Cheol Song

Forward imaging OCT endoscopic catheter based on MEMS lens scanning

This Letter reports a fully packaged microelectromechanical system (MEMS) endoscopic catheter for forward imaging optical coherence tomography (OCT). Two-dimensional optical scanning of Lissajous patterns was realized by the orthogonal movement of two commercial aspherical glass lenses laterally mounted on two resonating electrostatic MEMS microstages at low operating voltages. The MEMS lens scanner was integrated on a printed circuit board and packaged with an aluminum housing, a gradient index fiber collimator, and an objective lens. A home-built spectral-domain OCT system with 60 kHz A-line acquisition rate was combined with the endoscopic MEMS catheter. Three-dimensional images of 256×256×995 voxels were directly reconstructed by mapping the A-line datasets along the Lissajous patterns. The endoscopic catheter can provide a new direction for forward endoscopic OCT imaging.

Fiber-optic OCT sensor guided “SMART” micro-forceps for microsurgery

A handheld Smart Micromanipulation Aided Robotic-surgery Tool (SMART) micro-forceps guided by a fiber-optic common-path optical coherence tomography (CP-OCT) sensor is presented. A fiber-optic CP-OCT distance and motion sensor is integrated into the shaft of a micro-forceps. The tool tip position is manipulated longitudinally through a closed loop control using a piezoelectric motor. This novel forceps design could significantly enhance safety, efficiency and surgical outcomes. The basic grasping and peeling functions of the micro-forceps are evaluated in dry phantoms and in a biological tissue model. As compared to freehand use, targeted grasping and peeling performance assisted by active tremor compensation, significantly improves micro-forceps user performance.

Micromachined lens microstages for two-dimensional forward optical scanning

This work presents a novel approach for a miniaturized optical scanning module based on lateral and piston motion of two commercial lenses by MEMS actuation. Two aspheric glass lenses of 1 mm diameter are assembled on two electrostatically actuated microstages moving along perpendicular axes to tilt optical path. The compact integration secures the effective beam aperture of 0.6 mm within the device width of 2 mm. The lens mass provides high-Q motions at low operating voltages of DC 5 V and AC 10 V, i.e., the lateral angle of 4.6 degrees at 277 Hz and the vertical angle of 5.3 degrees at 204 Hz. The device can provide a new direction for miniaturizing laser scanning based endoscopes or handheld projectors.

Simultaneous blood flow and blood oxygenation measurements using a combination of diffuse speckle contrast analysis and near-infrared spectroscopy

Abstract. A combined diffuse speckle contrast analysis (DSCA)–near-infrared spectroscopy (NIRS) system is proposed to simultaneously measure qualitative blood flow and blood oxygenation changes in human tissue. The system employs an optical switch to alternate two laser sources at two different wavelengths and a CCD camera to capture the speckle image. Therefore, an optical density can be measured from two wavelengths for NIRS measurements and a speckle contrast can be calculated for DSCA measurements. In order to validate the system, a flow phantom test and an arm occlusion protocol for arterial and venous occlusion were performed. Shorter exposure times (<1  ms) show a higher drop (between 50% and 66%) and recovery of 1/KS2 values after occlusion (approximately 150%), but longer exposure time (3 ms) shows more consistent hemodynamic changes. For four subjects, the 1/KS2 values dropped to an average of 82.1±4.0% during the occlusion period and the average recovery of 1/KS2 values after occlusion was 109.1±0.8%. There was also an approximately equivalent amplitude change in oxyhemoglobin (OHb) and deoxyhemoglobin (RHb) during arterial occlusion (max RHb=0.0085±0.0024  mM/DPF, min OHb=−0.0057±0.0044  mM/DPF). The sensitivity of the system makes it a suitable modality to observe qualitative hemodynamic trends during induced physiological changes.

Two-step synthesis of agglomeration-free peroxidase-like Co3O4 nanoparticles–carbon nitride nanotube hybrids enabling a high redox activity

