Chih-Wei Lu

Measurement of the hemoglobin oxygen saturation level with spectroscopic spectral-domain optical coherence tomography

We report the measurement of the hemoglobin (Hb) oxygen saturation level in human blood with a spectroscopic spectral-domain optical coherence tomography (SSD-OCT) system based on the crossover behavior of Hb and oxyhemoglobin (HbO(2)) absorption coefficients around 800 nm. By calculating the ratio of the exponential decay constant of A-mode scan signal in the long-wavelength range (>800 nm) over that in the short-wavelength range (<800 nm), the relative oxygen saturation level of Hb can be calibrated. Such a relative level can be used for practical diagnosis application after a golden standard is built by comparing the variation of the OCT result with that of a conventional method, such as the use of a blood gas analyzer. In our experiment, the variation curve based on the SSD-OCT measurement, which has the advantages of noninvasive, real-time, and high-resolution measurements, is coincident with that of using a commercial blood gas analyzer.

Delineation of an oral cancer lesion with swept-source optical coherence tomography

We demonstrate the ex vivo imaging of an oral cancerous sample with a swept-source optical coherence tomography (SS-OCT) system. With the axial resolution of 8 microm in free space and system sensitivity of 108 dB, we can well distinguish the normal and abnormal tissue portions in a sample. In particular, we analyze the lateral variation of A-scan profiles to show two parameters of SS-OCT signal for delineating an oral cancer lesion. One of the parameters is the decay constant in the exponential fitting of the SS-OCT signal intensity along depth. This decay constant decreases as the A-scan point moves laterally across the margin of a lesion. The other parameter is the standard deviation of the SS-OCT signal intensity fluctuation in an A-scan. This parameter increases significantly when the A-scan point is moved across the transition region between the normal and abnormal portions. Such parameters are useful for determining the margins of oral cancer.

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.

Subgingival calculus imaging based on swept-source optical coherence tomography

We characterized and imaged dental calculus using swept-source optical coherence tomography (SS-OCT). The refractive indices of enamel, dentin, cementum, and calculus were measured as 1.625 ± 0.024, 1.534 ± 0.029, 1.570 ± 0.021, and 2.097 ± 0.094, respectively. Dental calculus leads strong scattering properties, and thus, the region can be identified from enamel with SS-OCT imaging. An extracted human tooth with calculus is covered with gingiva tissue as an in vitro sample for tomographic imaging.

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.

Oral Cancer Diagnosis with Optical Coherence Tomography

We use an optical coherence tomography system with a specially designed probe to image the structures of tissues within the oral cavity for the diagnosis of oral precancer and cancer. Various types of oral mucosa, such as gingiva and buccal mucosa, normal and abnormal, can be well distinguished

Diffuse Optical Multipatch Technique for Tissue Oxygenation Monitoring: Clinical Study in Intensive Care Unit

Diffuse optical multipatch technique is used to assess spatial variations in absorption and scattering in biological tissue, by monitoring changes in the concentration of oxyhemoglobin and deoxyhemoglobin. In our preliminary study, the temporal tracings of tissue oxygenation are measured using diffuse optical multipatch measurement and a venous occlusion test, employing normal subjects and ICU patients suffering from sepsis and heart failure. In experiments, obvious differences in tissue oxygenation signals were observed among all three groups. This paper discusses the physiological relevance of tissue oxygenation with respect to disease.

Comparisons of the transmitted signals of time, aperture, and angle gating in biological tissues and a phantom

We measure transmitted signals with time, aperture, and angle gating for comparison in micro-sphere suspension, chicken breast and chicken liver tissues. We find that in each sample, the small aperture-gated (angle-gated) signals for imaging are essentially different from those of early time gating. Meanwhile, the signals obtained from aperture and angle gating come from quite different parts of the transmitted photons. For biological tissues of different structures, different gating methods may lead to different levels of imaging quality. Also, the results indicate the generally different scattering characteristics of biological tissues from that of a particle-based phantom. The scattering nature in the biological tissues may imply that random continuum scattering needs to be considered in biological imaging. Between chicken breast and liver tissues, the time-gated data show that the later has stronger scattering and absorption.

Optical coherence tomography using nonlinear optics in fiber for broadband source generation

An optical coherence tomography (OCT) system of sub-10-μm resolution, with its broadband source generated through nonlinear optics processes of a femtosecond Ti:sapphire laser in a single-mode fiber, was built for biological tissue scanning. With 400 mW power coupled into the fiber, a spectral full-width-at-half-maximum (FWHM) of 46 nm, centered at 840 nm, could be obtained. The available power for sample illumination could be as high as 100 mW. This condition was used to achieve the OCT depth resolution of 8.6 μm in tissues. The OCT system was used for scanning a human gingival mucosa sample. Cavity structures were observed that were quite consistent with the results of histological examination.

Polarization-dependent characteristics and polarization gating in time-resolved optical imaging of skeletal muscle tissues

The comparisons of the time-resolved transmitted intensity profiles and imaging results based on the polarization gating method between the samples of diluted milk, chicken breast tissue, and chopped chicken breast tissue revealed that the anisotropic structure of chicken breast tissue resulted in coherent coupling between the two inherent polarization directions and difficulty of using the polarization gating method for optical imaging through skeletal muscle tissues. To explore the polarization-dependent optical properties of chicken breast tissues, we calibrated the extinction coefficients of the polarization components parallel with and perpendicular to tissue filaments and the cross-polarized intensity-coupling coefficients between the two polarization components, based on the measured snake-photon intensity data. The calibrated values of these coefficients were quite consistent with previously reported. The extinction coefficient in the polarization along tissue filaments was significantly higher than that of the other polarization. Also, the cross-polarized coupling coefficient of the coupling from the polarization of tissue filaments into the other was stronger than that of inverse coupling.