Reflection-mode Imaging Research Articles

Array of 296-GHz CMOS Concurrent Transceiver Pixels With Phase and Amplitude Extraction Circuits for Improving Reflection-Mode Imaging Resolution

Array of 296-GHz CMOS Concurrent Transceiver Pixels With Phase and Amplitude Extraction Circuits for Improving Reflection-Mode Imaging Resolution

Nondestructive evaluation of mechanical heart valve disc thickness degradation due to accelerated durability test using THz-TDS measurements

ABSTRACT Quality assurance and control during the mechanical heart valve components’ production process is paramount to mitigate most of the valve-related complications arising from valve replacement. Nondestructive evaluation of heart valve implants with complex profiles during production is challenging due to the biocompatibility requirements and clean room assembly conditions. This study first tested the UHMWPE disc of TTK Chitra mechanical heart valve models TC1 and TC2 using Terahertz imaging in reflection mode. The UHMWPE discs were raster scanned in X-Y directions to obtain a Terahertz-C scan to locate the macro defects due to wear out, and to distinguish between the true positive and true negative samples. The results were verified with digital microscope studies. Second, this study investigates a unique relationship between Terahertz imaging in reflection mode and heart valve disc degradation due to accelerated durability study. Third, the variation of disc surface roughness due to accelerated durability test was studied by Gaussian curve fitting analysis of fast Fourier transform of the Terahertz reflections. Finally, a comparison between the TC1 and TC2 heart valve model’s wear-out foot print was carried out using Terahertz C-scan. Our results imply that Terahertz time-domain spectroscopy has promising applications in NDE measurements of biocompatible implants.

Nondestructive evaluation of cork phenolic-based aerospace structure using Terahertz time domain spectroscopy and imaging

ABSTRACT Cork phenolic sheets with thermal protection paints are used as thermal protection system in launch vehicles. Detecting debonds and inclusions at the interface of cork phenolic-composite structure and thickness measurement of multi-layer TPS is highly challenging with single-side access. In this study, Terahertz imaging in reflection mode is used to detect the defects. The sample is raster scanned in X-Y directions, and the reflected signal is measured at each pixel and consolidated to obtain a Terahertz C-scan image of the entire area. The image obtained using Terahertz time-domain spectroscopy imaging system can distinguish between the healthy and debond/inclusion areas. Terahertz time-domain spectroscopy in transmission mode is carried out to obtain the refractive index and absorption coefficient of individual layers, which is a prerequisite for thickness measurement. The time-of-flight principle is used for thickness estimation of multi-layer thermal protection systems over carbon fibre reinforced plastic samples. The Sparse deconvolution technique is used to resolve the overlapping echoes to obtain the time delay for each layer. The thickness values obtained for cork phenolic sheet and red and white thermal protection paints over carbon fibre-reinforced plastic samples using Terahertz-time domain spectroscopy are in close agreement with the actual values.

Perspective on active submillimeter electromagnetic wave imaging using CMOS integrated circuits technologies

The performance of CMOS transmitters and receivers operating at the submillimeter electromagnetic wave frequencies have sufficiently improved for use in active transmission and reflection-mode imaging applications that have the potential for broad deployment and utilization. Imaging integrated circuits have the potential to be large in area to support a high number of pixels along with digital backend processing circuits. For high volume imaging applications that may eventually be included in automobiles, smartphones, laptops, tablets, and others, a large manufacturing capacity to support the volume of large area ICs is necessary. For this, the use of CMOS technologies with a much larger manufacturing capacity is favored. It should be possible to improve the performance of CMOS circuits to increase the range, and operation margin and frequency. The electronically steerable submillimeter-wave reflector technology holds the promise for improving the performance and energy efficiency of submillimeter-wave imaging systems by multiple orders of magnitude, and it is a critical research area. Increasing the operating frequency from 430 to 850 GHz using CMOS integrated circuits to improve the angular resolution by 2X at a given form factor (∼0.15° for a reflector diameter of 15 cm) can make the submillimeter-wave imaging competitive to the LIDAR angular-resolution performance, while providing superior capabilities in visually impaired conditions and making the imaging devices more affordable.

