Biomedical subjects

Chia-Wei Sun

Publications and source records attributed to Chia-Wei Sun.

7 recordsLinked to original sources

PubMed2003

Optical imaging based on time-resolved Stokes vectors in filamentous tissues.

Time-resolved Stokes vector components of light transmitted through filamentous tissues were measured with a view to improving the imaging quality of optical images in such tissues. Temporal profiles of the Stokes vectors and the time-resolved degree of polarization (DOP) were calibrated to produce higher image quality than that of images based on time gating, polarization discrimination, or both. A thin chicken bone inserted into chicken breast tissue with filament orientation in different directions with respect to the direction of input linear polarization was scanned to demonstrate images of higher spatial resolution and contrast based on the measurement of time-resolved DOP.

Animals↗

PubMed2003

Resolution improvement with dispersion manipulation and a retrieval algorithm in optical coherence tomography.

We propose and demonstrate what is to our knowledge a novel technique of improving the spatial resolution of an optical coherence tomography (OCT) system given a non-Gaussian light source spectrum. By using dispersive materials in the reference arm of the OCT system, the resultant dispersion variation led to a full-width at half maximum (FWHM) of the interference fringe envelope smaller than the Fourier transform-limited value of a Gaussian spectral shape with the same spectral FWHM, at the expense of significant tails. The effects of the tails, which would blur the OCT images, were tremendously reduced with a retrieval algorithm. Simulation results and processed OCT scanning images have shown the capability of the proposed technique.

Journal Article↗

PubMed2003

Determination of the depth of a scattering target in a turbid medium with polarization discrimination of transmitted signals.

We demonstrate the feasibility of a novel method of determining target depth in a turbid medium through Monte Carlo simulations and experiments. The method is based on the strong and weak dependencies of the copolarized component and the degree of polarization (DOP), respectively, of the transmitted intensity on the target depth. The two-way measurements of the copolarized intensity can be used for determination of target depth, whereas the transversely scanned DOP results are used for estimating the two-dimensional image in a turbid system. The combination of these two sets of data could provide useful results for estimating three-dimensional images.

Journal Article↗

PubMed2003

Polarized light propagation through scattering media: time-resolved Monte Carlo simulations and experiments.

A study of polarized light transmitted through randomly scattering media of a polystyrene-microsphere solution is described. Temporal profiles of the Stokes vectors and the degree of polarization are measured experimentally and calculated theoretically based on a Monte Carlo technique. The experimental results match the theoretical results well, which demonstrates that the time-resolved Monte Carlo technique is a powerful tool that can contribute to the understanding of polarization propagation in biological tissue. Analysis based on the Stokes-Mueller formalism and the Mie theory shows that the first scattering event determines the major spatial patterns of the transmitted Stokes vectors. When an area detected at the output surface of a turbid medium is circularly symmetrical about the incident beam, the temporal profile of the transmitted light is independent of the incident polarization state. A linear relationship between the average order of the scatters and the light propagation time can be used to explain the exponential decay of the degree of polarization of transmitted light.

Algorithms↗

PubMed2003

Determination of target depth in a turbid medium with polarization-dependent transmitted signals.

We demonstrate a novel method for target depth determination in a turbid medium with experiments and Monte Carlo simulations. This method relies on the strong dependence of transmitted co-polarized intensity on target depth. Such a dependence originates from the inclusion of certain diffuse photons in the co-polarized intensity. A target of stronger scattering located closer to the transmitter results in stronger photon divergence and hence weaker co-polarized intensity at the receiver of a finite aperture. On the other hand, the degree of polarization (DOP) carries only information about ballistic and snake photons. It is weakly dependent on the target depth. The DOP data can be used as a reference of absolute scattering strength in the turbid system. Our experimental and Monte Carlo simulation results show the feasibility of the proposed target depth determination method. Meanwhile, it is shown that an appropriate time-gating process could help in improving the accuracy of target depth. In addition, the results show that the proposed method has quite large applicable ranges of scattering coefficient and absorption coefficient.

Journal Article↗

PubMedDate not supplied

Optical mapping of myocardial reactive oxygen species production throughout the reperfusion of global ischemia.

Reactive oxygen species (ROS) are short-lived, highly reactive chemical entities that play significant roles in all levels of biology. However, their measurement requires destructive preparation, thereby limiting the continuous measurement of ROS in a living tissue. We develop an optical mapping system to visualize ROS production in an isolated and perfused rat heart. By staining the heart with dihydroethidium (DHE), a 532-nm laser beam is directed to the epicardial surface, where we collect the red fluorescence (>600 nm) for semiquantitative analysis. With this system, ROS production as well as ventricular pressure and ECG in isolated perfused rat hearts are monitored throughout the reperfusion of global ischemia. Ischemia would decrease myocardial ROS production, while reperfusion would immediately result in sustained ROS overproduction. Optical mapping would provide information regarding the spatial distribution and temporal evolution of myocardial ROS production, which would enhance knowledge of the role of free radicals in cardiovascular biology.

Animals↗

PubMedDate not supplied

Myocardial tissue characterization based on a polarization-sensitive optical coherence tomography system with an ultrashort pulsed laser.

A polarization-sensitive optical coherence tomography (PSOCT) system using a femtosecond-laser as the broadband light source is implemented with the axial resolution of 5 microm in free space. Through the design of path-length difference between the two polarization inputs and the modulation of one of the polarization inputs, the PSOCT images of various input and output polarization combinations can be distinguished and simultaneously collected. The PSOCT system is then used for in vitro scanning of the myocardium tissues of normal and infarcted rat hearts. The destruction of the birefringence nature of the fiber muscle in the infarcted heart can be clearly observed.

Animals↗