Search

X-ray phase-contrast imaging is a potential nondestructive testing and diagnostic technology in medicine, biology and materials science. It provides high sensitivity and contrast of weakly absorbing Iow-Z objects by measuring phase shifts of the X-rays. In this paper, we propose a novel phase-contrast imaging method using only one absorption grating and a high-resolution detector. The intensity distribution downstream of the grating is recorded and analyzed by the high-resolution detector directly. We use a spatial phase demodulation method to retrieve the phase information. Only one image is needed. Numerical simulations are performed to validate that the setup of our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming and the unnecessary dose. Index Terms--Phase contrast, phase measurement, spatial phase demodulation, X-ray imaging.

We present a new algorithm which merges discontinuities in 3-D images of tubular structures presenting undesirable gaps. The application of the proposed method is mainly associated to large 3-D images of microvascular networks. In order to recover the real network topology, we need to fill the gaps between the closest discontinuous vessels. The algorithm presented in this paper aims at achieving this goal. This algorithm is based on the skeletonization of the segmented network followed by a tensor voting method. It permits to merge the most common kinds of discontinuities found in microvascular networks. It is robust, easy to use, and relatively fast. The microvascular network images were obtained using synchrotron tomography imaging at the European Synchrotron Radiation Facility. These images exhibit samples of intracortical networks. Representative results are illustrated. Index Terms--Gap filling, skeleton, tensor voting, vessel extraction, X-ray imaging.

The dynamic lateral polarization and charge steering effect was studied in 2D pixilated CdZnTe monolithic detector arrays designed for high flux x-ray imaging applications. While these detectors have shown the ability to work at 15 x [10.sup.6] counts/s/[mm.sup.2] and higher count-rates in pulse mode, we observed some detectors that exhibited a dynamic lateral polarization and charge steering effect causing non-uniform spatial response to the radiation field. The dynamic nature of the effect is shown by its flux dependence and reversibility upon changing the x-ray flux without a requirement to turn off the bias voltage. The effect causes the induced charge that would normally move from the cathode towards the anode to instead move laterally causing counts to shift away from a flux boundary. We show that the effect is not related to the physical boundary of the detector but rather related to the boundary of the irradiated area of the device. The dynamic polarization and charge steering effect can be attributed to the limited hole transport in the bulk material causing a buildup of a dynamic space-charge region under the irradiated area. The resulting lateral (perpendicular to the irradiation direction) electric field causes the lateral drift (steering) of the x-ray injected charge clouds. The static version of such lateral steering is often observed for charged structural defects in CdZnTe crystals. The studied 2D CdZnTe monolithic arrays were 16 x 16pixel devices having 0.4 mm x 0.4 mm area pixels on a 0.5 mm pitch and were fabricated using 8.7 mm x 8.7 mm x 3.0 mm CdZnTe single crystals grown by the high-pressure electro-dynamic gradient freeze technique. The devices were probe tested in a system consisting of a custom 16 x 16 pin probe head, 256 channel read-out electronics utilizing 8-channel fast bipolar ASIC chips, and a computer controlled 120 kVp x-ray source. Index Terms--CdZnTe, polarization, semiconductor radiation detectors, x-ray detectors, x-ray imaging.

We report here on self-magnetic-pinch diode experiments at voltages from 3.5 to 6 MV. In addition to electrical diagnostics, the diode is characterized as a radiation source by dose and spot-size measurement. As the operating voltage increases, we find that a given diode geometry tends to produce a smaller spot but suffers from the reduced impedance lifetime. Optimization involves increasing the cathode diameter and diode gap as the voltage increases. We find a good quantitative agreement with the Monte Carlo code integrated tiger series over the entire data set, assuming an effective electron incidence angle of 20[degrees]. Over this range, we observe favorable dose and spot scaling of optimized diode performance with voltage. Our best results are roughly 200-rad CaF2 at 1 m with an ~2-mm-diameter spot. These were obtained at diode parameters of roughly 6 MV, 150 kA, and 30-ns radiation full-width at half-maximum. Index Terms--Electron beams, particle beams, pinched-beam diodes, pulsed power, radiography.

