X-ray Image Sequences Research Articles

A Robust 3-D IVUS Transducer Tracking Using Single-Plane Cineangiography

During an intravascular ultrasound (IVUS) intervention, a catheter with an ultrasound transducer is introduced in the body through a blood vessel, and then, pulled back to image a sequence of vessel cross sections. Unfortunately, there is no 3-D information about the position and orientation of these cross-section planes, which makes them less informative. To position the IVUS images in space, some researchers have proposed complex stereoscopic procedures relying on biplane angiography to get two X-ray image sequences of the IVUS transducer trajectory along the catheter. To simplify this procedure, we and others have elaborated algorithms to recover the transducer 3-D trajectory with only a single view X-ray image sequence. In this paper, we present an improved method that provides both automated 2-D and 3-D transducer tracking based on pullback speed as a priori information. The proposed algorithm is robust to erratic pullback speed and is more accurate than the previous single-plane 3-D tracking methods.

X-Ray Radioscopic Visualization of the Solutal Convection during Solidification of a Ga-30 Wt Pct In Alloy

Capabilities of the X-ray attenuation contrast radioscopy were used to provide a real-time diagnostic technique of the melt flow during unidirectional solidification of a Ga-30 wt pct In alloy from the bottom, which is significantly affected by solutal convection. The solidification process was visualized using a microfocus X-ray tube. The X-ray facility provided shadow radiographs at spatial resolutions of about 10 μm at frame repetition rates of 25 Hz. The optical flow approach was used to derive information about the velocity field ahead of the solidification front and in the mushy zone from the observed displacement of the brightness patterns appearing during the X-ray image sequence. Buoyancy-driven flow patterns were found at length scales much larger than the length scales of the solidifying microstructure. A strong coupling between convection and dendritic growth became apparent via flow-induced modifications of the concentration profile in the liquid.

Can magnetic resonance imaging–derived bone models be used for accurate motion measurement with single‐plane three‐dimensional shape registration?

The purpose of this study was to compare three-dimensional (3D) kinematic measurements from single-plane radiographic projections using bone models created from magnetic resonance imaging (MRI) and computed tomography (CT). MRI is attractive because there is no ionizing radiation, but geometric field distortion and poor bone contrast degrade model fidelity compared to CT. We created knee bone models of three healthy volunteers from both MRI and CT and performed three quantitative comparisons. First, differences between MRI- and CT-derived bone model surfaces were measured. Second, shape matching motion measurements were done with bone models for X-ray image sequences of a squat activity. Third, synthetic X-ray images in known poses were created and shape matching was again performed. Differences in kinematic results were quantified in terms of root mean square (RMS) error. Mean differences between CT and MRI model surfaces for the femur and tibia were -0.08 mm and -0.14 mm, respectively. There were significant differences in three of six kinematic parameters comparing matching results from MRI-derived bone models and CT-derived bone models. RMS errors for tibiofemoral poses averaged 0.74 mm for sagittal translations, 2.0 mm for mediolateral translations, and 1.4 degrees for all rotations with MRI models. Average RMS errors were 0.53 mm for sagittal translations, 1.6 mm for mediolateral translations, and 0.54 degrees for all rotations with the CT models. Single-plane X-ray imaging with model-based shape matching provides kinematic measurements with sufficient accuracy to assess knee motions using either MRI- or CT-derived bone models. However, extra care should be taken when using MRI-derived bone models because model inaccuracies will affect the quality of the shape matching results.