Single-shot wide-field imaging in reflection by using a single multimode fiber

A single multimode fiber (MMF) provides almost an ideal optical channel to constitute a hair-thin endoscope for minimally invasive biomedical imaging at depths in tissue, especially if the imaging operation can be performed with one single shot in reflection mode, which, however, remains challenging to date. In this work, we present single-shot wide-field reflectance imaging by using a single MMF as the illumination unit and imaging probe simultaneously. To achieve single-shot image capture, a reflection matrix of the fiber was built by a learning-assisted approach for the universal inverse conversion from the output amplitudes to the input amplitudes. The performance was tested by imaging more than 30 000 natural scenes projected by a digital micromirror device, and an averaged Pearson correlation coefficient over 0.84 with respect to the ground truth was achieved in the experiment. Furthermore, the ability to image dynamic scenes at a high frame rate of up to 180 frames per second was demonstrated together with real-time observation of a freely moving microneedle located at the distal end of the MMF. The proposed reflection-mode single-fiber imaging scheme paves the way for practical video-rate microendoscopy at depths in tissue in a minimally invasive manner.

Focused vortex and imaging full-space metasurface

Due to their abilities to adjust the electromagnetic wavefront in both transmission and reflection modes without changing the structure, the full space metasurfaces has attracted extensive attention. However, it is still a challenge to achieve full-space multi-functionalities within a simple metasurface structure. Herein, we proposed a full space metasurface by utilizing a two kinds of medium substrate layers all-dielectric-atom for the right circularly polarized (RCP) and linear polarization (LP) incidences at two distinct operation frequencies. The all-dielectric-atom consists of subwavelength-thickness polyimide and vanadium dioxide (VO2) substrate layer and mushroom-shaped silicon pillar with a period of 100μm. Based on the emerging all-dielectric-atom, the designed multifunctional full space metasurface generates deflection focusing, deflection vortex, focusing vortex, and imaging in both transmission and reflection modes, respectively. Our designed structure not only improves the control space for terahertz wave, but also realizes the linear polarization wave imaging function, which has great potential in terahertz communication and security inspection imaging.

Lensless Short-Range Reflection-Mode Imaging at 275 GHz Using CMOS Concurrent Transceivers

Lensless short-range reflection-mode imaging through a cardboard cover is demonstrated at 275 GHz using a pair of concurrent complimentary metal–oxide–semiconductor transceiver pixels separated by ∼5 mm on a printed circuit board (PCB). This is the first such demonstration at frequencies above 100 GHz. The separation between the imaged object and pixels is ∼1 cm and the operation at 275 GHz allows the lateral resolution to be reduced to ∼2 mm due to a smaller wavelength. A concurrent transceiver pixel incorporating a transmitter with an effective isotropic radiated power of −18.9 dBm and a receiver with a double sideband noise figure of ∼51 dB in an area of 0.45 × 0.49 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is used. The reflected signals from a target must be greater than the transmitted signal directly coupled to the receiver, and this isolation between the transmitter and receiver limits the imager range and contrast. Full-wave electromagnetic simulations (ANSYS high-frequency structure simulator (HFSS)) of a PCB with a transmit and receive rectangular patch antenna with a separation of ∼5 mm show that ∼65 dB isolation at 275 GHz can be achieved. This should be sufficient to image a target with a radar cross section of 2 mm × 2 mm with a reflection coefficient of 0.1 that is 1-cm away. This work points to a path for incorporation of millimeter and submillimeter wave imaging in a handheld device.

DIAGNÓSTICO E TREINAMENTO POR TECNOLOGIA DE IMAGEM EM TRAUMATISMOS DO JOELHO NO BASQUETEBOL

ABSTRACT Introduction: The research and development of new methods of injury diagnosis and rehabilitation training in benefits to the health and training of athletes is a contemporary priority. Among modern techniques, diagnostic imaging technology stands out. Objective: Study the auxiliary effect of imaging technology in the diagnosis and rehabilitation training of functional knee joint injuries in basketball practice. Methods: 50 basketball players diagnosed and treated in the past four years for knee joint function injuries in a special hospital were selected, including 28 male and 22 female athletes, aged 17 to 25 years. PerkinElmer Spotlight-300 FTIR spectral imaging system was used to scan the articular cartilage sections, visible light and total absorption images of the samples were obtained by reflection mode imaging. Results: The peak infrared feature of the articular cartilage measured by the infrared spectrum imaging technology is very consistent with the FTIR spectrum. After rehabilitation training, the Y test score of female patients increased from 96.72 ± 6.05 to 105.40 ± 4.23, and the Y test score of male patients increased from 98.34 ± 5.33 to 105.51 ± 4.89, showing significant differences. Conclusion: Infrared spectrum imaging technology is an effective technique for identifying functional knee joint injury, and is of great use for diagnosis and training update in basketball players with knee trauma. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Compressed ultrahigh-speed single-pixel imaging by swept aggregate patterns

