Long-range Imaging Research Articles

Co-analysis of Brain Structure and Function using fMRI and Diffusion-weighted Imaging

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when studying the brain, as the functional role that a brain area fulfills may be largely defined by its connections to other brain areas. In this report, we describe a novel, non-invasive approach for relating brain structure and function using magnetic resonance imaging (MRI). This approach, a combination of structural imaging of long-range fiber connections and functional imaging data, is illustrated in two distinct cognitive domains, visual attention and face perception. Structural imaging is performed with diffusion-weighted imaging (DWI) and fiber tractography, which track the diffusion of water molecules along white-matter fiber tracts in the brain (Figure 1). By visualizing these fiber tracts, we are able to investigate the long-range connective architecture of the brain. The results compare favorably with one of the most widely-used techniques in DWI, diffusion tensor imaging (DTI). DTI is unable to resolve complex configurations of fiber tracts, limiting its utility for constructing detailed, anatomically-informed models of brain function. In contrast, our analyses reproduce known neuroanatomy with precision and accuracy. This advantage is partly due to data acquisition procedures: while many DTI protocols measure diffusion in a small number of directions (e.g., 6 or 12), we employ a diffusion spectrum imaging (DSI)1, 2 protocol which assesses diffusion in 257 directions and at a range of magnetic gradient strengths. Moreover, DSI data allow us to use more sophisticated methods for reconstructing acquired data. In two experiments (visual attention and face perception), tractography reveals that co-active areas of the human brain are anatomically connected, supporting extant hypotheses that they form functional networks. DWI allows us to create a "circuit diagram" and reproduce it on an individual-subject basis, for the purpose of monitoring task-relevant brain activity in networks of interest.

Feasibility of Second Harmonic Imaging in Active Sonar: Measurements and Simulations

Nonlinear acoustics allows for applications like tissue harmonic imaging in medicine and parametric arrays in underwater acoustics. Mainstream sonars transmit and receive signals at the same frequency and up to now energy transferred to higher harmonic frequencies has been mainly seen as a disturbance for target strength estimation, e.g., in fishery research. This paper investigates the feasibility of utilizing the part of the signal generated around the second harmonic frequency band by nonlinear propagation of sound in water. It presents the potential enhancements the second harmonic signal may provide for target imaging as well as multifrequency target recognition. It compares measurements of the pressure field radiated by commercial transducers in water at 121 and 200 kHz up to a range of 12 m with numerical simulations. The detected levels of higher harmonic signals agree with simulations of nonlinear wave propagation. This verifies the implementation of the simulator and allows a comparison of the beam characteristics at longer ranges when filtered around the fundamental or second harmonic frequencies. An example of pulse-echo imaging with spherical targets is also shown using signals at the fundamental and second harmonic frequencies where the second harmonic signal can detect one of the targets that the fundamental signal cannot. Using the active sonar equation to estimate the maximum range, simulations based on a simple model including ambient noise and volume reverberation confirm that with a source level of 228 dB and a detection threshold of 12 dB the fundamental signal at 200 kHz can detect a fish of target strength -36 dB to approximately 343 m while the detection range of the second harmonic signal is approximately 243 m. The combined use of the signal components in the second harmonic and fundamental frequency bands provides a high-resolution image at short range and a long-range imaging capability at a lower resolution as well as a multifrequency characterization of targets.

Retroemission by a glass bead monolayer for high-sensitivity, long-range imaging of upconverting phosphors

We introduce a retroemitter (REM) device comprising a planar glass bead set placed on a luminescent material substrate, which converges an excitation beam into a set of foci (voxels). The in-voxel emission is collimated by the beads, and propagates upstream over the long range, unlike the out-of-voxel emission spreading in all angles. The REM signal contrast is characterized as a function of incidence and observation angles and propagation distance. REM signal contrasts of approximately 20 and 1600 were found for the organic fluorescent dye and upconverting phosphor substrates, respectively. In the latter case, nonlinear optical signal enhancement plays a role in addition to the retroemission effect. This allows centimeter-scale REM patterns to be read out at the meter-scale distance using eye-safe sub-mW/cm(2) excitation intensities.

Optical design of a compact long-range thermal imaging camera in the 3–5 μm wave band

In this work, the design study of a fixed focus thermal imaging system for 3–5 µm using infrared focal plane array is presented. The system is designed to have possible minimum weight and length in order to achieve the best operational characteristics. The system is designed as an objective relay combination to have 100% cold shield efficiency. In this way, the objective and relay are designed as short as possible. The objective is designed as a Schmidth–Cassegrain type mirror and the relay is a triplet type with one lens far from the others to guarantee the minimum distance to the intermediate image.

