Kyungjin Park

Fast optical-resolution photoacoustic microscopy using a 2-axis water-proofing MEMS scanner

Optical-resolution photoacoustic microscopy (OR-PAM) is a novel label-free microscopic imaging tool to provide in vivo optical absorbing contrasts. Specially, it is crucial to equip a real-time imaging capability without sacrificing high signal-to-noise ratios (SNRs) for identifying and tracking specific diseases in OR-PAM. Herein we demonstrate a 2-axis water-proofing MEMS scanner made of flexible PDMS. This flexible scanner results in a wide scanning range (9 × 4 mm2 in a transverse plane) and a fast imaging speed (5 B-scan images per second). Further, the MEMS scanner is fabricated in a compact footprint with a size of 15 × 15 × 15 mm3. More importantly, the scanning ability in water makes the MEMS scanner possible to confocally and simultaneously reflect both ultrasound and laser, and consequently we can maintain high SNRs. The lateral and axial resolutions of the OR-PAM system are 3.6 and 27.7 μm, respectively. We have successfully monitored the flow of carbon particles in vitro with a volumetric display frame rate of 0.14 Hz. Finally, we have successfully obtained in vivo PA images of microvasculatures in a mouse ear. It is expected that our compact and fast OR-PAM system can be significantly useful in both preclinical and clinical applications.

ISAR Imaging of Multiple Targets Using Edge Detection and Hough Transform

This paper describes a fast method to derive ISAR images of multiple targets with different motion parameters. We use image processing techniques, edge detection and the Hough transform to find the slope of the range profile history of each target and to separate each range profile history. Simulation results of two closely spaced targets with different motion parameters confirm the effectiveness of this method.

Efficient RCS Prediction Method Using Angular Division Algorithm

We propose an efficient algorithm to calculate the radar cross section of electrically large and complex targets using a shooting and bouncing rays method. The proposed method, which is based on an angular division algorithm, reduces the number of initial rays and operations for each intersection test, and accelerates the ray tracing without loss of accuracy. Numerical results show the accuracy and efficiency of the proposed method.

Construction of Training Database Based on High Frequency RCS Prediction Methods For ATR

Due to the difficulty of creating training databases using all real enemy targets, it is necessary to derive them using computer simulations. In this paper, we apply three high frequency radar cross section (RCS) methods to create a training database for automatic target recognition (ATR) using 1-D range profiles. These methods are: physical optics (PO), physical theory of diffraction (PTD) and shooting and bouncing ray (SBR). Experimental results derived from the performance of combinational feature space trajectory with a new distance metric (FSTND) classifier show that PO+PTD is the most efficient method for ATR because of the additional information by diffraction terms. SBR shows poor performance due to the cavity structure.

High-speed and high-SNR photoacoustic microscopy based on a galvanometer mirror in non-conducting liquid

Optical-resolution photoacoustic microscopy (OR-PAM), a promising microscopic imaging technique with high ultrasound resolution and superior optical sensitivity, can provide anatomical, functional, and molecular information at scales ranging from the microvasculature to single red blood cells. In particular, real-time OR-PAM imaging with a high signal-to-noise ratio (SNR) is a prerequisite for widespread use in preclinical and clinical applications. Although several technical approaches have been pursued to simultaneously improve the imaging speed and SNR of OR-PAM, they are bulky, complex, not sensitive, and/or not actually real-time. In this paper, we demonstrate a simple and novel OR-PAM technique which is based on a typical galvanometer immersed in non-conducting liquid. Using an opto-ultrasound combiner, this OR-PAM system achieves a high SNR and fast imaging speed. It takes only 2 seconds to acquire a volumetric image with a wide field of view (FOV) of 4 × 8 mm2 along the X and Y axes, respectively. The measured lateral and axial resolutions are 6.0 and 37.7 μm, respectively. Finally, as a demonstration of the system’s capability, we successfully imaged the microvasculature in a mouse ear in vivo. Our new method will contribute substantially to the popularization and commercialization of OR-PAM in various preclinical and clinical applications.

A PDMS-Based 2-Axis Waterproof Scanner for Photoacoustic Microscopy.