Single-pixel imaging (SPI) has emerged as a powerful technique that uses coded wide-field illumination with sampling by a single-point detector. Most SPI systems are limited by the refresh rates of digital micromirror devices (DMDs) and time-consuming iterations in compressed-sensing (CS)-based reconstruction. Recent efforts in overcoming the speed limit in SPI, such as the use of fast-moving mechanical masks, suffer from low reconfigurability and/or reduced accuracy. To address these challenges, we develop SPI accelerated via swept aggregate patterns (SPI-ASAP) that combines a DMD with laser scanning hardware to achieve pattern projection rates of up to 14.1 MHz and tunable frame sizes of up to 101×103 pixels. Meanwhile, leveraging the structural properties of S-cyclic matrices, a lightweight CS reconstruction algorithm, fully compatible with parallel computing, is developed for real-time video streaming at 100 frames per second (fps). SPI-ASAP allows reconfigurable imaging in both transmission and reflection modes, dynamic imaging under strong ambient light, and offline ultrahigh-speed imaging at speeds of up to 12,000 fps.

High‐Speed All‐Fiber Micro‐Imaging with Large Depth of Field

AbstractSingle fiber imaging has evolved into a powerful method for detecting minute objects in narrow spaces. However, existing systems are not conducive to imaging dynamic objects at depth due to their bulky probes, time‐consuming scanning acquisition methods, and transmissive illumination mode. Minimally invasive reflection mode imaging with high spatial and temporal resolution remains an open challenge. Here, a precise and high‐speed imaging scheme without scanning is proposed. Multimode fiber imaging technology is incorporated into an all‐fiber aberration‐free precision detection system. High temporal resolution (5000 fps) detection of tiny natural scenes is experimentally realized by optimizing the approximation of the inverse transmission matrix in a simple and compact setup. The system can display the detected screen in real‐time and the computational imaging with a large depth of field (1 mm) is enabled by jointly learning. The recovery results are superior compared to typical deep neural networks. The demonstrated scheme offers a new possibility for many applications, for example, microendoscopy, all‐optical computing, and remote high‐speed video transmission.

Soft X-ray Lensless Imaging in Reflection Mode

We report on the development and implementation of methodologies dedicated to soft X-ray imaging by coherent scattering in reflection mode. Two complementary approaches are tested, based on Fourier transform holography and on ptychography. A new method for designing holographic masks has been developed. Our results represent a feasibility test and highlight the potential and limitations of imaging in reflection mode. Reflectivity is less efficient than transmission at soft X-ray wavelengths, hampering the acquisition of good quality images. Nonetheless, it has the potential to image a wider set of samples, notably those that are not transparent to soft X-rays. Although the images obtained so far are of modest quality, these results are extremely encouraging for continuing the development of coherent soft X-ray imaging in reflection mode.

Three-dimensional transfer function of optical microscopes in reflection mode.

Three-dimensional (3D) transfer functions build the basis for a comprehensive characterization of optical imaging systems in the spatial frequency domain. Utilizing the projection-slice theorem, the 2D modulation transfer function of an incoherent imaging system can be derived from a 3D transfer function by integration with respect to the axial spatial frequency. For a diffraction limited microscope with homogeneous incoherent pupil illumination, the modulation transfer function equals the 2D autocorrelation function of a circular disc. However, until now to the best of our knowledge no 3D transfer function has been published, which exactly leads to the 2D modulation transfer function of a diffraction limited microscope in reflection mode. In this article, we derive a formula, which after integration with respect to the axial spatial frequency coordinate perfectly fits to the diffraction limited 2D modulation transfer function. The inverse three-dimensional Fourier transform of the 3D transfer function results in a complex-valued 3D point spread function, from which the depth of field, the lateral resolution and, in addition, the corresponding 3D point spread function of both, a conventional and an interference microscope, can beobtained.

