Soongho Park

An All-Fiber-Optic Combined System of Noncontact Photoacoustic Tomography and Optical Coherence Tomography

We propose an all-fiber-based dual-modal imaging system that combines noncontact photoacoustic tomography (PAT) and optical coherence tomography (OCT). The PAT remotely measures photoacoustic (PA) signals with a 1550-nm laser on the surface of a sample by utilizing a fiber interferometer as an ultrasound detector. The fiber-based OCT, employing a swept-source laser centered at 1310 nm, shares the sample arm of the PAT system. The fiber-optic probe for the combined system was homemade with a lensed single-mode fiber (SMF) and a large-core multimode fiber (MMF). The compact and robust common probe is capable of obtaining both the PA and the OCT signals at the same position without any physical contact. Additionally, the MMF of the probe delivers the short pulses of a Nd:YAG laser to efficiently excite the PA signals. We experimentally demonstrate the feasibility of the proposed dual-modal system with a phantom made of a fishing line and a black polyethylene terephthalate fiber in a tissue mimicking solution. The all-fiber-optic system, capable of providing complementary information about absorption and scattering, has a promising potential in minimally invasive and endoscopic imaging.

Photoacoustic signal measurement using thin film Fabry-Perot optical interferometer for photoacoustic microscopy

A photoacoustic signal measurement system using Fabry-Perot optical interferometer (FPI) for microscopy is presented. Most of the photoacoustic imaging systems have limitation by opaque ultrasound transducer in the alignment system setup. Thus, the excitation laser source should avoid the transducer to illuminate a sample, which makes the system difficult to build-up. To solve this difficulty, a FPI based on Polydimethylsiloxane (PDMS) thin film has been implemented and applied to measure the acoustic wave signal in this work. A tunable laser was used for choosing the Q-point at which the signal has the highest and/or linear response to the signal generated from the sample. When the acoustic wave arrives the PDMS film surface, its thickness is modulated, which affect the FPI interference signal and allows to have noncontact measurement of the photoacoustic signal.

Noncontact measurement of elasticity using optical fiber-based heterodyne interferometer and laser ultrasonics

We propose the noncontact measurement of elasticity by using an optical fiber heterodyne interferometer and laser ultrasonics. The surface acoustic wave (SAW), that is generated by the laser pulse irradiation on the sample surface and propagating along the surface, is optically monitored by the heterodyne interferometer without taking any contact with the sample. By taking several measurements with changing the relative distance between the excitation and the measurement points, the phase velocity of SAW was calculated and from which the elasticity of the sample could be obtained. This proposed method was experimentally evaluated by using PDMS samples having various mixing ratio of curing agent and PDMS. For the sample of a 12:1 mixing ratio, the phase velocity was measured as about 39.46 m/s and the Youngs modulus as about 1987 kPa. This technique is expected to detect the mechanical properties of biological tissues also.

Coherent anti-Stokes Raman scattering microscopy based on polarization maintaining photonics crystal fiber

We present the coherent anti-Stokes Raman scattering (CARS) microscopy system that has been implemented by using a photonic crystal polarization maintaining optical fiber. Free space CARS system is hard in alignment and unstable in harsh environment. To overcome this problem the femto-second laser pulses of pump and the Stokes beams were delivered through the optical fiber, so that the system became less complex and robust to the surrounding environment. In order to confirm the feasibility of the fiber-based CARS system, the CARS images of polystyrene beads and zinc oxide (ZnO) are presented.

All optical fiber combined-imaging system of photoacoustic and optical coherence tomography

We present an all optical fiber combined-imaging system that integrates non-contact photoacoustic tomography (NPAT) and optical coherence tomography (OCT) to simultaneously provide PA and OCT images. The fiber-based PAT system utilizing a Mach-Zehnder interferometer with a fiber laser of 1550 nm measures the photoacoustic signal at the sample surface. For the generation of a PA signal, a pulse train from a bulk type Nd:YAG laser illuminates the sample via a large core multimode optical fiber. The fiber-based OCT operating at a center wavelength of 1310 nm allowed is combined with the fiber-based PAT system by sharing the same optical fiber probe. The two lights from the fiber laser and the OCT source are guided into the probe through each port of a 2 by 2 optical fiber coupler. The back-reflected lights from the sample are guided to respective imaging systems by the same coupler. With these both NPAT and OCT images could be co-registered without physical contact with the sample. To demonstrate the feasibility of the proposed system, a phantom experiment has been carried out with a phantom composed of a black PET fiber and a fishing wire. The proposed all fiber-optic combined-imaging system has the potential for minimally invasive and improved diagnosis.

