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Crossed electrode arrays address some of the challenges associated with 3-D ultrasound imaging because of the significant reduction in the number of elements ( $2{N}$ versus ${N}^{{2}}$ ). However, creating a two-way focused 3-D image in real time is difficult with these arrays because azimuth and elevation dimensions cannot be beamformed at the same time. This work describes a new 3-D imaging technique that uses the flexibility of bias-sensitive substrates to create a high-quality elevation focus on a crossed electrode array. The principle behind this technique is to perform conventional compound imaging with an azimuth set of electrodes while implementing a bias controllable elevation lens with an elevation set of electrodes. On transmit, the biases are chosen to mimic a Fresnel lens. Then, on receive, the Hadamard coding is implemented along the elevation dimension. After decoding, we gain the RF data for each element across the elevation aperture even though there is effectively only one channel in that dimension. A 30-MHz, 128-element crossed electrode relaxor array was fabricated on a 1–3 electrostrictive composite substrate and was used to demonstrate the performance of the imaging technique. The on-axis −6-dB beamwidths were simulated to be 175 and $150~\mu \text{m}$ in the azimuth and elevation directions, respectively, and the focus remained isotropic in the furthest elevation slice. Images were generated of a wire phantom to confirm the performance of the azimuth and elevational radiation patterns with good agreement between simulation and experiment. High-resolution 3-D volumetric images were generated of an ex vivo rat brain. Images of the cerebellum showed that the white and gray matter tracts could clearly be visualized with isometric resolution in both the azimuth and elevation dimensions.

A single-chip receiver for pulsed laser direct time-of-flight 3-D imaging applications has been realized in a 0.35- $\mu \text{m}$ HV CMOS technology. The chip includes a $32 \times 128$ single-photon avalanche diode (SPAD) array [35% fill factor (FF)] and 257 time-to-digital converters (TDCs) with a ~78-ps resolution. Two adjacent rows ( $2 \times 128$ SPADs) at a time can be selected for simultaneous measurement, i.e., 16 measurement cycles are needed to cover the whole array. SPADs are capable of operating in a gated mode in order to suppress dark and background light-induced detections. The IC was designed to be used in a solid-state 3-D imaging system with laser illumination concentrated in both time (short sub-ns pulses) and space (targeting only the active rows of the SPAD array). The performance of the receiver IC was characterized in a solid-state 3-D range imager with flood-pulsed illumination from a laser diode (LD)-based transmitter, which produced short [~150-ps full-width at half-maximum (FWHM)] high-energy (~3.8-nJ pulse/~14-W peak power) pulses at a pulsing rate of 250 kHz when operating at a wavelength of 810 nm. Two detector/TDC ICs formed an 8k pixel receiver, targeting a field-of-view of $\sim 42^{\circ } \times 21^{\circ }$ by means of simple optics. Frame rates of up to 20 fps were demonstrated with a centimeter-level precision in the case of Lambertian targets within a range of 3.5 m.

In scan-based 3-D systems, the achievable measurement time is strongly restrained by the moving mass. This limitation can be relaxed, by scanning the optical path instead of moving the entire sensor, such that a higher measurement speed can be achieved. This article deals with the design, the control, and the measurement results of a scanning triangulation sensor, in which the illumination and reflection paths of the sensor are scanned by a fast steering mirror (FSM). The system architecture is determined using ray-tracing simulations, such that the performance of the scanning system can be determined in advance. To scan the area of interest with the FSM, conventional raster trajectories and Lissajous trajectories are employed, which provide an early overview of the scan area. For tracking these trajectories, PID and dual-tone controllers are used, respectively. The experimental results demonstrate that for both scan trajectories, the sample can be captured correctly, with a frame rate of 1 frame/s, a maximum spatial resolution of 130 $\mu \text{m}$ , and a field of view of $11.5\,\,\times 18.5\,\,{\mathrm{ mm}}^{2}$ .

Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer.

Accepted: 2018-11-04, 資料番号: SA1190088000

This paper presents an all-electronic Terahertz (THz) 3-D sub-millimeter imaging system based on frequency modulated continuous wave (FMCW), whose frequency ranges from 340GHz to 500GHz. For high-resolution cross-range imaging, the focused method is used instead of the traditional synthetic aperture technique. The imaging performance of the system is verified by some experimental results.

In this paper, a high-resolution 3-D imaging approach for terahertz imaging is proposed. The imaging method is designed for non-focused terahertz time-domain spectroscopy (THz-TDS) systems with a large bandwidth using a cylindrical synthetic aperture. For the evaluation of the method, a complex test object with sub-mm features is considered.