The luminescence of [(Lu, Y).sub.2]Si[O.sub.5]: Ce (LYSO:Ce) and [Gd.sub.2]Si[O.sub.5]: Ce (GSO:Ce) crystals was studied for use in tomographic medical x-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/[cm.sup.3] and 6.71 g/[cm.sup.3] respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. Evaluation was performed by determining: 1) the luminescence efficiency (LE) (emitted fight energy flux over incident x-ray energy flux) in x-ray energies employed in general x-ray imaging (40-140 kVp) and in mammographic x-ray imaging (22-49 kVp), 2) the fight emission spectrum, determined at various x-ray energies (22-140 kVp), and 3) the spectral compatibility to optical photon detectors, incorporated in medical imaging systems. Both scintillation materials exhibited adequately high LE in the x-ray diagnostic energy range, with LYSO:Ce's LE being distinctively higher. LYSO:Ce and GSO:Ce were found most compatible with the S-20 photocathode (0.9 for both materials) and adequately compatible to the amorphous silicon photodiode (0.74 for both materials), incorporated in many digital x-ray detectors. Index Terms--Inorganic scintillators, luminescence efficiency, LYSO:Ce, matching factor, radiation detectors.

This work describes an investigation on the use of polymeric blends as the host material in flexible thermoluminescent (TL) films, for application in digital radiography. Polymeric films made of semi-crystalline poly(vinylidene fluoride--trifluorethylene) [P(VDF-TrFE)] copolymer blended with 0, 5, 10, 15, 25, 30, and 35% wt. of amorphous poly(methyl methacrylate) [PMMA] were studied using Differential Scanning Calorimetry (DSC) and UV-VIS spectrometry. Combining data from blend compatibility and melting temperature of the crystallites, we found out that the P(VDF-TrFE)/PMMA with contents of PMMA until 15% wt. can be used for hosting thermoluminescent materials. Above this value, there is no more compatibility between these materials, with the appearance of small clusters of PMMA. Among the candidates, the blend with 15% wt. shows the best optical transparence and thus it has been chosen as the optimal blend composition for use as host matrix in a TL film, once the thermoluminescent visible light emitted from the granules localized beneath the film surface has a higher probability of getting outside, without optical scattering. Digital radiographic images emitted from heated films made of CaS[O.sub.4]:Mn storage phosphor powder dispersed into these blends were captured using a standard charged coupled device (CCD). The quality of the obtained radiographic images shows that TL plastic films present high potential to be an alternative way to obtain digital images, commonly obtained by photoluminescence based devices or X ray sensitive CCD cameras. Index Terms--Radiation detectors, thermoluminescence, digital imaging, plastic films, radiography, P(VDF-TrFE) copolymers, P(VDF-TrFE)/PMMA blends.

Mercuric iodide films were grown by the physical vapor deposition method on palladium-coated glass substrates 2' x 2' in size. The growth was performed in a system especially designed and constructed for getting a fine control of the growth parameters. The best growth conditions were a source temperature of 120 [degrees]C, a growth temperature of 60 [degrees]C and a growth time of 24 h, with an initial pressure of 6 x [10.sup.-3] Pa. Film thicknesses and grain sizes gave values ranging between 100 and 260 [micro]m (10%), and between (10 [+ or -] 5) and (30 [+ or -] 10) [micro]m, respectively. Films grew oriented with the (0 0 l) crystalline planes parallel to the substrate, with a texture of 0.94, measured by X-ray powder diffraction. The dark current density of the films is lower than 0.3 pA/[mm.sup.2] for electric fields below 0.4 V/[micro]m, and their resistivity is 1.5 x [10.sup.14] [ohm].cm. Mobility-lifetime values of 5.2 x [10.sup.-6] [cm.sup.2]/V and 6.2 x [10.sup.-6] cm2/V can be estimated for electrons and holes, respectively. Films give a sensitivity to X-rays of 37 nC/R.[cm.sup.2]. A signal to dark relation of 1120 was measured at 750 mR/s and 32 KVp, with an electric field of 0.4 V/[micro]m applied to the film. The low dark current, as far as the high signal to noise results obtained, indicate these films as very suitable for direct and digital imaging. Index Terms--Digital radiography, mercuric iodide, oriented films.