Optical-resolution photoacoustic microscopy (OR-PAM) is an imaging tool to provide in vivo optically sensitive images in biomedical research. To achieve a small size, fast imaging speed, wide scan range, and high signal-to-noise ratios (SNRs) in a water environment, we introduce a polydimethylsiloxane (PDMS)-based 2-axis scanner for a flexible and waterproof structure. The design, theoretical background, fabrication process and performance of the scanner are explained in details. The designed and fabricated scanner has dimensions of 15 × 15 × 15 mm along the X, Y and Z axes, respectively. The characteristics of the scanner are tested under DC and AC conditions. By pairing with electromagnetic forces, the maximum scanning angles in air and water are 18° and 13° along the X and Y axes, respectively. The measured resonance frequencies in air and water are 60 and 45 Hz along the X axis and 45 and 30 Hz along the Y axis, respectively. Finally, OR-PAM with high SNRs is demonstrated using the fabricated scanner, and the PA images of micro-patterned samples and microvasculatures of a mouse ear are successfully obtained with high-resolution and wide-field of view. OR-PAM equipped with the 2-axis PDMS based waterproof scanner has lateral and axial resolutions of 3.6 μm and 26 μm, respectively. This compact OR-PAM system could potentially and widely be used in preclinical and clinical applications.

Handheld Photoacoustic Microscopy Probe

Optical resolution photoacoustic microscopy (OR-PAM) is a non-invasive, label-free method of in vivo imaging with microscopic resolution and high optical contrast. Based on intrinsic contrasts, OR-PAM has expanded to include in vivo vessel imaging, flow cytometry, physiological parameter analysis, and single-cell characterization. However, since conventional OR-PAM systems have a fixed tabletop configuration, a large system size, and slow imaging speed, their use in preclinical and clinical studies remains limited. In this study, using microelectromechanical systems (MEMS) technology, we developed a handheld PAM probe with a high signal-to-noise ratio and image rate. To enable broader application of the OR-PAM system, we reduced its size and combined its fast scanning capabilities into a small handheld probe that uses a 2-axis waterproof MEMS scanner (2A-WP-MEMS scanner). All acoustical, optical, and mechanical components are integrated into a single probe with a diameter of 17 mm and a weight of 162 g. This study shows phantom and in vivo images of various samples acquired with the probe, including carbon fibers, electrospun microfibers, and the ear, iris, and brain of a living mouse. In particular, this study investigated the possibility of clinical applications for melanoma diagnosis by imaging the boundaries and morphology of a human mole.

Development of a photoacoustic handheld probe using 2-axis MEMS scanner

Optical resolution photoacoustic tomography (OR-PAM) is a non-invasive imaging method that uses endogenous contrast agents in the body, such as hemoglobin in the blood. OR-PAM has a resolution equivalent to a microscope, and has high optical contrast. OR-PAM has been made to expand the application to the medical field by increasing the speed of imaging and minimizing the size of the system. In this research, we accomplished these two specifications by using MEMS technology to integrate a fast scan functionality into a handheld probe. Using MEMS technology, beam guides, ultrasound guidance, and mechanical scanning subsystems were integrated into a single small probe. The measured lateral resolution is 16 μm, and the measured B-scan and volume imaging rate are 35 and 0.2 Hz to obtain a photoacoustic (PA) image with 200 and 700 pixels. We imaged a variety of phantom and in vivo samples such as carbon fibers, mouse ears, eyes, and brains.

Fabrication of Polymer Microstructures of Various Angles via Synchrotron X-Ray Lithography Using Simple Dimensional Transformation

In this paper, we developed a method of fabricating polymer microstructures at various angles on a single substrate via synchrotron X-ray lithography coupled with simple dimensional transformations. Earlier efforts to create various three-dimensional (3D) features on flat substrates focused on the exposure technology, material properties, and light sources. A few research groups have sought to create microstructures on curved substrates. We created tilted microstructures of various angles by simply deforming the substrate from 3D to two-dimensional (2D). The microstructural inclination angles changed depending on the angles of the support at particular positions. We used convex, concave, and S-shaped supports to fabricate microstructures with high aspect ratios (1:11) and high inclination angles (to 79°). The method is simple and can be extended to various 3D microstructural applications; for example, the fabrication of microarrays for optical components, and tilted micro/nanochannels for biological applications.

Handheld optical-resolution photoacoustic microscopy probe for preclinical application

In this study, we developed an imaging device for preclinical and clinical application using photoacoustic effect. The photoacoustic effect is to make ultrasound images using light as its name illustrates. Light irradiated in a short time (nano seconds) is absorbed by the tissue, and the local pressure is generated by the thermo-elastic expansion. The photoacoustic effect is a safe method of imaging because it uses an endogenous chromophore in the human body without the use of an external contrast agent. In this study, the image uses an optical-resolution photoacoustic microscope (OR-PAM) which has a resolution of 12 ¥ìm. The conventional or-pam has the disadvantage of being slow and bulky using mechanical motors. To overcome this problem, our research team developed a photoacoustic imaging system that uses a MEMS scanner to equip a fast image capability into a compact handheld probe.