This work describes the design, fabrication, and characterization of a 128-element crossed electrode array in a miniature endoscopic form factor for real-time 3-D imaging. Crossed electrode arrays address some of the key challenges surrounding probe fabrication for 3-D ultrasound imaging by reducing the number of elements required (2N compared with N2). However, there remain practical challenges in packaging a high-frequency crossed electrode array into an endoscopic form factor. A process has been developed that uses a thinly diced strip of flex circuit to bring the back-side connections to common bond surface, which allows the final size of the endoscope to measure only ${6}\,\,\text {mm} \times {5}$ mm. An electrostrictive ceramic composite design was developed for the crossed electrode array. A laser dicing system was used to cut the 1–3 composite as well as etch the array electrode pattern. A single quarter wavelength Parylene matching layer made was vacuum deposited to finish the array. The electrical impedance magnitude of array elements on resonance was measured to be $49~\Omega $ with a phase angle of −55.5°. The finished array elements produced pulses with −6-dB two-way bandwidth of 60% with a 34-MHz center frequency. The average measured electrical crosstalk on the nearest neighboring element and next to nearest neighboring element was −37 and −29 dB, respectively. One- and two-way pulse measurements were completed to confirm the pulse polarity and fast switching speed. Preliminary 3-D images were generated of a wire phantom using the previously described simultaneous azimuth and Fresnel elevation (SAFE) compounding imaging technique.

We report a single-shot surface three-dimensional (3-D) imaging method that uses optical coherence as a contrast mechanism to acquire the vertical (z-direction) information of an object. The illumination of the imaging system comes from a light source with the optical coherence length similar to the depth of field (DoF) of the optical system. Holographic recording is used to retrieve the coherence visibility factor, which is then converted to z-direction information. In the experiment, we compare the imaging results of our method to conventional incoherent imaging results, showing that this contrast mechanism is able to provide additional information. We also validate our 3D imaging results by using axial scanning full-field optical coherence tomography.

In this paper, to deal with the concealed target detection problem, an accurate and efficient algorithm for near-field millimeter wave three-dimensional (3-D) imaging is proposed that uses a two-dimensional (2-D) plane antenna array. First, a two-dimensional fast Fourier transform (FFT) is performed on the scattered data along the antenna array plane. Then, a phase shift is performed to compensate for the spherical wave effect. Finally, fast Gaussian gridding based nonuniform FFT (FGG-NUFFT) combined with 2-D inverse FFT (IFFT) is performed on the nonuniform 3-D spatial spectrum in the frequency wavenumber domain to achieve 3-D imaging. The conventional method for near-field 3-D imaging uses Stolt interpolation to obtain uniform spatial spectrum samples and performs 3-D IFFT to reconstruct a 3-D image. Compared with the conventional method, our FGG-NUFFT based method is comparable in both efficiency and accuracy in the full sampled case and can obtain more accurate images with less clutter and fewer noisy artifacts in the down-sampled case, which are good properties for practical applications. Both simulation and experimental results demonstrate that the FGG-NUFFT-based near-field 3-D imaging algorithm can have better imaging performance than the conventional method for down-sampled measurements.

This paper presents a CMOS image sensor with the in-pixel aperture technique for single-chip 2-D and 3-D imaging. In conventional image sensors, the aperture is located at the camera lens. However, in the proposed image sensor, the aperture is integrated on the CMOS image sensor chip and is formed at a metal layer of the CMOS image sensor (CIS) process. A pixel array of the image sensor is composed of the W, R, B, and PA pixels (W pixel with integrated metal aperture) for extracting color and depth information. While the image of the W pixel becomes blurred with increasing distance from a focused object, the image of the PA pixel maintains the sharpness. Therefore, the depth image can be obtained using the depth from the defocus method. The size of the pixel, which is based on a four-transistor active pixel sensor with pinned photodiode, is $2.8 \,\,\mu {\mathrm{ m}} \times 2.8\,\,\mu \text{m}$ . A prototype of the proposed image sensor was fabricated using the 0.11- $\mu \text{m}$ CIS process and its performance was evaluated.

Compton imaging is a promising imaging modality for radioactive contamination in nuclear facilities. However, most of the Compton cameras in nuclear applications have been constructed with small detector sensors, up to a few centimeters, resulting in low imaging sensitivities. To overcome the limitation and improve imaging sensitivity, in this paper, a Compton camera, named a large-area Compton camera (LACC), was developed using two large-size (27 cm $\times27$ cm) monolithic NaI(Tl) scintillators and 72 square-type photomultiplier tubes. The imaging performance of the LACC was evaluated for surface and internal contamination cases. Our results show that the absolute imaging sensitivity of the LACC was $3.4\times 10^{-5}$ for a 137Cs point source at about 1-m distance in front of the LACC, which is a few $10\times $ higher than those of the existing Compton cameras. The obtained imaging resolution was 14.1° full-width at half-maximum (FWHM) when we use the backprojection algorithm and 5.6° FWHM when we use the maximum-likelihood expectation–maximization algorithm. The LACC also showed the 3-D imaging capability, not only for the surface contamination cases but also for the internal contamination cases within a depth of a few tens of centimeters.