Generation of digitally reconstructed radiographs (DRRs) is computationally expensive and is typically the rate-limiting step in the execution time of intensity-based two-dimensional to three-dimensional (2D-3D) registration algorithms. We address this computational issue by extending the technique of light field rendering from the computer graphics community. The extension of light fields, which we call attenuation fields (AFs), allows most of the DRR computation to be performed in a preprocessing step; after this precomputation step, DRRs can be generated substantially faster than with conventional ray casting. We derive expressions for the physical sizes of the two planes of an AF necessary to generate DRRs for a given X-ray camera geometry and all possible object motion within a specified range. Because an AF is a ray-based data structure, it is substantially more memory efficient than a huge table of precomputed DRRs because it eliminates the redundancy of replicated rays. Nonetheless, an AF can require substantial memory, which we address by compressing it using vector quantization. We compare DRRs generated using AFs (AF-DRRs) to those generated using ray casting (RC-DRRs) for a typical C-arm geometry and computed tomography images of several anatomic regions. They are quantitatively very similar: the median peak signal-to-noise ratio of AF-DRRs versus RC-DRRs is greater than 43 dB in all cases. We perform intensity-based 2D-3D registration using AF-DRRs and RC-DRRs and evaluate registration accuracy using gold-standard clinical spine image data from four patients. The registration accuracy and robustness of the two methods is virtually identical whereas the execution speed using AF-DRRs is an order of magnitude faster. Index Terms--Digitally reconstructed radiographs, image-guided therapy, intensity-based 2D-3D image registration, light fields.

We compared the detection characteristics of a pixel area X-ray detector, Medipix-2, with those of a CCD-based X-ray detector. The goal was to challenge the overall imaging performance of the emerging pixel area detection technique against that of a well-known detection device, in view of applications on synchrotron beamlines. A CCD-based detector was chosen as the reference because of the intensive and widespread use of CCD systems on beamlines. In order to establish the comparison on an absolute side-by-side basis we built an optimized CCD-based system with the same input pixel size as Medipix-2 and we characterized both systems in identical conditions. We present the results obtained, in particular the frequency-dependent noise, spatial response and DQE. We also report on various test experiments with Medipix-2 in X-ray scattering and X-ray imaging using a synchrotron source. Index Terms--DQE, MTF, pixel detectors, SAXS, synchrotron, X-ray imaging.

In this paper, we present an original method for the three-dimensional (3-D) reconstruction of the scoliotic rib cage from a planar and a conventional pair of calibrated radiographic images (postero-anterior with normal incidence and lateral). To this end, we first present a robust method for estimating the model parameters in a mixture of probabilistic principal component analyzers (PPCA). This method is based on the stochastic expectation maximization (SEM) algorithm. Parameters of this mixture model are used to constrain the 3-D biplanar reconstruction problem of scoliotic rib cage. More precisely, the proposed PPCA mixture model is exploited for dimensionality reduction and to obtain a set of probabilistic prior models associated with each detected class of pathological deformations observed on a representative training scoliotic rib cage population. By using an appropriate likelihood, for each considered class-conditional prior model, the proposed 3-D reconstruction is stated as an energy function minimization problem, which is solved with an exploration/selection algorithm. The optimal 3-D reconstruction then corresponds to the class of deformation and parameters leading to the minimal energy. This 3-D method of reconstruction has been successfully tested and validated on a database of 20 pairs of biplanar radiographic images of scoliotic patients, yielding very promising results. As an alternative to computed tomography-scan 3-D reconstruction this scheme has the advantage of low radiation for the patient, and may also be used for diagnosis and evaluation of deformity of a scoliotic rib cage. The proposed method remains sufficiently general to be applied to other reconstruction problems for which a database of objects to be reconstructed is available (with two or more radiographic views). Index Terms--Biplanar radiographies, medical imaging, mixtures of probabilistic principal component analyzers, reduction of dimensionality, scoliosis, shape model, stochastic optimization, 3-D reconstruction model, 3-D/2-D registration.