Investigations of range accuracy for long-range three-dimensional active imaging

Distance resolutions and noises are analyzed experimentally for long-range three-dimensional (3D) active imaging systems that have signal-to-noise ratios (SNRs) more optimal than 30:1. Findings indicate that the photon shot noise primarily determines the SNR. However, the active imaging method, which has a relatively low SNR, generates a relatively high distance resolution. To explain this phenomenon, a theory in which the distance resolution of 3D active imaging systems is determined by both the photon shot noise and the subinterval width is developed. Theoretical and experimental results differ by less than 4%.

Lateral collapses and active sedimentary processes on the northwestern flank of Stromboli volcano, Italy

The marine volcaniclastic system extending to 3 km water depth on the northwest flank of Stromboli volcano has been surveyed using seismo-acoustic profiling, multibeam bathymetry, deep-towed long-range side-scan sonar imaging and box-core sampling. Deposits and sea-floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present Sciara del Fuoco scar. An extensive (170 km 2) debris-avalanche deposit characterized by subdued hummocks (megablocks) is buried by turbidites formed from gravity currents that originated in Sciara del Fuoco. The currents were mainly deflected along the margin of the avalanche deposit, but also spilt over onto it. The turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows. The estimated volume of the entire fan-shaped bulge amounts to 12 ± 2.5 km 3, about 3.5 km 3 of which is attributed to the post-collapse sedimentation. The remaining 8.5 ± 2.5 km 3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the NW Stromboli flank. Two units are identified in the distal part of the bulge, through the recognition of their fronts, and these indicate a layered structure for successive debris-avalanche deposits. Granulometric and particle-type characterization of seabed samples shows clast population evolution with sedimentary transport distance, from the main entrance point of debris in Sciara del Fuoco, to the confluence with the Stromboli Canyon, and into the Marsili Basin some 45 km from the island. Changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main Stromboli Canyon from the continental shelf. Abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse-grained material along the channel to the Marsili Basin indicates that a considerable volume of volcaniclastic material from Stromboli lies in the sedimentary succession accumulating on the distal basin floor, where a deep-sea fan is growing.

Respiratory gating of anatomical optical coherence tomography images of the human airway

Anatomical optical coherence tomography (aOCT) is a long-range endoscopic imaging modality capable of quantifying size and shape of the human airway. A challenge to its in vivo application is motion artifact due to respiratory-related movement of the airway walls. This paper represents the first demonstration of respiratory gating of aOCT airway data, and introduces a novel error measure to guide appropriate parameter selection. Results indicate that at least four gates per respiratory cycle should be used, with only minor improvements as the number of gates is further increased. It is shown that respiratory gating can substantially improve the quality of aOCT images and reveal events and features that are otherwise obscured by blurring.

Don't just stand there

A long-range magnetic resonance imaging platform promises unprecedented capabilities for whole-organ visualization and high-throughput sample analysis.

Quantitative Serum Proteomics from Surface Plasmon Resonance Imaging

The detection and quantification of specific proteins in complex mixtures is a major challenge for proteomics. For example, the development of disease-related biomarker panels will require fast and efficient methods for obtaining multiparameter protein profiles. We established a high throughput, label-free method for analyzing serum using surface plasmon resonance imaging of antibody microarrays. Microarrays were fabricated using standard pin spotting on bare gold substrates, and samples were applied for binding analysis using a camera-based surface plasmon resonance system. We validated the system by measuring the concentrations of four serum proteins using part of a 792-feature microarray. Transferrin concentrations were measured to be 2.1 mg/ml in human serum and 1.2 mg/ml in murine serum, which closely matched ELISA determinations of 2.6 and 1.2 mg/ml, respectively. In agreement with expected values, human and mouse albumin levels were measured to be 24.3 and 23.6 mg/ml, respectively. The lower limits of detection for the four measurements ranged from 14 to 58 ng/ml or 175 to 755 pm. Where purified target proteins are not available for calibration, the microarrays can be used for relative protein quantification. We used the antibody microarray to compare the serum protein profiles from three liver cancer patients and three non-liver cancer patients. Hierarchical clustering of the serum protein levels clearly distinguished two distinct profiles. Thirty-nine significant protein changes were detected (p < 0.05), 10 of which have been observed previously in serum. alpha-Fetoprotein, a known liver cancer marker, was observed to increase. These results demonstrate the feasibility of this high throughput approach for both absolute and relative protein expression profiling.

Image-Quality Focusing of Rotating SAR Targets

Synthetic aperture radar (SAR) is a popular tool for long-range imaging of stationary ground objects. Moving targets in the imaged scene will have a mismatch to the matched filter in the image formation process, thus degrading target image quality. In this letter, the impact of uncompensated target rotation in SAR imagery is studied. An efficient algorithm for image-quality-based target rotation correction is proposed.