We have developed a new, fast, and simple 3-D imaging approach referred to as Simultaneous Azimuth and Fresnel Elevation (SAFE) compounding using a bias-sensitive crossed-electrode array. The principle behind this technique is to perform conventional plane-wave compounding with a back set of electrodes, while implementing a reconfigurable Fresnel elevation lens with an orthogonal set of front electrodes. While a Fresnel lens would usually result in unacceptable secondary lobe levels, these lobes can be suppressed by compounding different Fresnel patterns. The azimuthal and elevational planes can be simultaneously compounded to increase the beam quality with no loss in frame rate. A 10-MHz, $64 \times 64$ element crossed-electrode relaxor array was fabricated on an electrostrictive one-to-three composite substrate to demonstrate the SAFE compounding approach. The electrostrictive composite array has a measured electromechanical coupling coefficient ( $k_{t}$ ) of 0.62 with a bias voltage of 90 V and a measured two-way pulse bandwidth of 60%. The electrical impedance magnitude of array elements on resonance was measured to be $90~\Omega$ with a phase angle of −35°. Radiation patterns were simulated showing a −6-dB beamwidth of $330~\mu \text{m}$ with secondary lobe levels suppressed more than −60 dB in the azimuth dimension, and a −6-dB beamwidth of $450~\mu \text{m}$ with secondary lobe levels suppressed to −50 dB in the elevation dimension after 64 compounds. Experimental radiation patterns were collected and found to be in good agreement with simulations. Experimental 3-D images of wire phantoms were collected using a Verasonics experimental ultrasound system.

This paper presents a scanning system that integrates a chromatic confocal displacement sensor for topography measurement of a surface. To take an advantage of its compactness and reliability, an off-the-shelf chromatic confocal displacement sensor is integrated. Instead of moving the sensor, a galvanometer scanner reflects the optical point to increase the scan speed, and fast and accurate scanning motion is realized by learning without a model. The resulting images are corrected based on a geometric model to compensate for image distortion.

This paper demonstrates overcoming of the Abbe diffraction limit (ADL) on image resolution. Here, terahertz multispectral reconstructive imaging has been described and used for analyzing nanometer size metal lines fabricated on a silicon wafer. It has also been demonstrated that while overcoming the ADL is a required condition, it is not sufficient to achieve sub-nanometer image resolution with longer wavelengths. A nanoscanning technology has been developed that exploits the modified Beer-Lambert’s law for creating a measured reflectance data matrix and utilizes the “inverse distance to power equation” algorithm for achieving 3-D, sub-nanometer image resolution. The nano-lines images reported herein, were compared to scanning electron microscope (SEM) images. The terahertz images of 70 nm lines agreed well with the transmission electron microscope images. The 14 nm lines by SEM were determined to be ~15 nm. Thus, the wavelength dependent Abbe diffraction limit on image resolution has been overcome. Layer-by-layer analysis has been demonstrated where 3-D images are analyzed on any of the three orthogonal planes. Images of grains on the metal lines have also been analyzed. Unlike electron microscopes, where the samples must be in the vacuum chamber and must be thin enough for electron beam transparency, terahertz imaging is non-destructive, non-contact technique without laborious sample preparation.

Geiger-mode avalanche photodiode (Gm-APD) offers 3D imaging lidar much better capability in terms of detection sensitivity. However, a range walk error (RWE) exists in Gm-APDs which refers to the fluctuation of the measured distance as a function of the intensity of echo pulses. In this paper, we present a real-time restraint method for RWE implemented by unequally intensity-dividing the echo pulses into two Gm-APDs. The difference image of two depth images measured by the divided beams is a matrix of RWE distribution and the intensity image is used to censor the anomalous pixels in the matrix. Combined with the matrix of RWE distribution, an accurate depth image with low RWE can be obtained. Experimental results demonstrate that the proposed method reduces approximately 86% RWE of the conventional method in real time.