Complementary LEEM and eV-TEM for imaging and spectroscopy

Transmission electron microscopy at very low energy is a promising way to avoid damaging delicate biological samples with the incident electrons, a known problem in conventional transmission electron microscopy. For imaging in the 0-30 eV range, we added a second electron source to a low energy electron microscopy (LEEM) setup, enabling imaging and spectroscopy in both transmission and reflection mode at nanometer (nm) resolution. The latter is experimentally demonstrated for free-standing graphene. Exemplary eV-TEM micrographs of gold nanoparticles suspended on graphene and of DNA origami rectangles on graphene oxide further establish the capabilities of the technique. The long and short axes of the DNA origami rectangles are discernable even after an hour of illumination with low energy electrons. In combination with recent developments in 2D membranes, allowing for versatile sample preparation, eV-TEM is paving the way to damage-free imaging of biological samples at nm resolution.

High-Power Lensless THz Imaging of Hidden Objects

The potential of pulsed THz radiation for time-of-flight imaging applications is well recognized. However, advances in this field are currently severely limited by the low average power of ultrafast THz sources. Typically, this results in impractically long acquisition times and a loss in resolution and contrast. These limitations make imaging of the objects in real-life scenarios impossible. Here, conclusively, the potential of state-of-the-art high-average power THz time-domain spectrometer (TDS), driven by a 100-W class, one-box ultrafast oscillator for imaging applications is shown by demonstrating lensless THz imaging in reflection mode of a dielectric sample with low reflectivity. Images obtained with our home-built 20-mW average power THz-TDS system show a significant contrast enhancement compared to a state-of-the-art commercial THz-TDS with less than $200~\mu \text{W}$ of average power. Our unique setup even allows us to obtain images of such an object with high-contrast hidden inside a medium-density fiberboard (MDF) box. This opens the door to THz time-of-flight imaging of concealed objects of unknown shape and orientation in various real-life scenarios which were so far impossible to realize.

Material characterisation of a painted beehive panel by advanced spectroscopic and chromatographic techniques in combination with hyperspectral imaging

In this study, a painted beehive panel from the collection of the Slovene Ethnographic Museum was examined with respect to its material composition with the aim to reveal the painting technique. Due to the state of degradation due to outdoor weathering (UV irradiation, rainfall, extreme temperature and humidity fluctuations), as well as past conservation interventions, the object represented a complex analytical challenge. We aimed for non-invasive techniques (FTIR in reflection mode, Raman spectroscopy and hyperspectral imaging in the range of 400–2500 nm); however, in order to explore paint layers, cross-sections were also analysed using Raman spectroscopy. FTIR spectroscopy in transmission mode and gas chromatography coupled to mass spectrometry were also used on sample fragments. Various original materials were identified such as pigments and binders. The surface coating applied during conservation interventions was also characterised. Additionally, organic compounds were found (oxalate, carboxylate), representing transformation products. The potential use of Prussian blue as a background paint layer is discussed.

Reflection-mode virtual histology using photoacoustic remote sensing microscopy

Histological visualizations are critical to clinical disease management and are fundamental to biological understanding. However, current approaches that rely on bright-field microscopy require extensive tissue preparation prior to imaging. These processes are both labor intensive and contribute to creating significant delays in clinical feedback for treatment decisions that can extend to 2–3 weeks for standard paraffin-embedded tissue preparation and interpretation, especially if ancillary testing is needed. Here, we present the first comprehensive study on the broad application of a novel label-free reflection-mode imaging modality known as photoacoustic remote sensing (PARS) for visualizing salient subcellular structures from various common histopathological tissue preparations and for use in unprocessed freshly resected tissues. The PARS modality permits non-contact visualizations of intrinsic endogenous optical absorption contrast to be extracted from thick and opaque biological targets with optical resolution. The technique was examined both as a rapid assessment tool that is capable of managing large samples (> 1 cm2) in under 10 min, and as a high contrast imaging modality capable of extracting specific biological contrast to simulate conventional histological stains such as hematoxylin and eosin (H&E). The capabilities of the proposed method are demonstrated in a variety of human tissue preparations including formalin-fixed paraffin-embedded tissue blocks and unstained slides sectioned from these blocks, including normal and neoplastic human brain, and breast epithelium involved with breast cancer. Similarly, PARS images of human skin prepared by frozen section clearly demonstrated basal cell carcinoma and normal human skin tissue. Finally, we imaged unprocessed murine kidney and achieved histologically relevant subcellular morphology in fresh tissue. This represents a vital step towards an effective real-time clinical microscope that overcomes the limitations of standard histopathologic tissue preparations and enables real-time pathology assessment.