An image acquisition system is presented for use with position sensitive detectors (PSD). The system is based on a high-resolution time-to-digital converter (TDC) and a field programmable gate array (FPGA). The detectors use gas as absorbing medium and two delay lines to identify the coordinates of each detected particle. The TDC translates the time information coming from the delay lines into digital words, from which the particle position coordinates are encoded. The FPGA is responsible for processing each event, controlling the data acquisition and communicating with a personal computer. 256 pixels x 256 pixels images are stored into an on-board memory. This resolution is increased to 512 pixels x 512 pixels by using a time multiplexing technique. The maximum data acquisition rate is 1.2 million events per second. X-ray images obtained with the system are shown, which illustrate the overall performance. Index Terms--Delay line readout, image acquisition system, time-to-digital converter, X-ray detector.

Self-magnetic-pinched diode behavior at 1.5-2 MV was diagnosed using a variety of electrical, radiation, and optical diagnostics. Results are compared with predictions of the LSP particle-in-cell code, and shown to be in good agreement. A practical diagnostic of electron incidence angles is demonstrated. A quadrature interferometer is shown to be capable of measuring the time-dependent position of the effective electrode-plasma boundaries. Both one-dimensional (1-D) and two-dimensional (2-D) interferometry show the importance of anode plasma expansion in such diodes with high anode-power concentration. Not only does the anode plasma contribute significantly to gap closure, but there is evidence that anode plasma expansion results in a distortion of the effective anode shape, which can significantly affect the diode performance. Index Terms--Electron beams, particle beams, pinched-beam diodes, pulsed power, radiography.

A description of the underlying physics governing the operation of pulsed-power driven, gas-filled, paraxial diodes is presented. Gas-filled focusing cells are routinely used to transport high energy density electron beams for use in flash X-ray radiography experiments. The paraxial diode acts as a 1/4 betatron focusing element with a focal length F proportional to the square root of the beam energy and inversely proportional to the square root of the net current in the gas cell F [infinity] [([gamma]/[I.sub.net]).sup.1/2]. Particle-in-cell simulations demonstrate that the time integrated radiation spot is determined both by focal sweeping due to time varying net currents and by finite beam emittance. The calculated radiation focal plane, spot, and dose are compared to data obtained by the Atomic Weapons Establishment, U.K., from a variety of experimental configurations and demonstrate good agreement between simulation and experiment. Suggestions to improve the focal properties of the diode are presented. Index Terms--Beam-plasma propagation, betatron focusing, paraxial e-beams, pulsed power, X-ray radiography.

Equalizing image noise is shown to be an important step in the automatic detection of microcalcifications in digital mammography. This study extends a well established film-screen noise equalization scheme developed by Veldkamp et al. for application to full-field digital mammogram (FFDM) images. A simple noise model is determined based on the assumption that quantum noise is dominant in direct digital X-ray imaging. Estimation of the noise as a function of the gray level is improved by calculating the noise statistics using a truncated distribution method. Experimental support for the quantum noise assumption is presented for a set of step wedge phantom images. Performance of the noise equalization technique is also tested as a preprocessing stage to a microcalcification detection scheme. It is shown that the square root model based approach which FFDM allows leads to a robust estimation of the high frequency image noise. This provides better microcalcification detection performance when compared to the film-screen noise equalization method developed by Veldkamp. Substantially better results are obtained than when noise equalization is omitted. A database of 124 direct digital mammogram images containing 28 microcalcification clusters was used for evaluation of the method. Index Terms--Cancer, computer-aided diagnosis, noise measurement, X-ray imaging.

A new computing model has been implemented in Sindbad, a simulation software dedicated to radiographic systems, to provide quite rapidly realistic radiographs of complex objects, including the scatter component of the photon flux. The new computing model consists of a coupling of two previous models: an analytical approach and a Monte Carlo one. The analytical simulation is used to compute a high resolution uncollided photon flux image whereas the Monte Carlo provides the scattered flux image. This latter image is computed as a scaling of a reduced fluence Monte Carlo scattered flux image. Scaling is possible thanks to the low resolution feature of the scattered flux image. After a detailed description of the method developed to perform the combination, we present a validation on a medical radiograph simulation. In spite of the quite complex geometry of the examined part and the large number of emitted photons, this new computing model provides a realistic radiograph with a good estimation of the scattered flux in a reasonable computation time. Index Terms--Combination, Monte Carlo, scatter, simulation, uncollided.