International audience; Human inducible pluripotent stem cells (hiPSCs) hold a large potential for disease modeling. hiPSC-derived human astrocyte and neuronal cultures permit investigations of neural signaling pathways with subcellular resolution. Combinatorial cultures, and three-dimensional (3-D) embryonic bodies (EBs) enlarge the scope of investigations to multi-cellular phenomena. The highest level of complexity, brain organoids that-in many aspects-recapitulate anatomical and functional features of the developing brain permit the study of developmental and morphological aspects of human disease. An ideal microscope for 3-D tissue imaging at these different scales would combine features from both confocal laser-scanning and light-sheet microscopes: a micrometric optical sectioning capacity and sub-micrometric spatial resolution, a large field of view and high frame rate, and a low degree of invasiveness, i.e., ideally, a better photon efficiency than that of a confocal microscope. In the present work, we describe such an instrument that uses planar two-photon (2P) excitation. Its particularity is that-unlike two- or three-lens light-sheet microscopes-it uses a single, low-magnification, high-numerical aperture objective for the generation and scanning of a virtual light sheet. The microscope builds on a modified Nipkow-Petráň spinning-disk scheme for achieving wide-field excitation. However, unlike the Yokogawa design that uses a tandem disk, our concept combines micro lenses, dichroic mirrors and detection pinholes on a single disk. This new design, advantageous for 2P excitation, circumvents problems arising with the tandem disk from the large wavelength difference between the infrared excitation light and visible fluorescence. 2P fluorescence excited by the light sheet is collected with the same objective and imaged onto a fast sCMOS camera. We demonstrate 3-D imaging of TO-PRO3-stained EBs and of brain organoids, uncleared and after rapid partial transparisation with triethanolamine formamide (RTF) and we compare the performance of our instrument to that of a confocal laser-scanning microscope (CLSM) having a similar numerical aperture. Our large-field 2P-spinning disk microscope permits one order of magnitude faster imaging, affords less photobleaching and permits better depth penetration than a confocal microscope with similar spatial resolution.

This paper presents a microwave camera design operating in the 20–30 GHz frequency range and capable of producing 3-D images at video frame rate (i.e., real-time), using synthetic aperture radar (SAR) technique. This microwave camera has the potential to provide real-time inspection and diagnosis capabilities in the nondestructive testing, biomedical and security applications, to name a few. The camera utilizes an array composed of a novel array element with built-in dual receivers at its radiating end. The dual receiver design has two significant features particularly important for SAR imaging, namely, it provides for nonuniform spatial sampling, and allows the use of antennas whose sizes are greater than half of the operating wavelength. The camera operates in the monostatic mode where each antenna in the array is used as the transmitting and receiving antenna. A major advantage of this real-time camera design is the simplicity of the microwave circuitry, which reduces the overall size, power consumption, and, cost and renders it portable. The detail design of this wideband microwave 3-D real-time camera is provided along with several images of diverse and complex targets to demonstrate its capabilities and functionality.

A double-curved diverging lens over the flat row–column-addressed (RCA) 2-D array can extend its inherent rectilinear 3-D imaging field of view (FOV) to a curvilinear volume region, which is necessary for applications such as abdominal and cardiac imaging. Two concave lenses with radii of 12.7 and 25.4 mm were manufactured using RTV664 silicone. The diverging properties of the lenses were evaluated based on simulations and measurements on several phantoms. The measured FOV for both lenses in contact with tissue mimicking phantom was less than 15% different from the theoretical predictions, i.e., a curvilinear FOV of $32 {^{\circ }}\times 32^{\circ }$ and $24 {^{\circ }}\times 24^{\circ }$ for the 12.7- and 25.4-mm radii lenses. A synthetic aperture imaging sequence with single-element transmissions was designed for imaging down to 140 mm at a volume rate of 88 Hz. The performance was evaluated in terms of signal-to-noise ratio, FOV, and full-width at half-maximum (FWHM) of a focused beam. The penetration depths in a tissue mimicking phantom with 0.5-dB/(cm $\cdot $ MHz) attenuation were 100 and 125 mm for the lenses with radii of 12.7 and 25.4 mm. The azimuth, elevation, and radial FWHM at 43-mm depth were (5.8, 5.8, 1) $\lambda $ and (6, 6, 1) $\lambda $ . The results of this study confirm that the proposed lens approach is an effective method for increasing the FOV, when imaging with RCA 2-D arrays.

Human inducible pluripotent stem cells (hiPSCs) hold a large potential for disease modeling. hiPSC-derived human astrocyte and neuronal cultures permit investigations of neural signaling pathways with subcellular resolution. Combinatorial cultures, and three-dimensional (3-D) embryonic bodies enlarge the scope of investigations to multi-cellular phenomena. A the highest level of complexity, brain organoids that – in many aspects – recapitulate anatomical and functional features of the developing brain permit the study of developmental and morphological aspects of human disease. An ideal microscope for 3-D tissue imaging at these different scales would combine features from both confocal laser-scanning and light-sheet microscopes: a micrometric optical sectioning capacity and sub-micrometric spatial resolution, a large field of view and high frame rate, and a low degree of invasiveness, i.e., ideally, a better photon efficiency than that of a confocal microscope. In the present work, we describe such an instrument that belongs to the class of two-photon (2P) light-sheet microsocpes. Its particularity is that – unlike existing two- or three-lens designs – it is using a single, low-magnification, high-numerical aperture objective for the generation and scanning of a virtual light sheet. The microscope builds on a modified Nipkow-Petran spinning-disk scheme for achieving wide-field excitation. However, unlike the common Yokogawa design that uses a tandem disk, our concept combines micro lenses, dichroic mirrors and detection pinholes on a single disk. This design, advantageous for 2P excitation circumvents problems arising with the tandem disk from the large wavelength-difference between the infrared excitation light and visible fluorescence. 2P fluorescence excited in by the light sheet is collected by the same objective and imaged onto a fast sCMOS camera. We demonstrate three-dimensional imaging of TO-PRO3-stained embryonic bodies and of brain organoids, under control conditions and after rapid (partial) transparisation with triethanolamine and /ormamide (RTF) and compare the performance of our instrument to that of a confocal microscope having a similar numerical aperture. 2P-virtual light-sheet microscopy permits one order of magnitude faster imaging, affords less photobleaching and permits better depth penetration than a confocal microscope with similar spatial resolution.

