Josef-Marie Dr. Kosanetzky

X‐ray diffraction computed tomography

Coherent scattering of x-ray photons leads to the phenomenon of x-ray diffraction, which is widely used for determining atomic structure in materials science. A technique [x-ray diffraction computed tomography (CT)] is described, analogous to conventional CT, in which the x-ray diffraction properties of a stack of two-dimensional object sections may be imaged. The technique has been investigated using a first generation (single pencil beam) CT scanner to measure small angle coherent scatter, in addition to the customary transmitted radiation. Diffraction data from a standard CT performance phantom obtained with this new technique and with an x-ray diffractometer are compared. The agreement is satisfactory bearing in mind the poor momentum resolution of our apparatus. The dose and sensitivity of x-ray diffraction CT are compared with those of conventional transmission CT. Diffraction patterns of some biological tissues and plastics presented in a companion paper indicate the potential of x-ray diffraction CT for tissue discrimination and material characterization. Finally, possibilities for refinement of the technique by improving the momentum resolution are discussed.

X-Ray diffraction measurements of some plastic materials and body tissues

X-ray diffraction allows the investigation of the atomic or molecular structure of materials. The combination of diffractometry with computerized tomography enables spatially resolved imaging of the diffraction properties of extended objects as described in more detail in a companion article [Harding et al., Med. Phys. 14, 515 (1987)]. We present measured diffraction patterns of some plastics and several biological materials, which allow further optimization of our method and the selection of suitable application areas.

Elastic scatter computed tomography

A technique is proposed for imaging 2D sections based on measurement of elastic scatter radiation. In this new imaging method the radiation from a conventional X-ray source (Philips MCN 165 160 kVp tube operated at 140 kVp and 4.6 mA with 0.6 mm focus) is collimated by a lead diaphragm (1.0 mm) and falls on the object to be investigated. The transmitted radiation and the scatter falling within a range of half-angle 6 degrees (with reference to the object centre) are recorded by seven scintillation detectors (BGO) operated in current integration mode. Each scintillation crystal subtends an angular range of 1 degrees . The detector array comprises three scatter detectors arranged symmetrically on either side of the central transmission detector in such a way that six (partially overlapping) scatter measurements result.

Coherent scatter in radiographic imaging: a Monte Carlo simulation study

The significance of coherently scattered radiation in radiographic imaging is investigated using the Monte Carlo simulation technique. Recent data on the form factor of liquid water, which take into account intermolecular interference effects, have been used for the calculation of the coherent differential cross section. The spatial distribution of scattered radiation in the detection plane was calculated separately for coherent and incoherent single and multiple scattering. In the pencil beam geometry, it is found that coherent scattering leaving the object, is almost exclusively single scattering, is concentrated near but not exactly at the transmitted primary beam and dominates over multiple incoherent scattering in this region even for thick objects and polyenergetic radiation. Some consequences concerning the performance of grids, the choice of phantom materials and a new imaging method are given.

A new fluorescent X-ray source for photon scattering investigations

A description is given of the design and performance of a novel fluorescent X-ray source, comprising a demountable conical target enclosed in a conical anode X-ray tube. