Harmonic Imaging of Stem Cells in Whole Blood at GHz Pixel Rate.

The pre-clinical validation of cell therapies requires monitoring the biodistribution of transplanted cells in tissues of host organisms. Real-time detection of these cells in the circulatory system and identification of their aggregation state is a crucial piece of information, but necessitates deep penetration and fast imaging with high selectivity, subcellular resolution, and high throughput. In this study, multiphoton-based in-flow detection of human stem cells in whole, unfiltered blood is demonstrated in a microfluidic channel. The approach relies on a multiphoton microscope with diffractive scanning in the direction perpendicular to the flow via a rapidly wavelength-swept laser. Stem cells are labeled with metal oxide harmonic nanoparticles. Thanks to their strong and quasi-instantaneous second harmonic generation (SHG), an imaging rate in excess of 10 000 frames per second is achieved with pixel dwell times of 1 ns, a duration shorter than typical fluorescence lifetimes yet compatible with SHG. Through automated cell identification and segmentation, morphological features of each individual detected event are extracted and cell aggregates are distinguished from isolated cells. This combination of high-speed multiphoton microscopy and high-sensitivity SHG nanoparticle labeling in turbid media promises the detection of rare cells in the bloodstream for assessing novel cell-based therapies.

Pulsed swept-source FDML-MOPA laser with kilowatt picosecond pulses around 1550†nm.

Swept-source lasers are versatile light sources for spectroscopy, imaging, and microscopy. Swept-source-powered multiphoton microscopy can achieve high-speed, inertia-free point scanning with MHz line-scan rates. The recently introduced spectro-temporal laser imaging by diffractive excitation (SLIDE) technique employs swept-source lasers to achieve kilohertz imaging rates by using a swept-source laser in combination with a diffraction grating for point scanning. Multiphoton microscopy at a longer wavelength, especially in the shortwave infrared (SWIR) region, can have advantages in deep tissue penetration or applications in light detection and ranging (LiDAR). Here we present a swept-source laser around 1550 nm providing high-speed wavelength agility and high peak power pulses for nonlinear excitation. The swept-source laser is a Fourier-domain mode-locked (FDML) laser operating at 326 kHz sweep rate. For high peak powers, the continuous wave (cw) output is pulse modulated to short picosecond pulses and amplified using erbium-doped fiber amplifiers (EDFAs) to peak powers of several kilowatts. This FDML-master oscillator power amplifier (FDML-MOPA) setup uses reliable, low-cost fiber components. As proof-of-principle measurement, we show third-harmonic generation (THG) using harmonic nanoparticles at the 10 MHz pulse excitation rate. This new, to the best of our knowledge, laser source provides unique performance parameters for applications in nonlinear microscopy, spectroscopy, and ranging.

Measuring Subnational Trade Competitiveness.

Much research has tried to measure the competitiveness of territorial units such as countries and subnational regions. We propose new measures of subnational trade competitiveness that reflect the economic focus of regions on their country's comparative advantage. Our approach starts with data on the revealed comparative advantage of countries at the industry level. We then combine these measures with data on the employment structure of subnational regions to arrive at measures of subnational trade competitiveness. In total, we offer data for 6,475 regions across 63 countries and over a time period of 21 years. In this article, we introduce our measures and provide descriptive evidence, include two case studies for Bolivia and South Korea, that shows the plausibility of these measures. These data are relevant for many areas of research, including on the competitiveness of territorial units, the economic and political impact of trade on importing countries, and the economic and political consequences of globalization.

Extended coherence length Fourier domain mode locked lasers at 1310 nm.

Fourier domain mode locked (FDML) lasers are excellent tunable laser sources for frequency domain optical coherence tomography (FD-OCT) systems due to their combination of high sweep rates, large tuning ranges, and high output powers. However, conventional FDML lasers provide coherence lengths of only 4-10 mm, limiting their use in demanding applications such as intravascular OCT where coherence lengths of >20 mm are required for optimal imaging of large blood vessels. Furthermore, like most swept lasers, conventional FDML lasers produce only one useable sweep direction per tunable filter drive cycle, halving the effective sweep rate of the laser compared to the filter drive frequency. Here, we demonstrate a new class of FDML laser incorporating broadband dispersion compensation near 1310 nm. Elimination of chromatic dispersion in the FDML cavity results in the generation of forward (short to long wavelength) and backward (long to short wavelength) sweeps with substantially identical properties and coherence lengths of >21 mm. This advance enables long-range, high-speed FD-OCT imaging without the need for optical buffering stages, significantly reducing laser cost and complexity.

