Teck-Chee Chia

Laser-induced autofluorescence of human colonic tissues

The purpose of this study is to perform a preliminary evaluation of the diagnostic potential of laser-induced autofluorescence spectroscopy for colonic tumors using fluorescence intensity ratios at specific wavelengths. Measurements were made on normal mucosa and adenocarcinoma of human colon tissues. Each tissue section was examined using an optical probe consisting of a central fiber for delivering the excitation laser and a fiber bundle for detection of the fluorescence. Using different wavelengths of a CW mixed-gas laser, we measured and analyzed the LIAF spectra of tissues through a polychromator coupled with a CCD detector. It can be found that in the range of 520-620 nm, the spectral shapes of tumor tissues are very similar to the normal tissue spectra, and the autofluorescence intensities of normal tissues are about threefold higher than those of tumor tissues. However, in the range of 625- 720nm, the autofluorescence intensities of tumor tissues are higher than those of normal tissue. The spectral characteristics peaks arising from endogenous porphyrins can be observed in some tumor tissues. The preliminary results show that the autofluorescence intensity ratio of I580/I630 or I580/I680 can be used to distinguish colonic tumors from normal tissues with good accuracy.

Laser-induced microscopic fluorescence and images of skin tissues

The microscopic autofluorescence and images of different tissue layer in normal and cancerous skin tissues were studied under a micro spectrophotometric system when using a laser light at 442 nm. The results show that the autofluorescence images of normal skin tissues are much brighter than the cancerous ones, and the autofluorescence intensity from various tissue layers of normal skin is stronger than that of cancerous skin tissues. It is also found that the dermis emits more intense fluorescence while epidermis fluoresces weakly in the skin tissues. The obtained data on the microscopic fluorescence properties in the skin will be useful to aid in the interpretation of underlying mechanisms by which the laser-induced autofluorescence technique differentiates between normal and cancerous skin tissues.

Changes in autofluorescence emission intensities of human colonic tissues due to photobleaching process

Changes in autofluorescence intensities at 550, 580, 680 and 720 nm as functions of incident intensity and exposure time were measured in normal mucosa and adenocarcinomatous of human colonic tissues when excited by the wavelengths of 457.9, 488, 514.5 and 632.8 nm, respectively. The obtained results show that the photobleaching process of the autofluorescence follows a double-exponential function. The slower decay rates of the photobleaching at 550 and 580 nm emissions could be found in normal tissues compared to those in tumor tissues, however, the faster decay times at 680 and 720 nm emissions were also found in normal tissues. It appears that the quantitative measurements of photobleaching processes may provide a method to evaluate the fractional contribution of the autofluorescence from different layers in the colon tissues. The evaluation of temporal behavior of photobleaching processes of autofluorescence emissions may also reveal the different accumulated concentrations of endogenous fluorophores between normal and tumor tissues.

Laser-induced fluorescence microscopy of human lung tissues

Early detection of lung cancer has been a significant area of interest due to the large number of cancer-related deaths. The microscopic fluorescence and imaging of excised lung tissue sections were studied using a novel microspectrophotometric system. The intrinsic autofluorescence distributions in different tissue layers of the lung were observed in normal and malignant tissues. The preliminary results show that the microscopic fluorescence analysis on different tissue layers can provide a powerful means to explore the origin of spectral differences between normal and abnormal lung tissues.

Principles and techniques for measuring optical parameters of biotissue

In this paper, the principles of light propagation in tissue and techniques for measuring the optical parameters of tissues are briefly described. A new approach to measure optical parameters has been developed. We combine the solution of the diffusion theory with a result of Monte Carlo simulation to calculate the optical parameters of several mammalian tissue. This indirect approach might be used to determine the optical properties of human tissue. In addition, we also believe that the refractive index of bio- tissue is another important optical parameter in tissue optics. Recently, we have developed a new simple method based on total-internal-reflection to measure the refractive index of tissue. The main advantages of the method are its elimination of multiscattering effects, suitability to a small sample, and excellent accuracy of measurement. The refractive indices of skin from people of different age, sex and skin color in vivo was recently measured. We believe that it is the first set of data of index of refraction of human tissue in vivo.