Technologies currently used for cotton contaminant assessment suffer from some fundamental limitations. These limitations result in the misassessment of the cotton quality, and have a serious impact on its economic value. Through our research, we have shown that X-ray microtomographic image analysis may be applied with a high degree of success to noninvasive evaluation of cotton for the recognition of contaminants. We believe that this procedure, when realized in real time, will have a serious impact on the cotton cleaning process, and indeed on the economic value of cotton. Index Terms--Cotton trash, fuzzy classifier, image analysis, pattern classification, volumetric data, X-ray tomography.

An X pinch plasma is produced using two or more fine metal wires arranged so that they cross and touch at a single point, in the form of an 'X,' as the load of a pulsed power generator (pulser). X pinches produce very bright, small, short-lived sources of X-rays in the 1-10 keV range. The X-ray source size, pulse duration and photon energy spectra depend upon the wire material and diameter, and the current waveform from the pulser. Those with ~1 [micro]m source size can be used as point sources of X-ray radiation for point-projection radiography with high spatial resolution. We report experiments with a variety of different wire materials, including Al, Ti, Mo, W, among others, all of which produced high resolution images, and all of which have subnanosecond X-ray pulses for X-rays [greater than or equal to] 3 keV. X pinches produced using all of these materials had common development stages. However, the wire material and the rate of rise of the current pulse influenced the details of the dynamics, leading to variation in the timing of the X-ray burst(s) relative to the start of the current pulse. For a given wire material, wire diameter had only a small effect on X-ray emission timing. Final X pinch neck implosion speeds as high as 66-75 [micro]m/ns were estimated. Index Terms--Point X-ray source, short pulse X-ray source, X pinch, X-ray radiography, X-ray spectroscopy, Z pinch.

Contrast enhancement of radiographies based on a multiscale decomposition of the images recently has proven to be a far more versatile and efficient method than regular unsharp-masking techniques, while containing these as a subset. In this paper, we compare the performance of two multiscale-methods, namely the Laplacian Pyramid and the fast wavelet transform (FWT). We find that enhancement based on the FWT suffers from one serious drawback--the introduction of visible artifacts when large structures are enhanced strongly. By contrast, the Laplacian Pyramid allows a smooth enhancement of large structures, such that visible artifacts can be avoided. Only for the enhancement of very small details, for denoising applications or compression of images, the FWT may have some advantages over the Laplacian Pyramid. Index Terms--Fast wavelet transform, image enhancement, mammography, multiscale methods, radiography.

The rod-pinch diode is a cylindrical pinched-beam diode that provides an intense pulsed small-diameter bremsstrahlung source for radiography. For this work, the diode consists of a 1- to 6.4-mm-diameter anode rod that extends through the hole of an annular cathode. After exiting the cathode, wider anodes taper down to a 1 mm diameter. All of the anode rods then have a 1-mm-diameter tungsten tip that is usually tapered to a point. Rod-pinch diodes with anode rods of different materials, lengths, and diameters were powered by the Gamble H generator at peak voltages of 1.0 to 1.8 MV and peak currents of 30 to 60 kA. The radiation was characterized with temporally and spatially resolved X-ray diagnostics. Pinhole-camera images and time-resolved pin-diode measurements indicate that the radiation is emitted primarily from the vicinity of the rod tip. The dose measured with thermoluminescent detectors through a plexiglass transmission window ranges from 0.6 to 2.8 R at 1 m from the rod tip and the dose/charge scales faster than linearly with the diode voltage. The full-width at half-maximum (FWHM) of the radiation pulse is 30 to 50 ns. The size of the radiation source is determined by measuring its edge spread function. The source diameter, defined here as the FWHM of the derivative of the edge spread function, decreases from 2 mm for a 6.4-mm-diameter rod to 1 mm or less for a 1-mm-diameter rod. Analysis suggests that the central portion of the radiation distribution at the source can be approximated by a uniformly radiating circular disc. Index Terms--Critical current, electron beam diode, pinching, pulsed power, radiography, space-charge-limited current.

