Huan-Jang Huang

Polarization-sensitive optical coherence tomography for imaging human atherosclerosis

Polarization-sensitive optical coherence tomography (PS-OCT) combines the advantages of OCT with image contrast enhancement, which is based on its ability to detect phase retardation and the fast-axis angle. Both PS-OCT images and histopathology have demonstrated similar features that allowed differentiation of atherosclerotic structures (i.e., plaques) from normal tissue. Moreover, the picrosirius polarization method was used to confirm PS-OCT assessment of collagen in the fibrous cap of atherosclerotic plaques, and high-frequency (40 MHz) ultrasound images were used to identify calcium in the vessel wall. Our preliminary ex vivo investigation of human aortic specimens indicated that PS-OCT might help to identify atherosclerotic lesions.

Imaging of human aortic atherosclerotic plaques by polarization-sensitive optical coherence tomography

Optical coherence tomography (OCT) is analogous to ultrasound imaging except that it uses infrared light instead of sound. Polarization-sensitive optical coherence tomography (PS-OCT) combines the advantages of OCT and provides additional image contrast of the tested sample. We demonstrate this technique for imaging of back-reflected light, birefringence, and fast-axis orientation simultaneously in different kinds of atherosclerosis plaque. This in vitro study suggests birefringence changes in plaque are due to the prominent deposition of collagen or cholesterol by correlating PS-OCT images with histology. Thus the combination of high resolution structural imaging and birefringence detection make PS-OCT a potentially powerful tool for early assessment of atherosclerosis appearance and prediction of plaque rupture.

Analog differential-phase detection in optical coherence reflectometer

A novel differential-phase optical coherence reflectometer (DP-OCR) was proposed using a low-coherence source, integrating it with an analog differential-phase decoding method. In the experiment, the DP-OCR performed a localized surface profile measurement of an optical grating (1200 lp/mm) and demonstrated its ability to measure the translation speed of a tilted mirror. Experimentally, the resolution of the axial displacement of proposed DP-OCR at 185 pm was demonstrated.

Polarized photon-pairs confocal laser scanning microscope

The abilities of reducing spherical aberration and enhancing image contrast of a polarized photon-pairs confocal laser scanning microscope (PCLSM) have been investigated. The axial responses of PCLSM are compared with that of CLSM.

Differential-phase optical coherence reflectometer for surface profile measurement

We developed a novel differential-phase optical coherence reflectometer (DP-OCR) by using a low-coherence light source and integrated with differential phase detection technique on surface profile measurement. In this setup, 2Å on detection of axial displacement was demonstrated. Thus, a localized surface profile was measured precisely by scanning an optical grating surface in this measurement. Moreover, the requirement on equal amplitude of the reference and signal beams of this novel reflectometer is discussed.

Spherical aberration cancellation in a polarized photon-pairs confocal laser scanning microscope

Refractive-index mismatch in conventional confocal microscopy produces severe degradation on axial resolution of sectioning image because the spherical aberration is generated in specimen. In this study, we propose a polarized photon-pairs confocal laser scanning microscope (PCLSM) in which a two-frequency linear polarized photon-pairs (LPPPs) laser beam is produced. The common-path propagation of LPPPs integrated with optical heterodyne technique not only can reduce the spherical aberration but also decreases scattering effect in specimen at same time. Therefore, the better axial and lateral resolutions of the sectioning image are produced simultaneously. In the experiment, a verification and comparison between PCLSM and conventional confocal laser scanning microscope (CLSM) on the ability of cancellation of spherical aberration induced by cover glass are demonstrated experimentally. Finally, the ability of PCLSM which can decrease the spherical aberration based on the common-path propagation of LPPPs associated with polarization gating, spatial coherence gating and spatial filtering gating is discussed.

Development of Linearly Polarized Optical Coherence Tomography and the measurement on Porcine Tendon Birefringence

A novel polarization-sensitive optical coherence tomography (PS-OCT) using only linearly polarized light is proposed. To compare with conventional PS-OCT which use circular polarized incident light, linear PS-OCT shows three advantages: (1) in a turbid medium with linear birefringence, the degree of polarization of backscattered light for linearly incident light dose not change significantly; (2) phase retardation (PR) of the sample can be obtained totally from the phase-difference between the polarization heterodyne signals, thus common phase noise rejection mode is introduced inherently. These advantages lead to the immunity of background phase noise and laser frequency noise simultaneously, and also lead to the better sensitivity of PR measurements; (3) the dynamic range of PR in this system is between 0deg to 180deg, which is two times larger than that of conventional circular PS-OCT

Comparative study of linearly and circularly polarized light in polarization-sensitive optical coherence tomography

We report a method for extracting the birefringence properties of samples with a novel proposed polarization-sensitive optical coherence tomography (PS-OCT) using linearly polarized incident light.