Optical turbulence parameters characterized via optical measurements over a 2.33 km free-space laser path

Optical turbulence research contributes to improved laser communications, adaptive optics, and long-range imaging systems. This paper presents experimental measurements of scintillation and focal spot displacement to obtain optical turbulence information along a near-horizontal 2.33 km free-space laser propagation path. Calculated values for the refractive index structure constant (C(n)(2)) and Fried parameter (r0) are compared to scintillometer-based measurements for several cases in winter and spring. Optical measurements were investigated using two different laser sources for the first and second parts of the experiment. Scintillation index estimates from recorded signal intensities were corrected to account for aperture averaging. As a result, we found that an earlier calculation algorithm based on analysis of log-amplitude intensity variance was the best estimator of optical turbulence parameters over the propagation path considered.

Pulse-shape-free method for long-range three-dimensional active imaging with high linear accuracy

We present a three-dimensional (3D) imaging method employing linear increasing gain to encode flying time of photons into intensity information. This method obtains both the reflectivity and the depth of scene from only two two-dimensional (2D) images. High linear accuracy between the depth and the intensity information is independent of the laser pulse shape. We demonstrated <1 m linear depth accuracies with two different kinds of laser pulse shape and a 3D scene reconstruction with supperresolution depth mapping when the targets are 800-1100 m away.

Long-range three-dimensional active imaging with superresolution depth mapping

We present a technique to overcome the depth resolution limitation for 3D active imaging. Applying microsecond laser pulses and sensor gate width, a scene of several hundred meters is illuminated and recorded in a single image. The trapezoid-shaped range intensity profile is analyzed to obtain both the reflectivity and the depth of scene. We demonstrate a 3D scene reconstruction in a depth of 650 to 1550 m from only three images with an accuracy of <30 m. This depth accuracy is 10 times better than estimated from the classical resolution limit obtained for depth scanning active imaging with a similar number of images. Therefore, this technique enables superresolution depth mapping with a reduction of image data processing.

Degrading effects of the lower atmosphere on long-range airborne synthetic aperture radar imaging

The imaging performance of airborne synthetic aperture radar (SAR) systems has advanced to the point that the effects of clear-air refractive index perturbations cannot be ignored. Operating at long ranges, and low grazing angles, in particular, require propagation geometries through regions of the lower atmosphere that may cause noticeable and, sometimes, severe degradation of the images. The range of image anomalies that can be attributed to the atmospheric boundary layer (ABL) is illustrated, the pertinent characteristics of the ABL is discussed, a first-order SAR imaging model that incorporates the refractive index perturbations associated with the ABL is developed and the magnitude of the image anomalies resulting from measured refractive index perturbations is estimated. The model predictions correlate well with the observed image anomalies and measured properties of the ABL. On the basis of theory and measurements, it is expected that the degrading effect of clear-air atmospheric refractive index perturbations is much more common than previously thought and may be a limiting factor for long-range SAR imaging performance.

Turbulence strength estimation from an arbitrary set of atmospherically degraded images

In remote sensing, atmospheric turbulence and aerosols usually limit the image quality. For many practical cases, turbulence is shown to be dominant, especially for horizontal close-to-earth imaging in hot environments. In a horizontal long-range imaging, it is usually impractical to calculate path-averaged refractive index structure constant C(2)(n) (which characterizes the turbulence strength) with conventional equipment. We propose a method for estimating C(2)(n) from the available atmospherically degraded video sequence by calculating temporal intensity fluctuations in spatially high variance areas. Experimental comparison with C(2)(n) measurements using a scintillometer shows reliable estimation results.

Long-range three-dimensional imaging using range-gated laser radar images

An approach to long-range 3-D imaging using laser illuminated range-gated viewing is presented. The basis for 3-D scene reconstruction is an image sequence acquired using a sliding gate delay time. Two different methods are suggested, and algorithm performance is investigated through Monte Carlo simulations using a simplified system and imaging model. Assumptions are justified by comparison with real measurements at range of 0.8 to 7.2 km. It is shown that range resolution and precision become significantly better than system design parameters such as gate length, gate transition length, and gate step length. The presented reconstruction methods thus enable high-precision range imaging using available long-range gated imaging systems.

