Two-dimensional X-ray Images Research Articles

Analysis of trabecular bone texture by modified Hurst orientation transform method.

There is a growing need for noninvasive and inexpensive methods that can effectively be used on a large scale, to detect an onset of early osteoarthritis in human knee joints. Of many possible options, fractal analysis of two-dimensional projection x-ray images of trabecular bone (TB) texture, appears as one of the best approaches. However, there are some problems associated with the characterization of the roughness and anisotropy of the bone texture. To resolve these problems, a modified Hurst orientation transform (HOT) method, previously developed by the authors, has been used in this study. The advantages of the HOT method over other techniques used to analyze bone texture, are that it calculates a two-dimensional fractal dimension in all possible directions and also provides a measure of anisotropy for both surfaces exhibiting strong anisotropy and surfaces exhibiting weak anisotropy. In this study, the accuracy of the HOT method in measuring the bone texture roughness and anisotropy; together with the effects of image noise, blur, exposure, magnification, and projection angle on its performance were investigated. Computer-generated images of fractal surfaces and x-ray images obtained for a human tibia head were used. Results obtained show that the HOT method can effectively be used to characterize the roughness and anisotropy (isotropy) of TB texture.

Microsecond time-resolved 2D X-ray imaging

A method is presented which allows to take two-dimensional X-ray images of repetitive processes with recording times in the sub-microsecond range. Various measurements have been performed with a recently introduced novel two-dimensional single photon counter which has been slightly modified in order to determine the exact arrival time of each detected photon. For this purpose a special clock signal is synchronized with the process and is digitized contemporaneously with each event. This technique can be applied even with rate limited detectors and low flux sources, since—unlike in conventional methods, where chopped beams or gated read out electronics are used—all photons are used for the image formation. For the measurements, rapidly moving mechanical systems and conventional X-ray sources have been used, reaching time resolutions of some 10 μs. The technique presented here opens a variety of new biological, medical and industrial applications which will be discussed. As a first application example, three dimensional tomographic reconstructions of rapidly rotating objects (4000 turns/min) are presented.

Development of wide-field, multi-imaging x-ray streak camera technique with increased image-sampling arrays

In order to enlarge the field of view of a multi-imaging x-ray streak (MIXS) camera technique [H. Shiraga et al., Rev. Sci. Instrum. 66, 722 (1995)], which provides two-dimensionally space-resolved x-ray imaging with a high temporal resolution of ∼10 ps, we have proposed and designed a wide-field MIXS (W-MIXS) by increasing the number of image-sampling arrays. In this method, multiple cathode slits were used on the photocathode of an x-ray streak camera. The field of view of the W-MIXS can be enlarged up to 150–200 μm instead of ∼70 μm for a typical MIXS with a spatial resolution of ∼15 μm. A proof-of-principle experiment with the W-MIXS was carried out at the Gekko-XII laser system. A cross-wire target was irradiated by four beams of the Gekko-XII laser. The data streaked with the W-MIXS system were reconstructed as a series of time-resolved, two-dimensional x-ray images. The W-MIXS system has been established as an improved two-dimensionally space-resolved and sequentially time-resolved technique.

Calibration of High-Resolution X-Ray Tomography With Atomic Force Microscopy.

For two-dimensional x-ray imaging of thin films, the technique of scanning transmission x-ray microscopy (STXM) has achieved images with feature sizes as small as 40 nm in recent years. However, calibration of three-dimensional tomographic images that are produced with STXM data at this scale has not yet been described in the scientific literature, and the calibration procedure has novel problems that have not been encountered by x-ray tomography carried out at a larger scale. In x-ray microtomography, for example, one always has the option of using optical imaging on a section of the object to verify the x-ray projection measurements; with STXM, on the other hand, the sample features are too small to be resolved by light at optical wavelengths. This fact implies that one must rely on procedures with higher resolution, such as atomic force microscopy (AFM), for the calibration. Such procedures, however, generally depend on a highly destructive sectioning of the sample, and are difficult to interpret because they give surface information rather than depth information. In this article, a procedure for calibration is described that overcomes these limitations and achieves a calibration of an STXM tomography image with an AFM image and a scanning electron microscopy image of the same object.A Ge star-shaped pattern was imaged at a synchrotron with a scanning transmission x-ray microscope. Nineteen high-resolution projection images of 200 × 200 pixels were tomographically reconstructed into a three-dimensional image. Features in two-dimensional images as small as 40 nm and features as small as 80 nm in the three-dimensional reconstruction were resolved. Transverse length scales based on atomic force microscopy, scanning electron microscopy, x-ray transmission and tomographic reconstruction agreed to within 10 nm. Toward the center of the sample, the pattern thickness calculated from projection images was (51 ± 15) nm vs (80 ± 52) nm for tomographic reconstruction, where the uncertainties are evaluated at the level of two standard deviations.

