Exploring a photo-acousto-optic effect for noncontacting photoacoustic sensing.

To avoid the use of ultrasound transducers and coupling gel in photoacoustic microscopy (PAM), we propose photo-acousto-optic tomography (PAOT) for noncontact photoacoustic (PA) sensing. The process consists of two parts. The first portion is the same as typical PAM, which employs a pulsed laser to induce acoustic waves. The difference from typical methods lies in the second part of the process, which applies a DC beam, rather than a conventional transducer, to sense the PA signal. A two-beam optical microscope system was designed to verify the PAOT effect, whereby an AC spot acted as the source to induce a PA signal, while a DC beam is applied to induce the acousto-optic effect for detection of the acoustic wave. We demonstrated the preliminary result that 5-100 Hz AC radiation could derive PA waves in a water-like medium along with detection sensitivity as high as 4.9%-10.0%; besides, the signal waveform could be detected by a DC spot 10-100 µm away for noncontact sensing with detection sensitivity of about 3.7%-10.4%. Without the need for a transducer or coupling gel, PAOT has the potential to modify conventional PAM into a pure optical system, which could make PA imaging more promising in practical applications.

Applying RGB LED in full-field optical coherence tomography for real-time full-color tissue imaging.

A conventional handheld skin camera is suitable for 2D inspection of shallow skin. Due to its high resolution and noninvasiveness, optical coherence tomography (OCT) has become a popular medical-imaging technology. Among OCT schemes, full-field optical coherence tomography (FF-OCT) is suitable for rapid en face imaging, as it uses a 2D imaging device for pixel processing of a sample plane. Because of its wide bandwidth and long lifetime, an RGB LED was chosen in an FF-OCT system among three source candidates in this study. A full-color tissue image and real-time video were obtained from the system to demonstrate the potential of the RGB LED FF-OCT system in medical imaging. All devices used here can be integrated by micro-optoelectromechanical technology into a handheld model. Noninvasive, real-time, full-color handheld imaging capability contributes to advance dermatology and cosmetology.

[Noninvasive medical imaging system for tissue classification using RGB LED and micro-spectroscopy].

As skin is the exterior organ of human body, cosmetic industry advances year by year. To reveal the details of skin tissue, threedimensional medical imaging is required. Based on the idea of "readout instead of write", a new scheme named spectral classification imaging (SCI) is proposed in the present study to reduce the invasiveness by applying the reflection spectra of the sample points for three-dimensional medical imaging. Broad-band light source and the spectrometer were employed to collect the spectra curves of scanned region, which were classified into several tissue types by their cross-correlations. A colorful tissue tomography can finally be obtained by filling in each image pixel the color indicating the corresponding tissue type. The lateral/longitudinal resolutions and penetration depth were analyzed to characterize the SCI system. The lateral resolution is based on the source's diffraction limit, the longitudinal resolution is by its depth-of-focus, and the penetration depth is equivalent to its skin depth. The imaging results of an amethyst of 0.6 mm (chi-direction) x 0.6 mm (y-direction) with a total of 120 x 120 pixels per frame and a guppy fish of 3.2 mm (chi-direction) x 2.4 mm (y-direction) of 160 x 120 pixels, are presented to show the image quality. The effects of the cross-correlation coefficient and the number of source wavelengths on the imaging results were explored. The value of cross-correlation threshold determines the required time for imaging, the resulted number of tissue groups, and the variety of tissue colors in the imaging result. Owing to its virtual noninvasiveness and easy configuration, the SCI system is highly promising for practical uses. RGB LEDs possess merits of broad bandwidth, low cost, long lifetime, small volume, and are ready to be integrated into a multi-color source module. Replacing the wide-band light source and the spectrometer module with a composite RGB LED with discrete wavelengths and a micro-spectrometer for spectra retrieval, the system has great potential to be minimized as a hand-held product for noninvasive medical imaging. It leads to reduced use of non-eco-friendly cosmetics and extended advance of cosmetic dermatology.

[The study of absorption efficiency and restoring effects of collagen and ascorbic acid on aged skin by fluorescence and reflection spectroscopy].