Simulated X‐Ray Emission for a Runaway Model of Kepler's Supernova Remnant

We present two-dimensional numerical simulations of a model for Kepler's supernova remnant (SNR) carried out with the YGUAZU-A code. Following previous studies, we have assumed that the peculiar shape of this young remnant arises as a consequence of the interaction of the SNR blast wave with the bow shock formed by the wind of its high velocity progenitor. Furthermore, from our numerical results we have obtained synthetic X-ray emission maps, which can be directly compared with recent and previous observations of this SNR. Our models show that a nice fit with respect to the X-ray morphology and luminosity is obtained for a SN progenitor with mass-loss rate of 5 x 10(-5) M-circle dot yr(-1), an ambient medium density of 10(-2) cm(-3), an initial explosion energy of 8 x 10(50) ergs, and a total ejected mass within 1.4-2.5 M-circle dot. In our simulations, parameters typical of a young population progenitor have not been considered. This model also predicts a similar to 0.3% yearly decrease in the total X-ray luminosity, which is consistent with observed values. The parameters employed in our runs correspond to a Type Ia supernova. Based on our simulations, we find that the expansion rate increases after the SNR blast wave overruns the bow shock, and we discuss whether this can explain the observed difference between the expansion rates measured from sequences of radio and X-ray images. (Less)

Quantitative chemical mapping of sodium acrylate- and N-vinylpyrrolidone-enhanced alginate microcapsules

Alginate microcapsules enclosing recombinant cells secreting therapeutic products have been used successfully to treat several murine models of human diseases. The mechanical and chemical properties of these alginate capsules can be improved by the addition and in situ photopolymerization of sodium acrylate and N-vinylpyrrolidone in the alginate capsule. The purpose of this modification was to form additional covalent cross-links. In this work we have used scanning transmission X-ray microscopy (STXM) to probe the nature and location of the chemical modifications in the modified capsules by comparison with unmodified capsules. Analysis of X-ray image sequences and selected area spectra has been used to map the calcium gradient in capsules, to identify the presence of polyacrylate throughout the capsules and the localization of poly-N-vinylpyrrolidone in the outer regions of the alginate capsules. The differences in the spatial distributions of these species have led to better understanding of the chemical modifications that provide a mechanically more stable capsule structure.

A 3-D space–time motion detection for an invariant image registration approach in digital subtraction angiography

A serious problem encountered in digital subtraction angiography (DSA) is the presence of artifacts due to patient motion. The resulting artifacts which arise from the misalignment of successive images in the sequence frequently reduce the diagnostic value of the images and lead to misdiagnosis or rejection of a DSA image sequence. A possible solution is the use of image registration techniques. In this paper, an invariant approach to elastic registration based on local similarity detection according to a combined invariants-based similarity measure, in which the images are locally registered and elastically interpolated, is presented. To improve the registration, a 3-D space–time motion-detection technique for extracting movement point pairs in a sequence of X-ray images is proposed. It is shown that such a technique is very efficient to correct for both global and local motion artifacts. The proposed algorithm for this technique has been successfully applied to register several clinical data sets including coronary applications. The results show that a fast and accurate image registration is achieved and that the algorithm is robust, which makes it clinically applicable.

Tracing Rib Contour Lines by Respiratory Motion Compensation from an X-ray Image Sequence

Tracing Rib Contour Lines by Respiratory Motion Compensation from an X-ray Image Sequence

An invariant approach for image registration in digital subtraction angiography

In modern medicine, digital subtraction angiography is a powerful technique for the visualization of blood vessels in a sequence of X-ray images. A serious problem encountered in this technique is misregistration of images due to patient motion. The resulting artifacts which arise from the misalignment of successive images in the sequence frequently reduce the diagnostic value of the images. In this paper, a new approach to the registration of digital angiographic image sequences is proposed. It is based on local similarity detection by means of template matching according to a combined invariants-based similarity measure and on thin-plate spline image warping. This technique is fully automatic and very efficient to correct for patient motion artifacts. The proposed algorithm for this technique has been successfully applied to register several clinical data sets including coronary applications. It works perfectly well for both slow and sudden motions and is both effective and fast.

Improved localization of coronary stents using layer decomposition.