A double-curved diverging lens over a flat row– column-addressed (RCA) 2-D array can extend its inherent rectilinear 3-D imaging field-of-view (FOV) to a curvilinear volume region, which is necessary for applications such as abdominal and cardiac imaging. A concave lens with radius of 12.7 mm was manufactured using RTV664 silicone. The diverging properties of the lens were evaluated based on measurements on several phantoms. The measured 6 dB FOV in contact with a material similar to human soft tissue was less than 15% different from the theoretical predictions, i.e., a curvilinear FOV of 32°×32°. A synthetic aperture imaging sequence with single element transmissions was designed for imaging down to 14 cm at a volume rate of 88 Hz. The performance was evaluated in terms of signal-to-noise ratio (SNR), FOV, and full-widthat-half-maximum (FWHM). The penetration depth in a tissue mimicking phantom with 0.5 dB/(cm MHz) attenuation was 13 cm. The results of this study confirm that the proposed lens approach is an effective method for increasing the FOV, when imaging with RCA 2-D arrays.

This paper presents the first fully polarimetric high-resolution circular synthetic aperture radar (CSAR) images at L-band (1.3 GHz). The circular data were acquired in 2008 by the Experimental SAR (E-SAR) airborne system of the German Aerospace Center (DLR) over the airport of Kaufbeuren, Germany. The obtained images resulting from the coherent integration of the whole circular flight are investigated and discussed in terms of two of the main CSAR properties, namely, the theoretical subwavelength resolution in the horizontal plane (x, y) and the 3-D imaging capabilities. The 3-D imaging capabilities are of special interest due to the penetration of L-band in vegetated areas. These results were compared with images processed by the incoherent addition of the full synthetic aperture. The coherent approach showed a better performance since scatterers are focused at their maximum resolution. Due to the nonlinearity of the tracks and the high-computational burden, an efficient fast factorized back-projection (FFBP) has been developed. Unlike frequencydomain processors, it accommodates azimuthal variances and topography changes. Limits and considerations of the proposed algorithm are described and discussed. To further accelerate this process, the FFBP was also implemented in a graphics processing unit (GPU). Processing performance has been assessed with the direct BP (DBP) as a reference, obtaining speedup factors up to 1800. Residual motion errors have been estimated with a new frequency-based autofocus approach for CSAR configurations based on low signal-to-clutter ratio (SCR) isotropic scatterers. High-resolution images of man-made and distributed scatterers have been analyzed and compared with a stripmap SAR, both concerning anisotropic and isotropic-like scatterers. Results include a single-channel tomogram of a Luneburg lens and a fully polarimetric tomogram of a tree.

This paper demonstrates the fabrication, characterization, and experimental imaging results of a 62+62 element λ/2-pitch row-column-addressed capacitive micromachined ultrasonic transducer (CMUT) array with integrated apodization. A new fabrication process was used to manufacture a 26.3 mm by 26.3 mm array using five lithography steps. The array includes an integrated apodization, presented in detail in Part I of this paper, which is designed to reduce the amplitude of the ghost echoes that are otherwise prominent for row-column-addressed arrays. Custom front-end electronics were produced with the capability of transmitting and receiving on all elements, and the option of disabling the integrated apodization. The center frequency and -6-dB fractional bandwidth of the array elements were 2.77 ± 0.26 MHz and 102 ± 10%, respectively. The surface transmit pressure at 2.5 MHz was 590 ± 73 kPa, and the sensitivity was 0.299 ± 0.090 V/Pa. The nearest neighbor crosstalk level was -23.9 ± 3.7 dB, while the transmit-to-receive-elements crosstalk level was -40.2 ± 3.5 dB. Imaging of a 0.3-mm-diameter steel wire using synthetic transmit focusing with 62 single-element emissions demonstrated axial and lateral FWHMs of 0.71 mm and 1.79 mm (f-number: 1.4), respectively, compared with simulated axial and lateral FWHMs of 0.69 mm and 1.76 mm. The dominant ghost echo was reduced by 15.8 dB in measurements using the integrated apodization compared with the disabled configuration. The effect was reproduced in simulations, showing a ghost echo reduction of 18.9 dB.

