Han-Chao Chang

The pulse exciation of UV LED source for fluorescence detection

Fluorescence is widely used to detect the biochemical effect and some substance containing certain dye. In general, the formation of fluorescent reaction is that an organism or dye, excited by UV light (200–405 nm), emits a specific frequency of light; the light is usually a visible or near infrared light (405–900 nm) However, the object excited by continue UV light cannot provide the periodic response information and clear images for fluorescence analysis, and the fluorescence intensity of organism will decay with the time exposed to UV light. In this study, we use a tunable pulse control module to perform the fluorescence test of security organic dye, BL-ORT. When the BL-ORT is excited by the 30 ms/cycle pulsed UV-LED light, the most complete fluorescence datum can be obtained. Furthermore, the power consumption of pulsed exciting source can be down to 50 percent.

A study on oxygen saturation images constructed from the skin tissue of human hand

Under the irradiation of lights of two different wavelengths, the skin image of human hand can be obtained and roughly applied to construct the oxygen saturation image of skin tissue. The penetration (skin) depth of incident light increases with increasing wavelength between 350 to 1000 nm, and the deoxy-hemoglobin (Hb) and oxy-hemoglobin (HbO2) has a relatively high absorptivity in visible and near-infrared (NIR) spectrum, respectively; therefore, the intensity of diffuse reflected images of skin can be used to compute the oxygen saturation images of skin tissue. In the experiment, three LED light sources (red - 660 nm, NIR - 890 and 940 nm) were applied to construct the oxygen saturation images of skin tissue. The experiments show the oxygen saturation ranging from 84.69 to 88.79 % at the wrist and from 78.09 to 81.81 % at the back of hand when the skin tissue is irradiated by 660 and 890 nm LED light. The results not only could provide the distribution of oxygen saturation but also similar to the multi-spectral imaging method. In the future, the above result can be compared to that of transcutaneous oxygen pressure measurement (TcPO2), and provide a good reference to build the relationship between the oxygen saturation and healthy index for cardiovascular system in clinical diagnosis.

The image analysis of skin tissue irradiated with difference wavelengths of LED sources

Under the different light irradiation, the reflective and scattering intensity of skin image can be applied to evaluate many human health indices, such as oxygen saturation in blood, skin tissue aging or skin lesions (leukoplakia, turmoil cell, and so on). Due to the different absorption and scattering rate of skin illustrated by a variety of LED light source, we can perform the processing and analysis of skin surface images. Since the surface roughness is more sensitive to the shorter wavelength light source (430 nm and 470 nm LED), so the difference of reflective light image can be used to detect the skin roughness. In addition, the oxygenated hemoglobin (HbO2) in blood has a relatively high absorption rate at green (570 nm) and near-infrared (940 nm) light, so it can be used to compute the oxygen saturation. In this study, based on the different light absorption of HbO2 in blood, there are six light sources (deep blue, blue, green, deep red, NIR, white light) would be applied to the inspection of skin characteristics. The processed images provide better reference for the follow-up studies on the oxygen saturation of peripheral blood and skin aging.

Method to obtain the high contrast images of blood vessel for oxygen saturation calculation

The skin illuminated of two lights at different wavelength can be applied to detect the oxygen saturation of human blood. Due to the absorption coefficient of oxy- (HbO2) and deoxy- (Hb) hemoglobin are different at the wavelength 660 nm and 890 nm, the transmitted and reflected light within the skin can be used to compute the oxygen saturation image of skin. However, the intensities of skin images illuminated by a 20 mW NIR-LED are too low to determine the position of blood vessel when acquired by the color CCD camera. In order to improve the disadvantages, a mono camera was used and the irradiated distance and angle between LED light and test hand were adjusted to acquire the higher resolution and contrast blood vessel images for the oxygen saturation calculation. In the experiment, we developed the suitable angle to irradiate NIR light is at 75 degrees because the reflected and scattered effect could be generated significantly from both vertical and horizontal direction. In addition, the best contrast vessel images can be obtained when the shutter time is set at 44.030 ms and the irradiated distance was at the range 140-160 mm due to the intensity ratio between tissue and vessel region is the highest and the intensities of image would not be saturated or become too low when these two parameters were adjusted slightly. In future, the proposed parameters and results can be applied to the oxygen saturation measurement in the clinical diagnosis.