Excimer laser processing for a-Si and poly-Si thin film transistors for imager applications

Pulsed excimer laser annealing (ELA) has become an important technology by which to produce high performance thin film transistors (TFTs) for large area electronics. The applications of these advanced TFTs in flat-panel displays and flat-panel imagers for two-dimensional x-ray imaging have attracted much interest. TFTs made from excimer laser crystallized poly-Si thin films with mobilities higher than 100 cm2/V s and off-state leakage currents lower than 2 fA/μm at drain voltage VD=5 V have recently been achieved. The improved off-state leakage current enables one to consider making flat-panel imagers based on poly-Si TFT technology. Laser doping or dopant activation is another important application of the ELA process. Using a laser doping process, we have fabricated a-Si TFTs with self-aligned poly-Si source/drain contacts. These new devices have reduced source/drain parasitic capacitance and their channel length can easily be scaled down. In this article, we will review the excimer laser processing technology for both the poly-Si TFT technology and self-aligned a-Si:H TFT technology and report the current status of developing flat-panel imagers using these new TFT technologies.

An X-ray photon-counting imaging spectrometer based on a Ta absorber with four superconducting tunnel junctions

We present the first results obtained with a two-dimensional X-ray imaging spectrometer consisting of a 200×200 μm 2 Ta absorber and read out by four Ta/Al superconducting tunnel junctions (STJs). A preliminary image reconstruction algorithm allows the visualisation of the diffraction pattern from a 5 μm pinhole illuminated with 10 keV X-rays. The image suggests a spatial resolution better than 10 μm. The algorithm does not take into account quasi-particle losses in the absorber. Hence, the pulse-height reconstruction is not optimal and the energy resolution varies significantly across the absorber. The best energy resolution is obtained for a 20×20 μm 2 area in the centre of the absorber, and amounts to ∼77 eV at a photon energy of 5895 eV, with a 70 eV electronic noise contribution.

APPLE WATERCORE SORTING SYSTEM USING X-RAY IMAGERY: I. ALGORITHM DEVELOPMENT

Watercore is an internal disorder that leads to breakdown of tissue and possibly loss or downgrade of theproduct. It is very difficult to determine whether an apple contains watercore or not, especially in the early stages, basedsolely on external information, since watercore does not alter external texture until after severe internal breakdown. Inthis study, we explored the possibility of using two-dimensional (2-D) X-ray imaging to detect internal watercore damagein apples. The algorithm to detect Red Delicious watercore apples consists of two stages, the first stage extracts featuresfrom the apple x-ray image and the second stage categorizes apples into different watercore levels using the featuresidentified. A total of eight features were extracted from an x-ray scanned apple image and these features were fed intoneural network classifier to categorize them into three different classes, clean, mild, and severe. The results showed thatthe system was able to correctly recognize apples into clean and severe categories within 5-8% false positive and negativeratios. The result also showed that the algorithm was able to recognize apples independent of apple orientation, but onlyif the stem-calyx axis made a fixed angle with the x-ray beam. Sorting at random apple orientation was not tested. Theestimated speed of the system, if implemented on a DSP board, will be fast enough to keep up with the current appleprocessing line.

A three-dimensional CT (CAT) scan through a rock with Permian alga Ivanovia tebagaensis

Embedded thalli of Permian Ivanovia tebagaensis, a calcified, cyathiform, codiacean, Chlorophyta, were X-rayed with a medical CT (computed tomography) scanner. The two-dimensional digital X-ray image files were copied to floppy disks and transferred to an IBM-compatible personal computer. The images were cropped, and built into a data volume with a commercial three-dimensional software program. The data were color edited so that only the algae were visible. The data volume was then systematically manipulated to visualize some hitherto unknown details of the structure of the utricles, and of a vegetative propagule, a developing bud.