PAMIR – a wideband phased array SAR∕MTI system

Air- and spaceborne imaging radar systems in forthcoming surveillance and reconnaissance tasks have to meet increasingly severe demands. The next generation of top-level synthetic aperture radar (SAR) systems will comprise, among others, high resolution and long-range imaging capabilities, highly sensitive ground moving target indication and a multitude of sophisticated operational modes. The variety of tasks can be fulfilled only by the use of a reconfigurable phased array antenna together with a comprehensive wideband system design and a multichannel capability. At FGAN a new experimental X-band radar has been conceived, which will possess in its final upgrade an electronically steerable phased array consisting of 16 autonomous and reconfigurable subapertures, five independent receive channels, and a total signal bandwidth of about 1.8 GHz. The sensor is called PAMIR (Phased Array Multifunctional Imaging Radar). It is envisaged to demonstrate SAR imaging at a very high resolution and for a long range. The fine resolution will also be achieved with inverse SAR (ISAR) imaging of ground moving objects. Furthermore, the number of receive channels will allow ground-moving target indication (GMTI) by space–time adaptive processing and single-pass interferometric SAR (IfSAR) with a very high 3-D resolution. In its current stage of extension PAMIR is operable with one receive channel and a mechanically steerable antenna array. The system design and the intended capabilities of PAMIR are described. Ground-based and airborne experimental results concerning high-resolution SAR and ISAR imaging are also presented.

Update: a protein microbolometer for focal plane arrays

The current infrared microbolometer technology using vanadium oxide material is not quite as sensitive as a cooled platinum silicide or cooled mercury cadmium telluride or indium antimonide array. The performance factor of the present IR bolometer needs to be improved by at least an order of magnitude to make a bolometric IR device comparable to the cooled detector arrays. I recently reported [1] that thin films of globular proteins such as cytochrome c exhibit a high temperature coefficient of resistance (TCR) value of about 10% as compared with a value of 2.0 to 2.5% normally observed in VOx films. The measurements that were initially reported were taken two weeks after the thin films had been prepared. The measurement of the TCR values presented in this report were taken within three days of the films being prepared. These TCR values are very high, approximately 35% for temperatures between 25 and 60°C, and they have a sheet resistance around 1 to 2 Ω/cm2 with a current of 1 mA. The values of TCR were very uniform over the wafer surface, but the values varied slightly from wafer to wafer. It appears that a cytochrome c monolayer on metal oxide semiconductor (CMOS) electronics could generate miniaturized, uncooled IR detector arrays that would be suitable for military and commercial applications that require very high performance and low-power drain. With these high TCR values, biological uncooled devices will have the potential for long-range thermal imaging applications comparable to cooled detectors.I have also examined the sheet resistance of the protein layer with an increase in the bias current near ambient temperature. I found that the sheet resistance of cytochrome c rapidly goes towards the negative values as the bias current is increased. On the other hand, TCR characteristics remained unchanged with an increase in bias current. This is a very interesting phenomenon that has never been reported in biomolecules. I am making further explorations into the electrical properties of many proteins for possible device applications.

Super high resolution for long-range imaging

A new optical system with a resolution that is superior to the resolution of the usual optical systems with diffraction limit is presented. We introduce a newly generated narrow light beam that propagates for a long range while almost maintaining its beam width and show that the beam width is narrower than that of the diffraction limit of normal optics. Thus a super high resolution is achieved for a long range, e.g., a range of a few kilometers, by the use of a 10-cm-diameter telescope. The high resolution for long-range imaging can be obtained by a Galilean telescope with a negative eyepiece that has a spherical aberration. We demonstrate theoretically high-resolution imaging by using simple objects and assuming a telescope 10 cm in diameter and a visible wavelength. A comparison of simulation results by the conventional optical system and by the special optical system clearly shows the superiority of the new system.

SAMI: a low-frequency prototype for mapping and imaging of the seabed by means of synthetic aperture

The objective of the Synthetic Aperture Mapping and Imaging (SAMI) project was to develop and to test at sea a wide-band synthetic aperture sonar prototype, capable of providing high-resolution seafloor images together with bathymetry maps. This system used the motion of a physically small array in order to synthesize a longer array, providing images with an across-track resolution independent of both range and transmit frequency. Such systems are clearly very relevant to the high-precision long-range (low-frequency) imaging of the sea bottom. The project has led to the construction of a prototype tested at sea on several well-known areas for comparison with existing images and maps. These areas included several types of sea bottom, depths, and geological structures. The results obtained in real time, on-board ship, have shown the relevance of the proposed wide-band techniques. The many profiles produced have provided high-resolution images and maps of various seafloors. Interpretation by geologists showed that the system was capable of providing the same or finer detail than a deep-sea short-range, high-frequency system and maintained a higher resolution over a wider swath. The sea data processed have shown that the system provided maps with a cubic meter voxel. The resolution cell is constant over the whole range (50 to 2500 m) thanks to the dynamic focusing of the synthetic aperture. Postprocessing of a part of the data stored during the experiments has been carried out in the laboratory. This work has shown that techniques such as autofocusing can give an increase in resolution (i.e., gain in contrast and resolution of about 3 dB). The results displayed in the paper show the relevance of the techniques developed to the provision of a complete high-performance imaging tool for the oceanographic community.