A standoff 3-D imaging radar based on 4Tx-16Rx MIMO array at 340 GHz is presented for security body scanning. FMCW signals with 20 GHz bandwidth were electronically beam formed by the array in horizontal dimension and focused to narrow beam lines by an elliptic cylinder in elevation. Experiment results indicated that the imaging resolutions at a distance of 4-m are about 14-mm, 12mm, and 10mm in horizontal, vertical, and range dimension, respectively. With a fast scanning mirror, 4 Hz frame rate is now possible with a field of view of 2m×0.8m.

We report a novel fusion of droplet microfluidics and light-sheet microscopy, to achieve high-throughput sample compartmentalization, manipulation and three-dimensional imaging on a chip. This optofluidic device characterized by orthogonal plane illumination and rapid liquid handling is compact and cost-effective, and capable of preparing sample droplets with tunable size, frequency and ingredient. Each droplet flowing through the device's imaging region is self-scanned by a laser-sheet, three-dimensionally reconstructed and quantitatively analysed. This simple-and-robust platform combines fast 3-D imaging with efficient sample preparation and eliminates the need of a complicated mechanical scan at the same time. Achieving 500 measurements per second and screening over 30 samples per minute, it shows great potential for various lab-on-a-chip biological studies, such as embryo sorting and cell growth assays.

We describe cameras incorporating focal plane arrays of Geiger-mode avalanche photodiodes (GmAPDs) that enable 3-D imaging in laser radar (LADAR) systems operating at wavelengths near 1.0 and 1.5 μm. GmAPDs based on the InGaAsP material system achieve single-photon sensitivity at every pixel of the array and are hybridized to custom CMOS ROICs providing 0.25 ns timing resolution. We present camera-level performance for photon detection efficiency and dark count rate, along with a survey of the evolution of performance for a substantial number of 32 × 32 cameras. We then describe a temporal statistical analysis of the array-level dark count behavior that distinguishes between Poissonian intrinsic dark count rate and non-Poissonian crosstalk counts. We also report the spatial analysis of crosstalk events to complement the statistical temporal analysis. Differences between cameras optimized for the two different wavelengths—1.0 and 1.5 μm—are noted, particularly with regard to crosstalk behavior.

Constructing a double-curved row-column-addressed (RCA) 2-D array or applying a diverging lens over the flat RCA 2-D array can extend the imaging field-of-view (FOV) to a curvilinear volume without increasing the aperture size, which is necessary for applications, such as abdominal and cardiac imaging. Extended FOV and low channel count of double-curved RCA 2-D arrays make 3-D imaging possible with equipment in the price range of conventional 2-D imaging. This paper proposes a delay-and-sum beamformation scheme specific to double-curved RCA 2-D arrays and validates its focusing ability based on simulations. A synthetic aperture imaging sequence with single element transmissions is designed for imaging down to 14 cm at a volume rate of 88 Hz. Using a diverging lens with an f-number of −1 circumscribing the underlying RCA array, the imaging quality of a double-curved $\lambda /2$ -pitch 3-MHz 62 + 62 RCA 2-D array is investigated as a function of depth within a curvilinear FOV of 60 $^{\circ }\times 60^{\circ }$ . The simulated double-curved 2-D array exhibits the same full-width-at-half-maximum values for a point scatterer within its curvilinear FOV at a fixed radial distance compared with a flat 2-D array within its rectilinear FOV. The results of this paper demonstrate that the proposed beamforming approach is accurate for achieving correct time-of-flight calculations, and hence avoids geometrical distortions.

It has been shown that row–column-addressed (RCA) 2-D arrays can be an inexpensive alternative to fully addressed 2-D arrays. Generally imaging with an RCA 2-D array is limited to its forward-looking volume region. Constructing adouble-curved RCA 2-D array or applying a diverging lens over the flat RCA 2-D array, can extend the imaging field-of-view (FOV) to a curvilinear volume without increasing the aperture size, which is necessary for applications such as abdominal and cardiac imaging. Extended FOV and low channel count of doublecurved RCA 2-D arrays make it possible to have 3-D imaging with equipment in the price range of conventional 2-D imaging. This study proposes a delay-and-sum (DAS) beamformation scheme specific to double-curved RCA 2-D arrays and validates its focusing ability based on simulations. A synthetic aperture imaging (SAI) sequence with single element transmissions at a time, is designed for imaging down to 14 cm at a volume rate of 88 Hz. The curvilinear imaging performance of a λ/2-pitch 3 MHz 62+62 RCA 2-D array is investigated as a function of depth, using a diverging lens with f-number of -1. The results of this study demonstrate that the proposed beamforming approach is accurate for achieving correct time-of-flight calculations, and hence avoids geometrical distortions.