Optical imaging with spectrum aberration correction using a filtering macrolens

A filtering macrolens was developed to simultaneously achieve macro-optical imaging and correct spectrum aberration. The macrolens was a doublet lens comprising a filtering lens and a close-up lens. The shape of the filtering lens was designed to eliminate the optical path differences between the light rays in the absorbing medium. The close-up lens was designed to decrease the effective focal length of an ordinary camera lens to provide high magnification capability and collimate the diverging beams through the filtering lens. Experimental results demonstrated that the spectrum uniformity of the macro-optical images was markedly improved by the filtering macrolens. This innovation may be used in finite conjugate optical systems.

Accurate laser skin perforation technique aimed at promoting bleeding and reducing pain

Laser skin perforation is an effective and promising technique for use in blood collection. In this study, the relation between the perforation profile of skin and laser irradiation at various energies is discussed. Increasing laser energy does not uniformly expand the size and depth of a hole because the shallow depth of field (DOF) of the focused light primarily concentrates energy on the skin surface. In practice, the hole gradually transforms from a semielliptical shape to an upside-down avocado shape as the laser energy increases. This phenomenon can increase the amount of bleeding and reduce pain. The findings support the feasibility of developing an accurate laser skin perforation method.

Developing a dermatological photodiagnosis system by optical image analyses and in vivo study

Dermatological photodynamic therapy (DPDT) involves using systematic photosensitizers in combination with light irradiation treatment to eliminate cancer cells. Therefore, a noninvasive fluorescence photodiagnosis system is critical in DPDT for diagnosing target tissues and demarcating the margin of normal tissues. This study proposes a 375-nm ring LED light module in fluorescence imaging for DPDT applications. Image reproducibility (I.R.) and image interference (I.I.) analysis were performed. The results showed that the I.R. value of this fluorescence diagnostic system was higher than 99.0%, and the I.I. from external light sources was lower than 3.0%. In addition, the result of an in vivo study showed that the Chlorin e6 red fluorescence and the scope of distribution of B16-F10 melanoma cells in a mouse ears vein could be measured clearly using our device; however, the comparison studio with 395-nm LED lights could not focus or capture the red fluorescence effectively.

Rapid ranging through evaluation of image distortion.

Distortion is an undesirable aberration found in optical imaging systems, necessitating numerical calibration. However, the fact that image distortion changes with observation distance can be used for ranging. This study developed a rapid, passive-ranging technique, which is simple, incurs low costs, results in minimal interference, and requires few parameters. After determining the location of reference points, the relationship between the normalized mean distortion of images and observation distance is described using two mathematical models, one of which is based on distortion theory and the other is derived from the curve fitting of the experimental results. Analyzing the instantaneous rate of image distortion can also assist in ranging. The proposed technique demonstrates high sensitivity at closer observation distances, but loses effectiveness as observation distances increase.

A filter lens for optical compensation in transmission spectrum

The absorbing filter [1] is an optical element employed for isolating regions of a spectrum. In general, the thicker the absorbing filter material, the more wavelengths it will absorb. However, most optical filter products ignore light diffusion and are made with a constant thickness. While the non-collimated beams pass through the filter, the optical paths vary with incident angles. Thus, the absorption difference happens and leads to the poor uniformity of transmission spectrum. In our work, a filter lens was developed to achieve the similar function of interference filter and ND filter with better spectrum uniformity. It is mounted onto a designed macro lens and supplies it with a good spectrum aberration correction. The shape of the filter lens is designed to eliminate the optical path differences between the light beams in the medium. The macro lens is made of neutral glass and shaped into symmetrical biconvex for achieving macro imaging. The spectrum characteristic of the filter lens depends on the material of the absorbing filter. In the experiment, the filter lens was prepared. The experimental results show that the spectrum uniformity of the filter lens is better than that of the normal filter.

The Non-linear Logarithm Method (NLLM) to adjust the color deviation of fluorescent images

Fluorescence objects can be excited by ultraviolet (UV) light and emit a specific light of longer wavelength in biomedical experiments. However, UV light causes a deviation in the blue violet color of fluorescent images. Therefore, this study presents a color deviation adjustment method to recover the color of fluorescent image to the hue observed under normal white light, while retaining the UV light-excited fluorescent area in the reconstructed image. Based on the Gray World Method, we proposed a non-linear logarithm method (NLLM) to restore the color deviation of fluorescent images by using a yellow filter attached to the front of a digital camera lens in the experiment. Subsequently, the luminance datum of objects can be divided into the red, green, and blue (R/G/B) components which can determine the appropriate intensity of chromatic colors. In general, the datum of fluorescent images transformed into the CIE 1931 color space can be used to evaluate the quality of reconstructed images by the distribution of x-y coordinates. From the experiment, the proposed method NLLM can recover more than 90% color deviation and the reconstructed images can approach to the real color of fluorescent object illuminated by white light.