Low Exposure X-ray Transmission Measurements for Contrast Media Detection with Filtered X-rays

Characteristic-line radiation from heavy metal targets bombarded by MeV proton beams has been tested as an X-ray source for dual-energy K-edge subtraction imaging for human angiography (blood vessel imaging) based on iodinated contrast media. To utilize the strong absorption by iodine (Z = 53) at its K-absorption edge (33.2 keV), we used K α-line of La (lanthanum, Z = 57) at 33.4 keV. As a reference, also K α X emission of Sn (tin, Z = 50) at 25.2 keV was employed. Metallic plates of La and Sn were irradiated by 7-MeV protons to produce these characteristic X-rays. Energy-subtraction method was tested using Lucite phantoms which contain aqueous solutions of KI (potassium iodide) with different concentrations. Also Ca ( H 2 PO 4)2 powder was stuffed in these phantoms to simulate bones. The transmission images of the phantoms were recorded on imaging plates. During the exposure, the energy spectra of the X-rays were monitored by a CdTe detector. We found that the contrast of images of iodide solutions taken with La X-rays was higher than that with Sn X-rays. Also the energy subtraction procedure was successfully applied to reduce the graphical noise due to the bones and inhomogeneity of the soft tissue. However, to apply the present method to actual clinical use, the X-ray intensity must be increased by several orders of magnitude. Also the transmission of the “lower-energy” photons has to be a few orders higher for imaging of objects as thick as human chest.

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Quantitative X-ray analysis of thin samples in Tem

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109641 ◽

1978 ◽

Vol 36 (1) ◽

pp. 500-501

Author(s):

I. Pozsgai ◽

N.P. Ilyinxx

Keyword(s):

Bragg Reflection ◽

Exponential Dependence ◽

X Rays ◽

X Ray ◽

Cu Films ◽

Electron Transmission ◽

Mass Thickness ◽

Transmission Measurements ◽

Image Position ◽

Thin Samples

The intensity of characteristic x-rays /IiX/ from thin self-supporting samples depends not only on the concentration /c/ of the excited element but also on the mass thickness /ƍD/ of the film:The ki factors can be determined on thin etalon films of known thickness. So as to carry out quantitative analysis of thin samples, it is necessary to measure the local ƍ D independently of the measurement of x-ray intensities.In this paper a method is described to determine the mass thickness of thin samples by electron transmission and their chemical composition by combining the x-ray intensity and electron transmission measurements.It is known that some polycrystalline films e.g. Au, Ag, Sb, Bi and Cu films, exhibit anomalous behaviour in the exponential dependence of electron transmission on ƍD. Therefore we have developed a method for the measurement of electron transmission which overcomes the influence of Bragg reflection electrons.

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White-Light Coronal Structures: Streamers and CMEs

International Astronomical Union Colloquium ◽

10.1017/s0252921100025045 ◽

1994 ◽

Vol 144 ◽

pp. 82

Author(s):

E. Hildner

Keyword(s):

Emission Line ◽

Electron Density ◽

White Light ◽

Coronal Mass Ejections ◽

X Rays ◽

Solar Cycles ◽

Temperature Function ◽

X Ray ◽

Eclipse Observations ◽

Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

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Chemical Species Identification in an SEM by Changes in Emitted X-Ray Energies

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100052869 ◽

1974 ◽

Vol 32 ◽

pp. 570-571

Author(s):

R. H. Duff

Keyword(s):

Species Identification ◽

Valence Electron ◽

Chemical Species ◽

X Rays ◽

Chemical Bonds ◽

Small Shift ◽

X Ray ◽

Electron Transitions ◽

Peak Energy ◽

Chemical Combination

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.

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Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079164 ◽

1977 ◽

Vol 35 ◽

pp. 328-329

Author(s):

E. A. Kenik ◽

J. Bentley

Keyword(s):

Thin Foil ◽

Electron Excitation ◽

Simple Approach ◽

Foil Thickness ◽

X Rays ◽

X Ray ◽

Hole Spectrum ◽

Illumination System ◽

Thin Foils ◽

Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

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X-ray micro tomography in the scanning electron microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100107678 ◽

1978 ◽

Vol 36 (1) ◽

pp. 106-107 ◽

Cited By ~ 1

Author(s):

W. Brünger

Keyword(s):