Accurate placement and expansion of coronary stents is hindered by the fact that most stents are only slightly radiopaque and hence difficult to see in typical coronary X-ray images. We propose a new technique for improved image guidance of multiple coronary stent deployment using layer decomposition of coronary X-ray image sequences. We hypothesize that layer decomposition can improve the accuracy of localization of the end of a deployed stent. Layer decomposition is used to obtain good quality images of a stent in vitro. The resultant background-subtracted stent images are embedded into other cine X-ray image sequences to form a database of simulated image sequences. For each simulated sequence, the position of the stent edge is estimated from raw and layer-decomposed images using a small region of the original layer image as a template. Layer decomposition reduced median position errors in 33 of 47 image sequences (70%), including 16 of 18 sequences in which the position errors for raw and layer images differed by 5.0 pixels (0.5 mm) or more. Layer decomposition significantly reduces errors in determination of stent edge location in simulated cine X-ray image sequences.

Improved Localization of Coronary Stents Using Layer Decomposition

Accurate placement and expansion of coronary stents is hindered by the fact that most stents are only slightly radiopaque and hence difficult to see in typical coronary X-ray images. We propose a new technique for improved image guidance of multiple coronary stent deployment using layer decomposition of coronary X-ray image sequences. We hypothesize that layer decomposition can improve the accuracy of localization of the end of a deployed stent. Layer decomposition is used to obtain good quality images of a stent in vitro. The resultant background-subtracted stent images are embedded into other cine X-ray image sequences to form a database of simulated image sequences. For each simulated sequence, the position of the stent edge is estimated from raw and layer-decomposed images using a small region of the original layer image as a template. Layer decomposition reduced median position errors in 33 of 47 image sequences (70%), including 16 of 18 sequences in which the position errors for raw and layer images differed by 5.0 pixels (0.5 mm) or more. Layer decomposition significantly reduces errors in determination of stent edge location in simulated cine X-ray image sequences.

A 3D space–time motion evaluation for image registration in digital subtraction angiography

In modern clinical practice, Digital Subtraction Angiography (DSA) is a powerful technique for the visualization of blood vessels in a sequence of X-ray images. A serious problem encountered in this technique is the presence of artifacts due to patient motion. The resulting artifacts frequently lead to misdiagnosis or rejection of a DSA image sequence. In this paper, a new technique for removing both global and local motion artifacts is presented. It is based on a 3D space–time motion evaluation for separating pixels changing values because of motion from those changing values because of contrast flow. This technique is proved to be very efficient to correct for patient motion artifacts and is computationally cheap. Experimental results with several clinical data sets show that this technique is very fast and results in higher quality images.

Soft x-ray spectroscopy from image sequences with sub-100 nm spatial resolution.

A method is described whereby a sequence of X-ray images at closely spaced photon energies is acquired using a scanning transmission X-ray microscope, and aligned. Near-edge absorption spectra can then be obtained both from large, irregular regions, and from regions as small as the spatial resolution of the microscope (about 40 nm in the examples shown here). The use of the technique is illustrated in examination of a layered polymer film, a micrometeorite section, and an interplanetary dust particle section.

Statistical deformable model-based segmentation of image motion

We present a statistical method for the motion-based segmentation of deformable structures undergoing nonrigid movements. The proposed approach relies on two models describing the shape of interest, its variability, and its movement. The first model corresponds to a statistical deformable template that constrains the shape and its deformations. The second model is introduced to represent the optical flow field inside the deformable template. These two models are combined within a single probability distribution, which enables to derive shape and motion estimates using a maximum likelihood approach. The method requires no manual initialization and is demonstrated on synthetic data and on a medical X-ray image sequence.

Tracking of non-rigid articulatory organs in X-ray image sequences

This article presents a system for the automated tracking of non-rigid anatomic structures in two-dimensional image sequences, which was primarily applied to X-ray image sequences of the vocal tract. In this particular application articulatory organs have to be measured to investigate the complex dynamic characteristics of human speech production. Of particular interest is a robust boundary detection of non-rigid organs such as lips and tongue. To solve this ill-posed detection problem under the presence of transparently superimposing structures, varying textural appearances of organs and noise, a two-level system is proposed. At the lower level, several edge-, region-, and motion-based image operators are combined to exploit their respective benefints and concomitantly compensate for their deficiencies. For the sake of precision, the result of these operators are not represented as larger tokens, such as line segments, but remain pixel-related cues or image evidences. At the higher level, an active contour-based component allows for the introduction of a priori knowledge about the object to be detected.