Photoacoustic microscopy based on polydimethylsiloxane thin film Fabry-Perot optical interferometer

We present a photoacoustic microscopy (PAM) system based on a Fabry-Perot Interferometer (FPI) consisting of a transparent Polydimethylsiloxane (PDMS) thin film. Most of the PAM systems have limitations with the system alignment because the ultrasound transducers for detection are not transparent. Therefore, the excitation laser source should avoid the opaque transducer to illuminate the sample, which makes the system difficult to build-up. Especially, the system volume is highly limited to be compact. In our experiment, to solve these difficulties, a FPI based on the PDMS film has been implemented and applied to measure the acoustic wave signal. The system uses a FPI as an acoustic wave detector instead of a conventional ultrasound transducer. A tunable laser was used to choose the quadrature-point at which the signal has the highly sensitve and linear response to the acoustic wave. Also a 20Hz pulsed Nd:YAG laser was used to generate acoustic waves from a sample. When the acoustic waves arrive at the PDMS film, one of the surfaces of the film is modulated at the detecting point, which gives the tuned FPI interference signal. From the signal arriving time, the depth location of the sample is calculated. As a primary experiment using the PDMS thin film as an ultrasound transducer, a couple of narrow black friction tapes located in a water container were used as the samples. This proposed imaging method can be used in various applications for the detection and measurement of acoustic waves.

Photoacoustic Microscopy Equipped with a Lensed Fiber For Pulsed Diode Laser Scanning

We present a photoacoustic microscopy using a self-built lensed fiber to guide the excitation laser. A pulsed laser diode was used to generate the acoustic signal, and the laser beam was focused on the sample.

Fiber-based dual modal system for noncontact photoacoustic and optical coherence tomography

We present a dual modal system combining noncontact photoacoustic tomography and optical coherence tomography. The proposed system, composed of fiber-optic networks, uses one probing beam path, which provides the noncontact measurements. Multimodal images of phantoms were acquired to demonstrate the capability of the proposed system.

Dual modality of non-contact photoacoustic tomography and fluorescence imaging using double cladding fiber

We present a fiber-based dual-modal imaging system that combines non-contact photoacoustic tomography (NCPAT) and fluorescence imaging by using double cladding fiber (DCF). The NCPAT system utilizing an all-fiber heterodyne interferometer as an ultrasound detector measures the photoacoustic signal at the sample surface without physical contact. Fluorescence imaging system is composed of fiber-optics to deliver the excitation light and the emission light. For combined system the probe consists of a specially fabricated DCF coupler and a lensed fiber so that we can simultaneously acquire the signals of two systems with the same probe. The DCF has a core and two claddings, inner and outer, which allows two concentric light-guiding channels via the core and the inner cladding. The lensed fiber of the DCF probe is compactly fabricated to focus the interferometer light and the excitation light, and to efficiently collect the fluorescence signal. To demonstrate the feasibility of the proposed dual-modal system, we have conducted phantom experiments using tissue mimicking phantoms which contained a couple of tubes filled with fluorescein solution and black ink, respectively. The proposed imaging system is implanted with fiber-optic configurations so that it has the potential for minimally invasive and improved diagnosis and guided treatment of diseases.

Spin90 deficiency increases CXCL13-mediated B cell migration.

SPIN90 regulates actin dynamics, which is important for cell migration control. CXCL13‐mediated B cell migration is essential for B cell immune responses. In this study, we investigated the role of SPIN90 in CXCL13‐mediated B cell migration using Spin90 gene‐deficient mice. Our chemokinesis analysis and transwell cell migration assay showed that SPIN90 is involved in CXCL13‐mediated B cell migration. Moreover, the level of CXCR5, which is CXCL13 receptor, was increased in SPIN90‐deficient B cells compared with wild‐type B cells. Overall, our data suggest that SPIN90 plays an important role in B cell immune responses through the regulation of CXCL13‐mediated B cell migration.