Two-dimensional sampling-image x-ray streak camera for ultrafast imaging of inertial confinement fusion plasmas

Ultrafast two-dimensional (2D) x-ray imaging with a temporal resolution better than 10 ps is of great importance in diagnosing the final stages of the imploded core plasmas of inertial confinement fusion (ICF) targets. The multi-imaging x-ray streak camera (MIXS) has been one of such imaging techniques. Recently, we have proposed another scheme, a 2D sampling-image x-ray streak camera method (2D-SIXS). In this scheme, a 2D image is sampled two dimensionally with a set of sampling points distributed regularly over the whole image on a cathode plate of an x-ray streak camera. The sampled image is streaked, and then, reconstructed to form the time-resolved 2D images like movie pictures. In this article, we report results of our proof-of-principle experiments of 2D-SIXS scheme performed at Gekko-XII glass laser system. A gold-coated spherical target was irradiated by three beams (0.53 μm) of Gekko-XII laser. Streaked data of 2D-SIXS were obtained and a series of time-resolved 2D x-ray images were successfully reconstructed. 2D-SIXS is suitable for very fast, short-lived, and small x-ray sources such as a hot spark in the ICF plasma as well as short-pulse-laser-produced plasmas.

Characterization of a prototype pixel array detector (PAD) for use in microsecond framing time-resolved X-ray diffraction studies

A 4 by 4 pixel array device has been designed and built as a prototype for a high-speed two-dimensional X-ray imaging detector. This detector is a two-tier device with an X-ray sensitive photo-diode array bump-bonded to a 1.2 micrometer CMOS analog integrated circuit. Each 150 micrometer square pixel of the detective layer is matched to a corresponding section of the electronics. Each pixel of the electronics is capable of integrating the signal from the diode for the desired framing time, storing the result in one of eight storage capacitors and sequentially outputting the stored value to an on chip buffering op amp. Tests of the electronics have demonstrated a full-well (per pixel, per frame) of over 10.500 12 keV X-rays with an electronics noise level corresponding to less than 2.8 12 keV X-rays. Speed tests indicate the ability to integrate to the full-well within 2 microseconds (an average pixel count-rate of 5.2 GHz). We present detailed characterizations of the performance of this initial device, including an analysis of noise, stability, linearity and point spread. In addition, we will discuss plans for large scale integration towards the goal of a 1024 by 1024 pixel detector.

New method for comprehensive phase-amplitude contrast imaging of the internal structure of matter using high-energy radiation

A nondestructive method for structural imaging is proposed. The method is based on direct measurements of phase and amplitude changes in a two-dimensional x-ray image. A standing wave is formed between two separated crystals allowing high-resolution imaging of the complex refractive index. A comprehensive analysis of the amplitude-phase contrast is possible because of the precisely controlled variation of the phases between the reference and reflected beams from a crystalline mirror.

Two-dimensional imaging X-ray spectrometer for plasma diagnostics

A two-dimensional imaging soft X-ray monochromator is now under development. The main components of this spectrometer are a channel plate collimator (CPC) and multilayer mirrors. We have applied this monochromator to obtain soft X-ray images of GAMMAIO tandem mirror plasmas. In order to obtain clear images in a low energy X-ray regime, we have utilized and tested a focusing effect of the CPC. Ray-trace simulations were carried out under the same conditions as the experiments. After comparison of these results, we have confirmed that the focusing effect of the CPC is useful in practical use. Monochromatized two-dimensional soft X-ray images have been successfully taken on the tandem mirror experiment.

One- and two-dimensional fast x-ray imaging of laser-driven implosion dynamics with x-ray streak cameras

One- (1D) and two-dimensional (2D) x-ray imaging techniques with x-ray streak cameras have been developed and utilized for investigating implosion dynamics of laser fusion targets. Conventional streaked 1D images of the shell motion of the imploding target was recorded together with the time-resolved 2D multi-imaging x-ray streak images of the core shapes on the same x-ray streak camera. Precise comparison of the core dynamics between the experimental and simulation results was performed with an accuracy of 30 ps by fitting the trajectories of the x-ray emission from the imploding shell.

Ultrafast two-dimensional x-ray imaging with x-ray streak cameras for laser fusion research (invited)

Ultrafast two-dimensional x-ray imaging is required for diagnosing laser-driven inertial confinement fusion plasmas. Image sampling technique with x-ray streak cameras can meet this requirement. Multi-imaging x-ray streak camera method (MIXS) with temporal and spatial resolutions of 10 ps and 15 μm, respectively, has been developed and successfully utilized for diagnosing the uniformity and heating process of the imploded core plasmas. The two-dimensional sampling-image x-ray streak camera method is also presented. Two types of spectroscopic applications of the MIXS have been developed recently. One is multichannel MIXS, which has three MIXS channels with various spectral responses for time-resolved two-dimensional temperature measurement of the plasmas. Another is monochromatic MIXS for temperature, density, and mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS.