Terahertz (THz) imaging technology has been widely applied to the fields of security inspection, nondestructive testing. In this paper, the application of nonuniform fast Fourier transform(NUFFT)to the developed THz 3-D imaging system, which combines the advantages of THz and frequency modulation continuous wave (FMCW) signal, is investigated. The presented image reconstruction algorithm can increase computational efficiency compared with the conventional Omega-K (ωK) algorithm. The experimental results are illustrated to demonstrate the developed THz FMCW 3-D imaging system and the presented imaging method.

This paper proposes a three-step method for high-resolution three-dimensional imaging of group rotating targets in uniform linear motion. In the first step, motion compensation is performed simultaneously with the whole target set. Then, the matched filter is designed to estimate the coordinates of scattering centers. Finally, the anisotropy of dominant scattering centers is described via phase compensation. Simulation results have proved the validity of the proposed method.

Through-the-wall imaging techniques with ultrawideband (UWB) radars are promising candidates for non-destructive testing and reliable human detection, especially in disaster areas, where victims are buried under collapsed walls. These applications require high-resolution target imaging to identify the object shape, such as a human body. We have already proposed a high-quality 3-dimensional (3-D) imaging algorithm in the form of envelope that is aimed at near field sensing for non-contact measurement or target identification for robots. Envelope achieves real-time accurate 3-D imaging with group mapping from multiple observed ranges to target points, and offers a reliable image even in noisy situations. However, this method does not maintain its quality for through-the-wall imaging because an observed range shift due to wall penetration causes a serious distortion in the image. This paper presents a high-resolution 3-D imaging algorithm by modifying the original envelope, and which gives a more accurate object shape behind a wall. Furthermore, to enhance the resolution of the estimated images, this method is combined with a direct waveform compensation method, known as spectrum offset correction. Numerical simulations and an experiment verify that our proposed method achieves high-resolution 3-D imaging for through-the-wall radar applications.

Millimeter wave Near-field 3-D imaging has great importance on security applications for its penetrating characteristics and the 3-D information of the target. To obtain accurate and high resolution images, we propose a direct 3-D integral method to reconstruct the 3-D images. The algorithm directly processes the scattered data without any interpolation or approximation, making it more accurate than the conventional holographic method. Experiments using simulated data verify the feasibility of the proposed method.

Bistatic inverse synthetic aperture radar (BiISAR) imaging provides complementary information to monostatic ISAR imaging. A suggestion that the conventional bistatic ISAR can be replaced by an equivalent monostatic radar is shown to be inadequate in this paper. We prove that the BiISAR image is a sheared version of the projection of the target on the range-Doppler plane. A bistatic interferometric radar configuration is proposed to correct this distortion and to form 3-D image. Simulation results have validated our analysis and shown the viability of the proposed 3-D imaging algorithm.

The light intensity distributions in the front space of a contact-type multiview 3-D imaging system are measured to estimate the effects of the differences in real and nominal values of parameters and alignment errors on the quality of 3-D images. The distributions clearly reveal how the viewing zone cross section is formed and how the mixed images are formed. For these measurements, a 1×4 Fresnel lens array and a projector are used as the viewing zone forming optics and image source, respectively. The results are graphically represented in terms of crosstalk. Both the misalignments and the inaccuracies greatly increase the crosstalk.

This talk will present our recent work in super-resolution optical microscopy, including techniques for 3-D super-resolution optical imaging, multiparticle parallel localization and tracking in transparent sample, as well as super-resolution time-resolved imaging.

Nondestructive three-dimensional imaging of femtosecond laser-written buried structures is demonstrated using optical coherence microscopy providing lateral and depth resolution on a micron scale. This high speed technique, which requires no sample preparation, enables the visualization of volumetric structural modification created deep in transparent dielectric medium with high signal/noise contrast. Images of buried void structures with dimensions as large as 190 μm in length were obtained without shadowing effects impugning the image fidelity.

This paper describes the design and characterization of a 134-pixel linear array sensor for three-dimensional measurements based on both multiple-pulse indirect-time-of-flight (ITOF) and optical triangulation (OT) techniques. In OT mode, a winner-take-all (WTA) stage allows for a fast localization of the spot position along the pixel array so that only useful pixels are selectively read out, for a maximum operation speed of 131 kVoxel/s. Distance measurements in OT mode over the range 0.4 m-1.0 m are obtained with a best precision of 0.004%-0.21%, while ITOF operation allows mapping the range 0.8-3 m at 125 voxel/s with a relative precision of 1.7%-3.8%. Background rejection up to 10 klux has also been demonstrated without the need of any optical filters.

This guest editorial introduces the special section on Light Field and Holographic Displays.

