurement. This significantly reduces cost, time and availability of PS-OCT for clinical applications. With the home-built PS-OCT, we investigate the reorganization of collagen and blood vessel in a wound on the dorsal side of the human hand.
A novel polarization state tracing algorithm has been proposed to visualize depth-resolved birefringent information by using the polarization sensitive optical coherence tomography (PSOCT) system. This algorithm is compatible to the widely adopted single input PSOCT system which uses only one circularly polarized incident light. We demonstrate the ability of this method to visualize depth-resolved myocardial architecture in both healthy and infarcted rodent hearts (ex vivo) and collagen structures responsible for skin tension lines at various anatomical locations on the face of a healthy human volunteer (in vivo).
Reconstructive skin surgeries drive the clinical need for non-contact objective measurements of skin elasticity. Here we demonstrate that all three of skin’s elastic constants (in-plane and out-of-plane shear moduli and an additional modulus defining skin’s tensile anisotropy) and the orientation of collagen fibers in dermis can be determined from Rayleigh wave anisotropy in-plane with acoustic micro-tapping (AuT) OCE. A nearly-incompressible transverse isotropic (NITI) model was used to reconstruct skin’s moduli from OCE measurements in human forearm in vivo for five healthy volunteers. Co-registered polarization-sensitive (PS-) OCT shows that optical and mechanical axes are co-aligned at measured sites.
Using numerical and analytical models of wave propagation in mechanically anisotropic materials, we highlight the complications associated with quantitative estimates of mechanical moduli in human skin. To obtain reliable, quantitative measurements of moduli in human skin, multiple aspects of mechanical wave propagation in structures typical of skin must be considered. Using a nearly incompressible transverse isotropic (NITI) model, preliminary measurements of both shear moduli (G and μ) in healthy in vivo human skin are presented.
Significance: Our work advances the development of fiber-based polarization-sensitive optical coherence tomography (PS-OCT) by stabilizing the output polarization state of the light beam when the system is under environmental disturbance. While the fiber-based PS-OCT has been demonstrated previously, it remains a challenge for the traditional fiber-based PS-OCT to obtain a stable measurement when the optic fibers are disturbed by the environment. This important issue is addressed, paving the path for clinical translation of PS-OCT, which can provide a unique perspective of the biological samples.
Aim: Polarization maintaining common-path (CP) interferometer is fabricated with the goal of providing a stable fiber-based PS-OCT imaging system that is only responsive to the polarization changes generated by the sample, immune to environmental conditions.
Approach: The system is implemented by incorporating a CP interferometer together with polarization maintaining (PM) fibers. The PM fibers are used to preserve the two orthogonal linearly polarized components of the light during propagation. By sharing the CP in the sample and reference arms, any variations in phase retardation can be eliminated between the two channels in the PM fibers. The combination of the PM fiber and the CP interferometer ensures the stability of the output polarization state.
Results: The stability of the proposed PS-OCT system is tested when a periodically stressed disturbance is applied to the fibers within the system. Stable in vivo PS-OCT images of the mouse thigh are demonstrated.
Conclusions: We have demonstrated a stable fiber-based PS-OCT system that combined the PM fiber and the CP configuration together. We have shown that the output polarization states and the system sensitivity can keep stable over time under the environmental disturbances to the system.
Significance: Cerebral blood flow (CBF) regulation at neurovascular coupling (NVC) plays an important role in normal brain functioning to support oxygen delivery to activating neurons. Therefore, studying the mechanisms of CBF adjustment is crucial for the improved understanding of brain activity.
Aim: We investigated the temporal profile of hemodynamic signal change in mouse cortex caused by neural activation and its variation over cortical depth.
Approach: Following the cranial window surgery, intrinsic optical signal imaging (IOSI) was used to spatially locate the activated region in mouse cortex during whisker stimulation. Optical microangiography (OMAG), the functional extension of optical coherence tomography, was applied to image the activated and control regions identified by IOSI. Temporal profiles of hemodynamic response signals obtained by IOSI and OMAG were compared, and OMAG signal was analyzed over cortical layers.
Results: Our results showed that the hemodynamic response to neural activity revealed by blood flow change signal signal through IOSI is slower than that observed by OMAG signal. OMAG also indicated the laminar variation of the response over cortical depth, showing the largest response in cortical layer IV.
Conclusions: Overall, we demonstrated the development and application of dual-modality imaging system composed of IOSI and OMAG, which may have potential to enable the future investigations of depth-resolved CBF and to provide the insights of hemodynamic events associated with the NVC.
A novel stable fiber-based multi-functional imaging system capable of simultaneously acquiring the birefringent and polarization artifact-free microvascular information within scanned tissue volume is demonstrated. A novel system design that can compensate for the changes in polarization state generated by the optics fibers is introduced to stabilize the imaging system. The proposed system is employed to visualize the birefringent components and the vasculature networks of the human skin in vivo.
We propose a novel method to visualize the integrated birefringence information for polarization-sensitive optical coherence tomography (PS-OCT) of biological tissue. A strategy that integrates the comprehensive birefringence property in a resultant image is introduced to obtain high contrast images of the birefringent samples. Then, color-based automatic segmentation of birefringent components from 3D scanned tissue volume is proposed to isolate the 3D network of the nerve bundles in a whole mouse brain. Experimental validation and demonstrations are given by imaging ex vivo mouse tail and whole brain tissues to show the usefulness of proposed comprehensive birefringent imaging and segmentation methods. These results sufficiently demonstrate the practical usefulness of the proposed strategy of using comprehensive polarization as the imaging parameter in the PS-OCT imaging of biological samples, indicating potential applications in both pre-clinical and clinical environments where accurate identification of birefringent tissue components is important, for example the nerve identification in delicate surgical remove of the diseased tissue mass in surgery.
The dynamic properties of subcellular organism are important biomarkers of health. Imaging subcellular level dynamics provides effective solutions for evaluating cell metabolism, and moreover, testing the responses of cells to pathogens and drugs in pharmaceutical engineering. In this paper, we demonstrate an innovative approach to contrast the subcellular motions by using eigen decomposition (ED) based variance analysis of time-dependent complex optical coherence tomography (OCT) signals. This method reveals superior contrast to noise advantage compared with intensity-based dynamic imaging regime. Further validation experiments were performed with B-mode imaging sections crossing a wide range of sampling frequencies, and on the patterned samples of yeast powder mixed with gelatin/TiO2-water solution. In addition, the proposed method was further used to image mouse cerebral cortex in vivo, suggesting the promising of ED based correlation power mapping in analyzing coupled dynamics of neuron activity and cerebral blood flow. The proposed technique promises efficient measurement of subcellular motions with high sensitivity and low artifact involvement, suggesting high potential for in vivo and in situ applications.
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