ニューラルフィルタを用いた医用低線量X線動画像の画質改善

ニューラルフィルタを用いた医用低線量X線動画像の画質改善

The influence of horizontal internal baffles on the flow pattern in dense fluidized beds by X-ray investigation

The influence of horizontally placed internals on the physical behaviour of a dense fluidized bed has been observed using an X-ray technique. The internals were sieve-like baffles with an aperture size two orders of magnitude larger than the diameter of the bed particles. Both a freely bubbling bed and single injected bubbles were observed. For the latter, the bubbles were made to emerge from a layer more opaque to X-rays into one more transparent. In this way, the flow pattern around the bubble and the wake could be observed. The results show that the baffles do not influence the mean bubble size or velocity significantly, confirming earlier indirect observations. It is also shown that the wake material is removed from the fluidization bubbles by the baffles. Results are given as statistics for bubble size and rise velocity as a function of the fluidization velocity with and without baffles present, and sequences of X-ray images showing the effect of the baffles.

Time-Resolved, Multi-frame X-Ray Imaging of Laser-Produced Plasmas

A novel x-ray imaging system based on a microchannel-plate combined with a multi-pinhole camera has been employed to study x-ray emission from laser-produced plasmas in the 0.5–3 keV photon energy range. In particular, the interaction of intense laser radiation with such plasmas, under conditions relevant to inertial confinement fusion, was monitored by recording a sequence of consecutive x-ray images with a temporal resolution of 140 ps and a spatial resolution of 10 μm. These images provide valuable information on the main physical mechanisms involved in the interaction process, including collisional absorption of the incident laser energy and electron thermal conduction.

Time-Resolved, Multi-frame X-Ray Imaging of Laser-Produced Plasmas

A novel x-ray imaging system based on a microchannel-plate combined with a multi-pinhole camera has been employed to study x-ray emission from laser-produced plasmas in the 0.5-3 keV photon energy range. In particular, the interaction of intense laser radiation with such plasmas, under conditions relevant to inertial confinement fusion, was monitored by recording a sequence of consecutive x-ray images with a temporal resolution of 140 ps and a spatial resolution of 10 μm. These images provide valuable information on the main physical mechanisms involved in the interaction process, including collisional absorption of the incident laser energy and electron thermal conduction.

VERY LARGE ARRAY OBSERVATIONS OF EVOLVING NOISE STORM SOURCES ON THE SUN

The presence of coronal magnetic fields connecting active regions is inferred from decimetric observations of solar noise storms with the Very Large Array (VLA) and from soft X-ray images taken by Yohkoh. Temporal changes in the noise storms appear to be correlated with some soft X-ray bursts detected by both Yohkoh and the GOES satellite. Combined analysis of the radio and X-ray data suggests a re-arrangement of the coronal magnetic field during the onset of impulsive noise storm burst emission. On one day during the combined VLA–Yohkoh–GOES observations, two widely-separated active regions appear to be connected by a faint trans-equatorial 91 cm source as well as two distinct soft X-ray loops. The two active regions show anti-correlated fluctuations in decimetric radio emission. On another day of combined VLA–Yohkoh observations, a series of 91 cm noise storm bursts are observed along the major axis of the associated noise storm continuum. Time sequences of Yohkoh soft X-ray images show a contraction of coronal loops prior to the onset of this series of bursts and a corresponding increase in the X-ray flux in the apparent footpoint of the overarching loop containing the noise storm. These observations imply that energy from a realignment of the magnetic field is being transferred, possibly by accelerated particles, along loops connecting separated active regions on the Sun.

Recognition and tracking of articulatory organsin X-ray image sequences

Deformable organs of the human vocal tract are detected. An active contour is optimised by a dynamic programming algorithm, for which a new constraint is presented that introduces a priori knowledge on the shape of the expected boundary. The algorithm is able to detect convex and concave objects even when the image quality is poor.