Wen-Chuan Kuo

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.

Characteristics of a paired surface plasma waves biosensor.

A novel paired surface plasma wave biosensor (PSPWB) is described and setup. By integrating the features of a common-path optical heterodyne interferometer and the amplitude-ratio detection mode, the PSPWB not only produces a high detection sensitivity but also provides a large dynamic measurement range for effective refractive index (Deltan(eff)) based on amplitude-sensitive detection method. Thus, the performance of PSPWB becomes equivalent to shot-noise limited of a conventional SPR biosensor. To our knowledge, this novel PSPWB shows the highest detection sensitivity on (Deltan(eff)) when compared with conventional SPR biosensors using either a non-interferometric or interferometric technique. The experimental results correctly verify the properties of a PSPWB that the detection sensitivity is an order of 10(-7) refractive index unit (RIU) when measuring a 0.001% sucrose-water solution. This result confirms the detection sensitivity up to 10(-9) RIU of the IgG/anti-IgG interaction in real time successfully. Furthermore, a dynamic range of 10(5) using PSPWB was also obtained.

Assessment of arterial characteristics in human atherosclerosis by extracting optical properties from polarization-sensitive optical coherence tomography.

In this research, we assessed arterial characteristics in human atherosclerosis by determining both scattering and birefringence properties of vessel tissue from polarization-sensitive optical coherence tomography (PS-OCT) images. We demonstrated that optical characteristics including scattering coefficient (mu(s)), effective anisotropy factor (g(eff)), birefringence coefficient (Delta n), and fast-axis angle (beta) of normal and different kinds of atherosclerotic lesions in human vessels can be quantitatively described. Based on our findings, a quantitative PS-OCT image criterion for plaque characterization was constructed.

DIAGNOSIS OF ARTICULAR CARTILAGE DAMAGE BY POLARIZATION SENSITIVE OPTICAL COHERENCE TOMOGRAPHY AND THE EXTRACTED OPTICAL PROPERTIES

This paper presents a diagnosis method for articular cartilage damage using polarization-sensitive optical coherence tomography (PS-OCT). Through signal analysis, the optical characteristics of intact cartilage and different types of mild lesions within cartilages can be quantified from measures such as the scattering coefficient (μs), effective anisotropy factor (geff ), and birefringence coefficient (Δn). Our preliminary investigation using porcine articular cartilage indicated that both subsurface morphological changes and apparent variations in optical properties, which may be the early signs of cartilage degeneration, were found in three types of diseased cartilages.

Simultaneous Measurement of Phase Retardation and Fast-Axis Angle of Phase Retardation Plate

A phase retardation plate, such as a quarter-wave plate, is able to control the state of polarization. Thus, a precise simultaneous determination of phase delay between two eigen-polarization states and its fast-axis angle is essential to the performance of the phase retardation plate to control the state of polarization. Consequently, the measurement of the two-dimensional spatiotemporal distribution of phase retardation and the fast-axis angle become crucial when a large-area of phase retardation plate, such as that for a liquid crystal display, is characterized, due to the inhomogeneity of the retardation plate. In order to measure the linear birefringence parameters, phase retardation and fast-axis angle at the same time, a novel polarized optical heterodyne interferometer is developed, with which the parameters of a quarter-wave plate are successfully measured and verified. The features of this device are (1) a common-path configuration, (2) measurement independent of laser intensity, and (3) the capability of simultaneously determining the spatiotemporal distributions of phase retardation and fast-axis angle of a retardation plate.

Cell parameter measurement of a twisted nematic liquid crystal device using interferometric polarimeter under normal incidence

Five cell parameters of a twisted nematic liquid crystal device (TNLCD), namely, cell gap, pretilt angle, twisted angle, rubbing angle, and phase retardation are precisely measured by the developed amplitude-sensitive heterodyne polarimeter (ASHP) simultaneously integrated with Yeh and Gus transfer matrix and Liens transfer matrix. This proposed method can characterize the five cell parameters under the arrangement of a single wavelength at normal incidence. In contrast to the conventional methods on cell parameter detection either by adopting a multiple wavelength laser beam at normal incidence or by using a single wavelength laser beam under oblique incident to TNLCD, this method presents the advantage of not only having a simple setup but also the possibility to measure simultaneously five cell parameters on the characterization of TNLCD at high speed.

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.

Quantitative analysis on optical properties of human atherosclerosis by using polarization-sensitive optical coherence tomography

In this research, we have used an algorithm to extract four different optical parameters, including the scattering coefficient (μs), effective anisotropy factor (goff), birefringence coefficient (Δn), and fast-axis angle (β) from polarization-sensitive optical coherence tomography (PS-OCT) images. The proposed method was evaluated from a set of phantoms and it yielded valid results. We demonstrate that the optical characteristic of normal and different kinds of atherosclerotic lesions in human vessel can be quantitatively described. Whether change in these quantified optical properties could be used to discriminate between different types of human atherosclerotic plaques was examined.

Exploring the mechanism of radiation-enhanced hepatocellular carcinoma cell invasion by swept source optical coherence tomography

Ionizing radiation is a standard treatment for various human solid tumors. However, several clinical studies showed that a significant proportion of patients undergoing radiotherapy for hepatocellular carcinoma (HCC) develop intrahepatic and extrahepatic metastasis. Understanding of radiation-induced cancer cell invasiveness and behavior is essential and of great important for developing suitable treatment strategies to contain cancer spread. Therefore, in this study we evaluated the effectiveness of using swept source optical coherence tomography (SS-OCT) to monitor the enhancement of HCC cell invasiveness by radiation. SS-OCT images were acquired and recorded to obtain three-dimensional data sets per four hours in 48 hours after irradiating HepG2 cells with 7.5 Gy. The cell migration behavior in three-dimensional tissue models was quantified from images of radiation-induced and sham-irradiated cells.

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.