It has been suggested that 3 to 5% of total lung cancer deaths in the UK may be associated with elevated radon concentration. Radon gas levels can be assessed using CR-39 plastic detectors which are often assessed by 2-D image analysis of surface images. 3-D analysis has the potential to provide information relating to the angle at which alpha particles impinge on the detector. In this study we used a "LEXT" OLS3100 confocal laser scanning microscope (Olympus Corporation, Tokyo, Japan) to image tracks on five CR-39 detectors. We were able to identify several patterns of single and coalescing tracks from 3-D visualisation. Thus this method may provide a means of detailed 3-D analysis of Solid State Nuclear Track Detectors.

A structured light pattern can be used to acquire the range data of an object from a single camera for 3-D imaging systems and it can be used for practical applications in a dynamic environment, i.e., a scene with moving objects. This paper illustrates the generation of a class of distinct structured light patterns with various sizes (range image points).

In color digital holography the recording and reconstruction of three holograms, by an optical setup operating in multi-wavelength mode, is necessary. Incorrect superposition of different images at various wavelengths may occur due to the presence of chromatic aberrations. We demonstrate that the compensation of the chromatic aberrations can be achieved by using all of the information contained in the multi-wavelength digital holograms. Chromatic aberration is extracted from phase maps reconstructed at different wavelengths, resulting in perfect full color amplitude reconstructions. The method has important applications in color 3-D holographic imaging and display.

Current biological and medical research is aimed at obtaining a detailed spatiotemporal map of a live cell's interior to describe and predict cell's physiological state. We present here an algorithm for complete 3-D modelling of cellular structures from a z-stack of images obtained using label-free wide-field bright-field light-transmitted microscopy. The method visualizes 3-D objects with a volume equivalent to the area of a camera pixel multiplied by the z-height. The computation is based on finding pixels of unchanged intensities between two consecutive images of an object spread function. These pixels represent strongly light-diffracting, light-absorbing, or light-emitting objects. To accomplish this, variables derived from R\'{e}nyi entropy are used to suppress camera noise. Using this algorithm, the detection limit of objects is only limited by the technical specifications of the microscope setup--we achieve the detection of objects of the size of one camera pixel. This method allows us to obtain 3-D reconstructions of cells from bright-field microscopy images that are comparable in quality to those from electron microscopy images., Comment: 41 pages, 3 figures

In optical time-of-flight (TOF) range imaging, harmonic intensity modulation of the illumination source is very common. By detecting the phase delay between emitted and reflected sinusoids, the distance can be measured accurately. However, this harmonic approach does not allow for the concurrent operation of several TOF range cameras because the arbitrary superposition of several differently parametrized sinusoids leads to a sinusoid with incorrect phase. To minimize inaccuracies by multi-camera interference (MCI), pseudonoise (PN) modulated intensity signals are employed for robust TOF range imaging. The time of flight is locally measured by correlating the incident light intensity with two time-shifted versions of the PN sequence, making use of smart demodulation pixels. We derive two fundamental expressions for the basic limitations of TOF measurements using PN sequences. Firstly, the precision of the distance measurement is limited by photon shot noise, and it essentially shows an inverse square root dependence of the number of detected photoelectrons. Secondly, MCI causes an inaccurate distance measurement given as the ratio of two sums. The denominator is the sum of two autocorrelation and two cross-correlation values; the nominator is the sum of one autocorrelation and one cross-correlation value. Due to the lack of a strict mathematical theory of correlation properties of m-sequences, an exhaustive numerical simulation was carried out to obtain expectation values of the distance measurement inaccuracy as a function of the sequence length and the number of interfering cameras. For experimental verification, an image sensor with 176 times 144 demodulation pixels was manufactured with a standard CMOS process offering a CCD option. Measurements taken with up to five concurrently operating sensors were in excellent agreement with our theoretical predictions concerning achievable distance accuracy. This confirms the aptness of PN techniques for multi-camera optical TOF range imaging.

andEdwin L. Thomas*Department of Materials Science and Engineering,Massachusetts Institute of Technology, Cambridge,Massachusetts 02139ReceiVed May 20, 2007ReVised Manuscript ReceiVed July 6, 2007Block copolymers (BCPs) exhibit various periodic structurescreated through microphase separation with tunable size andshape of microdomains via choice of molecular weight,composition, and chain architecture and with the addition ofplasticizers or homopolymers.

Link to the publisher version: https://ieeexplore.ieee.org/document/7112180; International audience; The internal structure of a sample of an absorber is retrieved from its measured scattered field. By its very nature, this target is a very weak-scatterer as it is used to cover the walls in anechoic chambers. The real part of its permittivity is rather small but its dielectric losses are non negligible. Quantitative maps of the complex permittivity of the sample were obtained from monochromatic scattered fields measured inside an anechoic chamber in a multistatic configuration. An imaging procedure taking into account the noise characteristics disturbing the measurements was used for this purpose.