Collagen is one of the main structural proteins in human dermis. The lack and atrophy of collagen induces the appearance of wrinkles and beginning of aging. L-ascorbic acid has significant effects on skin-whitening and anti-oxidation, which helps keep skin beautiful and healthy, respectively. With auto-fluorescence, the amount of collagen is in proportion to the strength of its fluorescence spectrum. Therefore, a new method is proposed to determine the content of collagen and the health of skin through the analysis of fluorescence and reflection spectra. Compared with conventional chemical analysis, this method needs less time, and is much more noninvasive. Solutions of different concentration of external collagen and L-ascorbic acid were applied on healthy, spotted and wrinkled skin in this study. By the time dependence of fluorescence and reflection spectra, the effects of skin absorption and restoration of collagen and L-ascorbic acid were derived, respectively. The experiment shows that the collagen or L-ascorbic acid solution of adequate concentration is best for skin absorption. Admixed with suitable concentration of L-ascorbic acid, the collagen solution was well absorbed and results in effect of smoothing wrinkles; the effect of L-ascorbic acid to clear up the spots was also demonstrated. By scientific explorations shown above, the restoration effects of cosmetic materials were validated, and people's confusion and myth about skincare products were avoided. Consequently, this study helps advance cosmetic industry.

[Design and application of noninvasive tissue recognition imaging in tomography of human skin and crystal structure].

Cosmetic industry grows fast in recent years. To reveal the image of dermal structure, it is necessary to apply three-dimensional medical imaging technology. To reduce the invasiveness of laser source on tissues, tissue recognition imaging is proposed to retrieve the intrinsic optical property, namely, the reflection spectrum of every scanned point for imaging. The reflection spectra of main kinds of skin tissue, such as melanin, collagen and hemoglobin, were established as reference database. Broad-band rays were then employed to derive the reflection spectrum of each scanned sample element; the tissue type of the scanned point was identified by cross-correlation of the derived spectrum and the database. In imaging program, all scanned points were filled in with their corresponding tissue color, e.g., black for melanin, white for collagen, or red for hemoglobin, and finally the colored skin tomography resulted. Tissue recognition imaging has merits of easy configuration, low cost, color imaging, high resolution and real non-invasiveness. Substituting LED modules for its spectrometer, tissue recognition imaging is promising to be miniaturized as personal and portable skincare devices, which have great potential in future cosmetic market.

The evaluation of interaction between red blood cells in blood coagulation by optical tweezers.

To maintain the life of patients with hemophilia, apoplexy or hemorrhage, appropriate blood coagulation is crucial. To study the microscopic phenomena of blood coagulation and the therapeutic effects of blood medication, optical tweezers were applied to estimate the interaction between red blood cells in the coagulation process. By measuring minimum optical power required to trap the coagulating blood cells, the pN-scale interaction between them can be evaluated. In normal blood sample, the interaction rises in accordance with coagulation time. The addition of heparin attenuates the interaction and postpones the coagulation, whereas the addition of tranexamic acid starts the coagulation early at the beginning and allows the process completed in less time.

Measuring micro-interactions between coagulating red blood cells using optical tweezers.

Agents that alter the dynamics of hemostasis form an important part in management of conditions such as atherosclerosis, cerebrovascular disease, and bleeding diatheses. In this study, we explored the effects of heparin and tranexamic acid on the efficiency of blood coagulation. Using optical tweezers, we evaluated the pN-range micro-interaction between coagulating red blood cells (RBCs) by measuring the minimum power required to trap them. By observing the mobility of RBCs and the intensity of cellular interactions, we found that the coagulation process can be separated into three phases. The effects of heparin and tranexamic acid were examined by observing variations in cellular interaction during the coagulation phases. Heparin attenuated the interaction between RBCs and prolonged the first phase whereas the samples containing tranexamic acid bypassed the first two phases and immediately proceeded to the final one.

Full-color skin imaging using RGB LED and floating lens in optical coherence tomography.

The cosmetic industry has witnessed significant growth in recent years. Conventional hand-held skin cameras allow for 2D inspection of the skin surface. This paper proposes a new model for full-color 3D imaging of the skin tissue using fiber-based optical coherence tomography (OCT). Compared to laser or LD sources, RGB LED was found more suitable and thus chosen in the low-coherence interferometry due to its wider bandwidth. A floating objective lens was used to confocalize the R, G and B imaging planes and to derive a full-color image of the capillary system in the skin tissue. The skin imaging system can be miniaturized to form a new hand-held model using an RGB integrated source, a micro-interferometer module and a high-speed beam steering device. Non-invasive, full-color and hand-held skin imaging contributes to advances in the fields of skin science, dermatology and cosmetology.