Reflection-mode acousto-optic imaging using a one-dimensional ultrasound array with electronically scanned focus.

.Significance: Practical implementation of acousto-optic imaging (AOI) encounters difficulties that prevent it from rapid adoption in clinical use. In many practical medical applications, the region of interest may be accessed only from one side, and using a water tank for coupling is not feasible. The solution might be to use reflection-mode imaging with an electronically scanned ultrasound (US) focus. Such an approach, however, entails considerable challenges.Aim: The possibilities of detecting and localizing light-absorbing inclusions inside turbid media by combining reflection-mode AOI conducted using a one-dimensional US array with electronic scanning of the US focus are investigated experimentally and signal processing algorithms that could be used for this purpose are introduced.Approach: We determine the speckle contrast decrease due to the acousto-optic effect as a function of the US focal point coordinates. Different signal postprocessing techniques are investigated.Results: A significant decrease in the determined speckle contrast difference values is observed due to the presence of light-absorbing inclusions. However, local minima occur in the plots only under specific conditions. Subtracting individual distributions and determining symmetry deviations allow for localizing the inclusions.Conclusions: Detection and localization of optically distinct regions are possible using the introduced approach. Signal postprocessing is required in a general case.

Holographic scanning confocal microscopy for both reflected light and fluorescence light imaging

In this paper, we propose a holographic scanning based confocal microscope that works in both the reflection and fluorescence modes. Here, the illumination beam is scanned using a reconfigurable binary hologram instead of a usual galvanometer mirror scanner. The reconfigurable hologram is implemented using a liquid crystal spatial light modulator. Two different lasers are used for fluorescence and reflection mode imaging with the phase profile of the illumination beam, derived from each laser, described by the holograms. We demonstrate the working of our microscope in both the modes by imaging a section of tooth specimen stained with a fluorescent dye.

Reflection-mode continuous-wave 0.15λ-resolution terahertz solid immersion microscopy of soft biological tissues

We have developed a method of terahertz (THz) solid immersion (SI) microscopy for continuous-wave reflection-mode imaging of soft biological tissues with a sub-wavelength spatial resolution. In order to achieve strong reduction in the dimensions of the THz beam caustic, an electromagnetic wave is focused into the evanescent field volume behind a medium with a high refractive index. We have experimentally demonstrated a 0.15λ-resolution of the proposed imaging modality at λ = 500 μm, which is beyond the Abbe diffraction limit and represents a considerable improvement over the previously-reported arrangements of SI imaging setups. The proposed technique does not involve any sub-wavelength near-field probes and diaphragms, thus, avoiding the THz beam attenuation due to such elements. We have applied the developed method for THz imaging of various soft tissues: a plant leaf blade, cell spheroids, and tissues of the breast ex vivo. Our THz images clearly reveal sub-wavelength features in tissues, therefore, promising applications of THz SI microscopy in biology and medicine.

Removal of back-reflection noise at ultrathin imaging probes by the single-core illumination and wide-field detection

Thin waveguides such as graded-index lenses and fiber bundles are often used as imaging probes for high-resolution endomicroscopes. However, strong back-reflection from the end surfaces of the probes makes it difficult for them to resolve weak contrast objects, especially in the reflectance-mode imaging. Here we propose a method to spatially isolate illumination pathways from detection channels, and demonstrate wide-field reflectance imaging free from back-reflection noise. In the image fiber bundle, we send illumination light through individual core fibers and detect signals from target objects through the other fibers. The transmission matrix of the fiber bundle is measured and used to reconstruct a pixelation-free image. We demonstrated that the proposed imaging method improved 3.2 times on the signal to noise ratio produced by the conventional illumination-detection scheme.