Eu concentration dependence of photostimulated luminescence in X-ray or UV-ray irradiated KCl: Eu phosphor ceramics

Europium doped potassium chloride (KCl:Eu) phosphor ceramics for two-dimensional X-ray or UV-ray imaging sensor utilizing photostimulated luminescence phenomenon (PSL) were prepared. Investigation of Eu concentration dependence of the PSL in X-ray or UV-ray irradiated KCl:Eu phosphor ceramics was carried out. An intense PSL with a peak at about 420 nm was observed in 0.5 mol % Eu doped KCl phosphor ceramics which is fabricated by sintering at about 700°C in air.

Photostimulated luminescence in CaS: Eu,Sm phosphor ceramics induced by excitation with ionizing radiation

Intense photostimulated luminescence (PSL) with a peak at about 650 nm is observed in europium and samarium co-doped calcium sulfide (CaS: Eu,Sm) phosphor ceramics by excitation with ionizing radiation such as X-rays and UV-rays. The PSL intensity is increased by increasing the X-ray or UV-ray dose, indicating that CaS: Eu,Sm phosphor is a useful material for two-dimensional X-ray or UV-ray imaging sensor utilizing PSL. The results obtained are consistent with the proposed emission mechanism of the 650 nm PSL, based on the recombination of electrons released from Sm 2+ ions as electron traps with Eu 3+ ions.

High-energy radiation visualizer (HERV): a new system for imaging in X-ray and gamma-ray emission regions

We present a description and results of the operation for /spl gamma/-ray and X-ray objects for the compact visualization system high-energy radiation visualizer (HERV). The imaging in this system is based on use of a conical collimator, scintillator plate, and image intensifier as a detector and CCD matrix as a readout device. The use of HERV as a two-dimensional X-ray image visualizer for the Compton scatter inspection system was considered and first results are discussed. The possibility of using different hexagonal-coded apertures imaging for HERV is discussed and results of Monte Carlo simulation and experiments with optical analog of coded aperture are presented.

Comparison of film, direct digital, and tuned-aperture computed tomography images to identify the location of crestal defects around endosseous titanium implants

This study compared diagnostic performance obtained from two-dimensional and three-dimensional x-ray images. The latter were produced with a new tomosynthetic method based on aperture theory called tuned-aperture computed tomography. Seven human cadaver mandibular segments containing a total of 20 endosseous implants with a small randomly positioned alveolar crestal defect at each implant site were imaged in two dimensions with periapical film and with a charge-coupled digital detector, and digitally with the same detector in three dimensions with tuned-aperture computed tomography and subtracted tuned-aperture computed tomography techniques. Seven trained dentists viewed randomized displays of all modalities. Outcomes of the diagnostic task of identifying the locations of crestal defects were quantified with accuracy, confidence, and time performance measures. Analyses of variance demonstrated that differences between either three-dimensional technique and either two-dimensional modality were significant for all measures (p < 0.001). These findings suggest that clinically applied TACT methods hold promise as an improvement over the status quo.

Fast electron transport and lower hybrid absorbed power profiles from hard x-ray imaging in the Princeton Beta Experiment-Modified

Recent hardware improvements on the hard x-ray camera of the Princeton Beta Experiment-Modified (PBX-M) expand the capabilities for observing bremsstrahlung radiation from fast electrons during lower hybrid current drive (LHCD) experiments, thereby allowing accurate fast electron transport studies. Developed methods to directly invert two-dimensional x-ray images reveal radial profiles of the emitted intensity and isotropy. Such profiles extracted from lower hybrid (LH) modulation experiments permit computation of the lower hybrid power absorption profile. Results from application to the LH phase scans demonstrate the ability to control the peak location of the driven current. Incorporating these results into simulations using both a three-dimensional Fokker–Planck code and a simple modulation model provides lower and upper bound estimates for the hot electron diffusion coefficient D*.

Laser-imploded core structure observed by using two-dimensional x-ray imaging with 10-ps temporal resolution

Core plasmas of laser-imploded ICF targets were observed by using a 10-ps temporally resolved two-dimensional x-ray imaging technique. A multi-imaging x-ray pinhole camera was coupled to an x-ray streak camera, and two-dimensional images were reconstructed by handling the streaked image data. Image distortion of the system was evaluated and nonuniformity in sensitivity was corrected. The spatial resolution was 15 μm and the observed photon energy was 2.2–4.9 keV. Structures in the x-ray image of the core were found to be rapidly changing with 10-ps time scale.