We constructed two small-area pixelated detectors, which can record signals produced by 800-MeV proton beam micropulses with a repetition rate of 358 ns. The first detector was built around a two-dimensional (2-D) photodiode array. The array was illuminated by light emitted by a monolithic 1.7-mm-thick lutetium oxy-orthosilicate (LSO) scintillator and imaged by a simple optical system. The other detector was a hydrogen ion chamber operated at 1 to 2.5 atm. The anode was divided into an array of 8 x 8 1 [mm.sup.2] pixels. The fast positive-ion drift velocity in hydrogen helps to minimize the space charge build up. However, for beam pulses spaced in time closer than 1 [micro]s, there appears to be a substantial accumulation of space charge. The electronic readout chain, for each of the 64 channels, consisted of an externally clocked fast-gated integrator and an amplifier coupled to an on-board analog-to-digital converter (ADC) and a first-in-first-out storage (FIFO). The detectors were tested with beam pulses up to 4 x [10.sup.6] protons per [mm.sup.2] delivered in 30 to 120 ns wide microbursts. Index Terms--Dynamic radiography, hydrogen gas-ion chamber, lutetium oxy-orthosilicate (LSO) scintillator, photodiode array, proton radiography detectors.

Gamma-ray imaging using quasi-monochromatic and energy-tunable photon beam was performed. The photon was produced by the laser-Compton backscattering of 300-800 MeV electrons with laser photons. Radiographs of several objects were measured using 3-20 MeV quasi-monochromatic photons. Index Terms--Compton scattering, gamma ray, imaging, laser, radiography.

An experimental study on hard X-ray pulses emitted by a small plasma focus is performed, regarding its application to biological radiographs in fast dynamic situations. It is found that the radiation intensity in a single shot is high enough to obtain fine resolution radiographs in very short exposures (about 10 ns). As an example, a radiograph on a live mouse is shown. It is found that the relation between responses of different detectors, i.e., thermoluminiscence dosimeters and scintillator-photomultiplier, is linear. Index Terms--Plasma focus, radiography, X-ray sources.

Tribo-chemical studies at the head/disk interface (HDI) were conducted on hydrogenated ([CH.sub.x]), nitrogenated ([CN.sub.x]), and cathodic-arc amorphous hard carbon disk samples coated with perfluoropolyether ZDOL and X1P/ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated [Al.sub.2][O.sub.3]-TiC sliders and thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber followed with a surface chemistry analysis by X-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The friction and catalytic decomposition mechanisms of ZDOL are described, as well as the tribo-chemical performance of cathodic-arc carbon overcoats coated with ZDOL, and data demonstrating the chemical alteration of the lubricant and carbon overcoat are also presented. Index terms - Cathodic-arc carbon, head/disk interface, NEXAFS, tribo-chemical studies, X-PEEM, ZDOL decomposition

Radiography is an effective method for nondestructive inspection of solid objects, but more complete analysis and diagnoses are possible with full 3-D reconstructions. The quantity of data available in radiography is seldom sufficient to form a deterministic estimate. We present methods for statistically optimal reconstructions of 3-D objects from small numbers of digitized radiographs, which not only restore more complete spatial information but also improve the detectability of aberrations and flaws in solid materials. The formulation includes scatter compensation under the statistical model.

We have designed and built a multi-channel cadmium telluride detector array to test its suitability as an X-ray imaging sensor for dual energy X-ray absorptiometry. The X-ray imaging sensor was constructed of 64 CdTe detector elements with high frequency current amplifiers, discriminators, and counters. The detector elements were operated in the photon counting mode and output pulses induced by the X-ray photons were separated into two energy levels according to their height. The energy resolution of the detector elements was 18.7% to 59.54 keV gamma-rays. In combination with a K-edge filter to produce dual energy X-rays, the X-ray imaging sensor was able to generate two energy X-ray images simultaneously over a short time. By applying a simple energy subtraction method to these images, bone phantoms were distinguished from the overlying tissue phantoms and their densities could be successfully measured. I was clearly demonstrated that this X-ray imaging sensor using CdTe crystals has good potential for high speed bone densitometry.