Comparison of human colorectal normal tissue with cancerous tissue autofluorescence image by optical sectioning with a confocal laser-scanning microscope

We investigated normal and cancerous human colorectal tissues (fresh thick biopsy specimens) using Olympus Confocal laser scanning biological microscope (FV300). The different layers of autofluorescence images of the specimen were captured by 488 nm laser scanning and sectioning. Optical sectioning can be performed in the vertical plane. Laser scanning can be performed in the horizontal plane. By comparing the autofluorescence image of the normal colorectal tissue with cancerous tissue, the structures of the optical sectioning image layer were found to be significantly different. We have also obtained fibrous autofluorescence image inside tissue specimen. Our investigation may help provide some useful insight to other autofluorescence research studies like laser induced autofluorescence spectra of human colorectal tissue study as a diagnosis technique for clinical application.

Laser-induced fluorescence spectrum of human colonic tissues by Monte Carlo modeling

Based on the microscopic properties of colonic tissues, a five-layer colon optical model was developed to calculate the excitation light distribution in the tissue and the fluorescence escape function from the tissue by Monte Carlo simulations. The theoretically modeled fluorescence spectrum fits well to the experimental results, demonstrating that the microscopic properties of tissue applied in the colon optical model can be quantitatively correlated with the macroscopic autofluorescence measurements.

Detection of colorectal cancer using time-resolved autofluorescence spectrometer

As we know Quantum mechanics is a mathematical theory that can describe the behavior of objects that are at microscopic level. Time-resolved autofluorescence spectrometer monitors events that occur during the lifetime of the excited state. This time ranges from a few picoseconds to hundreds of nanoseconds. That is an extremely important advance as it allows environmental parameters to be monitored in a spatially defined manner in the specimen under study. This technique is based on the application of Quantum Mechanics. This principle is applied in our project as we are trying to use different fluorescence spectra to detect biological molecules commonly found in cancerous colorectal tissue and thereby differentiate the cancerous and non-cancerous colorectal polyps more accurately and specifically. In this paper, we use Fluorescence Lifetime Spectrometer (Edinburgh Instruments FL920) to measure decay time of autofluorescence of colorectal cancerous and normal tissue sample. All specimens are from Department of Colorectal Surgery, Singapore General Hospital. The tissues are placed in the time-resolved autofluorescence instrument, which records and calculates the decay time of the autofluorescence in the tissue sample at the excitation and emission wavelengths pre-determined from a conventional spectrometer. By studying the decay time,τ, etc. for cancerous and normal tissue, we aim to present time-resolved autofluorescence as a feasible technique for earlier detection of malignant colorectal tissues. By using this concept, we try to contribute an algorithm even an application tool for real time early diagnosis of colorectal cancer for clinical services.

Study of the Intensity Ratio from the Characteristics of Autofluorescence Spectra of the Human Colorectal Tissue

Autofluorescence is widely investigated as a sensitive method in early diagnosis of diseased tissue, but most measurements of tissue autofluorescence were performed with only a single excitation wavelength. This work is aim to optimize the excitation wavelength or emission wavelength bands for fluorescence spectroscopy for better clinical diagnostic accuracy. The autofluorescence spectra of colorectal tissue were studied over a wide excitation range (350-600 nm). The excitation 350 nm and 470 nm were identified as effective excitation wavelength for inducing tissue autofluorescence. The ratio of emission peak intensity at 470 nm versus 610 nm excited by 350 nm and the ratio of emission peak intensity at 510 nm versus 610 nm excited by 470 nm were found as good indications to distinguish normal and diseased tissue. The observed peaks of the fluorescence spectra were also compared with some well known tissue fluorophores.

Autofluorescence diagnostic algorithm for detecting malignant colonic tissues

The ratio of autofluorescence intensity at 550+/- 10 nm to that at 630+/- 10 nm (R1=I550/I630) or 680+/- 10 nm (R2=I550/I680) was used as a diagnostic algorithm for identification of malignant tumour tissues. The performance of the ratio diagnostic algorithm was evaluated on more than 100 human colonic specimens under excitation laser light at 457.9 nm. A significant difference of the ratio value R1 and R2 was found between normal and tumour specimens (p<0.001). The diagnostic test has a sensitivity and specificity of 85% and 87% for a threshold value of R1=1.75, and a sensitivity and specificity of 94% and 82% for a threshold of R2=3.5. The experimental results show that the ratio mapping is sensitive to the small changes in the presence of tumour tissues, and the contrast of the contour map for detecting the region of malignancy can also be enhanced significantly if using the diagnostic algorithm R2 (I550/I680).