We report a two-step synthesis method to fabricate peroxidase-like Co3O4 nanoparticles–carbon nitride nanotube (Co3O4 NPs–CNNT) hybrid catalysts enabling a high redox activity. At first, the energy-dispersive spectrometer mapping shows that the CNNT surface is wrapped by the Co(OH)2 after the first solvothermal step using cobalt acetylacetonate of Co(acac)3 precursor and triethylene glycol solvent. Also, the X-ray diffraction and photoelectron spectroscopy measurements support that the subsequent heat treatment transforms the Co(OH)2 into the crystalline Co3O4 NPs on the CNNT. Also, the near-edge X-ray absorption fine structure analysis and density functional theory calculations provide a clue regarding the role of pyridine- and graphite-like N atoms of the CNNT to anchor agglomeration-free Co3O4 NPs on its surface. Indeed, the Co3O4 NPs–CNNT hybrid shows high peroxidase-like redox activity for 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2. Furthermore, the electron spinning resonance analysis elucidates the mechanism for the high peroxidase-like redox activity, where the electrons of Co3O4 NPs and a CNNT first move to H2O2 and then H2O2 form one OH radicals and one OH ion. Next, TMB is oxidized by a Co3O4 NPs–CNNT hybrid and generates electrons. Then, the generated electrons offset to maintain the neutral state of a Co3O4 NPs–CNNT hybrid. The XRD data of a Co3O4 NPs–CNNT hybrid after the peroxidase reaction further supports our proposed model.

Avian embryo monitoring during incubation using multi-channel diffuse speckle contrast analysis

Determining the survival rate of avian embryos during incubation is essential for cost-saving in the poultry industry. A multi-channel diffuse speckle contrast analysis (DSCA) system, comprising four optical fiber channels, is proposed to achieve noninvasive in vivo measurements of deep tissue flow. The system was able to monitor chick embryo vital signs over the entire incubation period. Moreover, it proved useful in distinguishing between chick embryos in healthy and weakened conditions.

Polarization-sensitive spectral-domain optical coherence tomography using a multi-line single camera spectrometer

We describe a polarization sensitive spectral domain optical coherence tomography technique based on a single camera spectrometer that includes a multiplexed custom grating, camera lenses, and a high-speed three-line CCD camera. Two orthogonally polarized beams could be separately taken by two lines of the camera as a result of vertically different incident angles. The system could provide the imaging capabilities of a full camera speed and increased measurable depth. The proposed optical coherence tomography system could make a distinction between the normal muscle and cancerous tissue from the chest of a DSred GFP mouse and the OCT images were compared with those of in vivo confocal microscopy.

SMART micro-scissors based precise incision

Hand tremor reduction is important to achieve stable micro manipulation of the tool tip. A micro-scissors can be used for cutting delicate tissues safely. Here, we implement an OCT distance sensor guided SMART micro-scissors which could incise micro-surgical targets precisely and horizontally. Compared to freehand incision, it demonstrates enhanced incision performance on dry phantoms with great tremor suppression.

Development and preliminary results of bimanual smart micro-surgical system using a ball-lens coupled OCT distance sensor.

Bimanual surgery enhances surgical effectiveness and is required to successfully accomplish complex microsurgical tasks. The essential advantage is the ability to simultaneously grasp tissue with one hand to provide counter traction or exposure, while dissecting with the other. Towards enhancing the precision and safety of bimanual microsurgery we present a bimanual SMART micro-surgical system for a preliminary ex-vivo study. To the best of our knowledge, this is the first demonstration of a handheld bimanual microsurgical system. The essential components include a ball-lens coupled common-path swept source optical coherence tomography sensor. This system effectively suppresses asynchronous hand tremor using two PZT motors in feedback control loop and efficiently assists ambidextrous tasks. It allows precise bimanual dissection of biological tissues with a reduction in operating time as compared to the same tasks performed with conventional one-handed approaches.

Fabrication of size-controlled Co nanoparticles via mediation of H-adatoms on pyridine-like nitrogen of carbon nitride nanotubes and their superior catalytic performance for hydrogen generation

We report a new route to fabricate size-controlled Co nanoparticles (NPs) on carbon nitride nanotubes (CNNTs). The size of the Co nanoparticles is controlled down to 2 nm. Our density functional theory calculations provide the clue for the formation mechanism of these size-controllable Co NPs in the presence of sodium hypophosphite, water, Co2+ ions and OH− ions on the pyridine-like nitrogen of CNNTs. First, two H-adatoms from water are bonded onto the pyridine-like nitrogen while sodium hypophosphite is bonded with the oxygen of water. Next, the reduction of Co2+ ions occurs via combination with two electrons donated from these two H-adatoms. The Co NPs-CNNT fabricated via this method shows the highest hydrogen generation rate of 19.6 kg h−1 per kg of catalyst from aqueous metal hydride solution. This superior catalytic activity (about 82 times higher than that for the Co powder in the bulk state) is attributed to the increased surface area, as well as the approx. 1.5 times larger number of Co nanoparticle catalysts with about 2 nm sizes formed via mediation of the two H-adatoms bonded to the pyridine-like nitrogen.