Heterojunctions made of sputter-deposited polycrystalline cadmium sulfide andcadmium telluride films are proposed as photonic sensors in X-ray imaging systems. The fabrication procedure is detailed along with a characterization ofthe heterojunction. Its adaptation to an X-ray imaging camera tube yields a device with a responsivity to X-ray radiation that is triple that of the standard PbO X-ray tube.

Current noninvasive or minimally invasive methods for evaluating in vivo knee kinematics are inadequate for accurate determination of dynamic joint function due to limited accuracy and/or insufficient sampling rates. A three-dimensional (3-D) model-based method is presented to estimate skeletal motion of the knee from high-speed sequences of biplane radiographs. The method implicitly assumes that geometrical features cannot be detected reliably and an exact segmentation of bone edges is not always feasible. An existing biplane radiograph system was simulated as two separate single-plane radiograph systems. Position and orientation of the underlying bone was determined for each single-plane view by generating projections through a 3-D volumetric model (from computed tomography), and producing an image (digitally reconstructed radiograph) similar (based on texture information and rough edges of bone) to the two--dimensional radiographs. The absolute 3-D pose was determined using known imaging geometry of the biplane radiograph system and a 3-D line intersection method. Results were compared to data of known accuracy, obtained from a previously established bone-implanted marker method. Difference of controlled in vitro tests was on the order of 0.5 mm for translation and 1.4 [degrees] for rotation. A biplane radiograph sequence of a canine hindlimb during treadmill walking was used for in vivo testing, with differences on the order of 0.8 nun for translation and 2.5 [degrees] for rotation. Index Terms--2-D/3-D image registration, digitally reconstructed radiograph (DRR), high-speed biplane radiographs, in vivo measurement, three-dimensional (3-D) model-based motion analysis.

We have revisited the physical mechanisms, which lead to a time delay of the onset of the undesirable spot size growth in high-dose X-ray radiography. In our theoretical model, the delay time is partially due to the time needed for the electron beam to thermally ionize the target spot resulting in target ions and partially due to the time needed for the ions to form a column of at least a quarter of the betatron wavelength of the electron beam. Based on our model, an analytic formula is derived, and it has been found to be consistent with experimental observations for different target materials and beam parameters. Our analysis shows that the delay time is directly proportional to the beam spot size at the target and inversely proportional to the beam current. Our calculations further show the spot size of the DARHT-1 beam with 2 kA current should be stable because the delay time of about 69 ns is longer than the beam pulse length. Index Terms--Beam-target interaction, electron beam spot, ion neutralization, radiography.

The aim of this paper is to describe a very general readout system for one-dimensional ionizing particles detectors. This system is based on a VME (Versa Module Eurocard, IEEE P1014, Mar. 12, 1987) bus which allows us to read and store up to 1000 channels in 1 ms. Thus, two-dimensional images can be recorded in a short time, for example by moving the measurement device composed of the detectors and their onboard electronics. This concept has been applied to a new low-dose X-ray radiology apparatus. A direct numerical radiographic image obtained with this system is presented. Index Terms--Digital acquisition, low dose, quantum detection, radiography, X-ray imaging.

Wire-array Z-pinches with low-density cylindrical foam targets on-axis have been used in inertial-confinement-fusion research on the 20-MA facility Z, but the effect of the targets on array performance is not fully understood. Experiments to investigate how the targets behave prior to array implosion, when they are bombarded by precursor plasma, have been carried out on the 1-MA MAGPIE generator. This paper presents data from X-pinch point-projection radiography, a primary diagnostic in these experiments. Index Terms--Dynamic hohlraum, non-imploding wire array, radiography, x-pinch, z-pinch.

X-pinches have been developed as point sources of soft X-rays for radiography, and are now routinely used for that purpose. Spatial resolution as good as 2 [micro]m and time resolution as good as a few 10 s of picoseconds has been obtained. Here, we present images from one of a very small number of tests in which a 450-kA, 100-ns pulse was divided among three X-pinches in parallel, and each of the three emitted an X-ray burst that was used for radiography of one or both of the other two. Index Terms--Exploding-wire z-pinch, X-pinch plasma, X-ray radiography.