In-vitro and in-vivo imaging of coronary artery stents with Heartbeat OCT.

To quantify the impact of cardiac motion on stent length measurements with Optical Coherence Tomography (OCT) and to demonstrate in vivo OCT imaging of implanted stents, without motion artefacts. The study consists of: clinical data evaluation, simulations and in vivo tests. A comparison between OCT-measured and nominal stent lengths in 101 clinically acquired pullbacks was carried out, followed by a simulation of the effect of cardiac motion on stent length measurements, experimentally and computationally. Both a commercial system and a custom OCT, capable of completing a pullback between two consecutive ventricular contractions, were employed. A 13 mm long stent was implanted in the left anterior descending branch of two atherosclerotic swine and imaged with both OCT systems. The analysis of the clinical OCT images yielded an average difference of 1.1 ± 1.6 mm, with a maximum difference of 7.8 mm and the simulations replicated the statistics observed in clinical data. Imaging with the custom OCT, yielded an RMS error of 0.14 mm at 60 BPM with the start of the acquisition synchronized to the cardiac cycle. In vivo imaging with conventional OCT yielded a deviation of 1.2 mm, relative to the length measured on ex-vivo micro-CT, while the length measured in the pullback acquired by the custom OCT differed by 0.20 mm. We demonstrated motion artefact-free OCT-imaging of implanted stents, using ECG triggering and a rapid pullback.

High-resolution optical coherence tomography imaging of the living kidney.

Optical coherence tomography (OCT) is a rapidly emerging imaging modality that can provide non-invasive, cross-sectional, high-resolution images of tissue morphology in situ and in real-time. In the present series of studies, we used a high-speed OCT imaging system equipped with a frequency-swept laser light source (1.3 mum wavelength) to study living kidneys in situ. Adult, male Munich-Wistar rats were anesthetized, a laparotomy was performed and the living kidneys were exposed for in situ observation. We observed the kidneys prior to, during and following exposure to renal ischemia induced by clamping the renal artery. The effects of intravenous mannitol infusion (1.0 ml of 25%) prior to and during renal ischemia were also studied. Finally, living kidneys were flushed with a renal preservation solution, excised and observed while being stored at 0-4 degrees C. Three-dimensional OCT data sets enabled visualization of the morphology of the uriniferous tubules and the renal corpuscles. When renal ischemia was induced, OCT revealed dramatic shrinkage of tubular lumens due to swelling of the lining epithelium. Three-dimensional visualization and volumetric rendering software provided an accurate evaluation of volumetric changes in tubular lumens in response to renal ischemia. Observations of kidneys flushed with a renal preservation solution and stored at 0-4 degrees C also revealed progressive and significant loss of tubular integrity over time. Intravenous infusion of mannitol solution resulted in thinning of the tubular walls and an increase in the tubular lumen diameters. Mannitol infusion also prevented the cell swelling that otherwise resulted in shrinkage of proximal tubule lumens during ischemia. We conclude that OCT represents an exciting new approach to visualize, in real-time, pathological changes in the living kidney in a non-invasive fashion. Possible clinical applications are discussed.

Swept source optical coherence microscopy using a Fourier domain mode-locked laser.

Swept source optical coherence microscopy (OCM) enables cellular resolution en face imaging as well as integration with optical coherence tomography (OCT) cross sectional imaging. A buffered Fourier domain mode-locked (FDML) laser light source provides high speed, three dimensional imaging. Image resolutions of 1.6 microm x 8 microm (transverse x axial) with a 220 microm x 220 microm field of view and sensitivity higher than 98 dB are achieved. Three dimensional cellular imaging is demonstrated in vivo in the Xenopus laevis tadpole and ex vivo in the rat kidney and human colon.