Yih-Ming Wang

Effective indicators for diagnosis of oral cancer using optical coherence tomography

A swept-source optical coherence tomography system is used to clinically scan oral precancer and cancer patients for statistically analyzing the effective indicators of diagnosis. Three indicators are considered, including the standard deviation (SD) of an A-mode scan signal profile, the exponential decay constant (alpha) of an A-mode-scan spatial-frequency spectrum, and the epithelium thickness (T) when the boundary between epithelium and lamina propria can still be identified. Generally, in abnormal mucosa, the standard deviation becomes larger, the decay constant of the spatial-frequency spectrum becomes smaller, and epithelium becomes thicker. The sensitivity and specificity of the three indicators are discussed based on universal and individual relative criteria. It is found that SD and alpha are good diagnosis indicators for moderate dysplasia and squamous cell carcinoma. On the other hand, T is a good diagnosis indicator for epithelia hyperplasia and moderate dysplasia.

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.

Differentiating oral lesions in different carcinogenesis stages with optical coherence tomography

A swept-source optical coherence tomography (SS-OCT) system is used to clinically scan oral lesions in different oral carcinogenesis stages, including normal oral mucosa control, mild dysplasia (MiD), moderate dysplasia (MoD), early-stage squamous cell carcinoma (ES-SCC), and well-developed SCC (WD-SCC), for diagnosis purpose. On the basis of the analyses of the SS-OCT images, the stages of dysplasia (MiD and MoD), and SCC (ES-SCC and WD-SCC) can be differentiated from normal control by evaluating the depth-dependent standard deviation (SD) values of lateral variations. In the dysplasia stage, the boundary between the epithelium (EP) and lamina propria (LP) layers can still be identified and the EP layer becomes significantly thicker than that of normal control. Also, in a certain range of the EP layer above the EP/LP boundary, the SD value becomes larger than a certain percentage of the maximum level, which is observed around the EP/LP boundary. On the other hand, in the ES-SCC and WD-SCC stages, the EP/LP boundary disappears. Because of the higher density of connective tissue papillae in the ES-SCC stage, the SD values of the slowly varying lateral scan profiles in the ES-SCC samples are significantly larger than those in the WD-SCC sample. Also, ES-SCC can be differentiated from WD-SCC by comparing the exponential decay constants of averaged A-mode scan profiles. Because of the higher tissue absorption in the WD-SCC lesion, the decay constants in the WD-SCC samples are significantly higher than those in the ES-SCC samples.

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.

Diagnosis of oral submucous fibrosis with optical coherence tomography

The epithelium (EP) thickness and the standard deviation (SD) of A-mode scan intensity in the laminar propria (LP) layer are used as effective indicators for the diagnosis of oral submucous fibrosis (OSF) based on the noninvasive clinical scanning of a swept-source optical coherence tomography (OCT) system of approximately 6 mum in axial resolution (in tissue) and 103 dB in sensitivity. Compared with the corresponding parameters in healthy oral mucosal mucosa, in OSF mucosa, the EP thickness becomes smaller and the SD of A-mode scan intensity in the LP layer (LP SD) also becomes smaller. The LP SD can also be used for effectively differentiating OSF (small LP SD) from lesion (large LP SD). This application is particularly useful in the case of a lesion without a clear surface feature. Meanwhile, the use of the SD of A-mode scan intensity in the EP layer (EP SD) can further help in differentiating OSF (medium EP SD) from healthy oral mucosal (small EP SD) and lesion (large EP SD) conditions. Compared with the conventional method of maximum mouth opening measurement, the use of the proposed OCT scanning results can be a more effective technique for OSF diagnosis.

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.

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

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.

Tissue birefringence of hypercholesterolemic rat liver measured with polarization-sensitive optical coherence tomography.

We measure in vitro tissue birefringence in the liver of hypercholesterolemic rats with polarization-sensitive optical coherence tomography. Tissue birefringence is determined by measuring the phase retardation as a function of tissue depth. The birefringence of such a sample is usually due to the narrow fibrous structures that cannot be resolved by a standard optical coherence tomography system. Anisotropic structures are formed in the hypercholesterolemic rat liver, which is quite different from the isotropic nature of healthy liver. Birefringence is evaluated to give an order of magnitude of 4.48x10(-4) at 790 nm in hypercholesterolemic rat liver. The infiltration of macrophages and increased collagen deposition should be major causes for tissue birefringence in hypercholesterolemic liver.

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.