Electron Beam ◽

Electron Microscope ◽

Scanning Electron Microscope ◽

Target Surface ◽

The Body ◽

X Rays ◽

Cross Sectional ◽

X Ray ◽

Micro Tomography ◽

Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

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Digital x-ray mapping of nanometer-size supported bimetallic catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104716 ◽

1988 ◽

Vol 46 ◽

pp. 530-531

Author(s):

L. T. Germinario

Keyword(s):

Background Radiation ◽

Metal Cluster ◽

Single Element ◽

Beam Diameter ◽

X Rays ◽

X Ray ◽

Major Interest ◽

Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

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X-ray diffraction properties of curved crystal diffractors

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133308 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1734-1735

Author(s):

W. Z. Chang ◽

D. B. Wittry

Keyword(s):

Diffraction Theory ◽

X Rays ◽

Diffraction Image ◽

X Ray Diffraction ◽

Rocking Curve ◽

X Ray ◽

Bent Crystal ◽

Diffraction Geometry ◽

Crystal Parameter ◽

Quantitative Procedure

Since Du Mond and Kirkpatrick first discussed the principle of a bent crystal spectrograph in 1930, curved single crystals have been widely utilized as spectrometric monochromators as well as diffractors for focusing x rays diverging from a point. Curved crystal diffraction theory predicts that the diffraction parameters - the rocking curve width w, and the peak reflection coefficient r of curved crystals will certainly deviate from those of their flat form. Due to a lack of curved crystal parameter data in current literature and the need for optimizing the choice of diffraction geometry and crystal materials for various applications, we have continued the investigation of our technique presented at the last conference. In the present abstract, we describe a more rigorous and quantitative procedure for measuring the parameters of curved crystals.The diffraction image of a singly bent crystal under study can be obtained by using the Johann geometry with an x-ray point source.

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Studies of metaphase chromosomes in the scanning transmission x-ray microscope: Image fidelity, radiation damage and specimen preparation

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129826 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1038-1039

Author(s):

Shawn Williams ◽

Xiaodong Zhang ◽

Susan Lamm ◽

Jack Van’t Hof

Keyword(s):

Visible Light ◽

Radiation Damage ◽

Cross Section ◽

Imaging Techniques ◽

Dose Range ◽

Specimen Preparation ◽

X Rays ◽

Metaphase Chromosomes ◽

X Ray ◽

Scanning Transmission

The Scanning Transmission X-ray Microscope (STXM) is well suited for investigating metaphase chromosome structure. The absorption cross-section of soft x-rays having energies between the carbon and oxygen K edges (284 - 531 eV) is 6 - 9.5 times greater for organic specimens than for water, which permits one to examine unstained, wet biological specimens with resolution superior to that attainable using visible light. The attenuation length of the x-rays is suitable for imaging micron thick specimens without sectioning. This large difference in cross-section yields good specimen contrast, so that fewer soft x-rays than electrons are required to image wet biological specimens at a given resolution. But most imaging techniques delivering better resolution than visible light produce radiation damage. Soft x-rays are known to be very effective in damaging biological specimens. The STXM is constructed to minimize specimen dose, but it is important to measure the actual damage induced as a function of dose in order to determine the dose range within which radiation damage does not compromise image quality.

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High spatial resolution x-ray microanalysis of interfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100137793 ◽

1995 ◽

Vol 53 ◽

pp. 284-285

Author(s):

J. R. Michael

Keyword(s):

Spatial Resolution ◽

Electron Probe ◽

Solid Angle ◽

Collection Efficiency ◽

Spatial Scales ◽

Energy Dispersive Spectrometer ◽

X Rays ◽

X Ray ◽

Probe Size ◽

Brightness Field

X-ray microanalysis in the analytical electron microscope (AEM) refers to a technique by which chemical composition can be determined on spatial scales of less than 10 nm. There are many factors that influence the quality of x-ray microanalysis. The minimum probe size with sufficient current for microanalysis that can be generated determines the ultimate spatial resolution of each individual microanalysis. However, it is also necessary to collect efficiently the x-rays generated. Modern high brightness field emission gun equipped AEMs can now generate probes that are less than 1 nm in diameter with high probe currents. Improving the x-ray collection solid angle of the solid state energy dispersive spectrometer (EDS) results in more efficient collection of x-ray generated by the interaction of the electron probe with the specimen, thus reducing the minimum detectability limit. The combination of decreased interaction volume due to smaller electron probe size and the increased collection efficiency due to larger solid angle of x-ray collection should enhance our ability to study interfacial segregation.

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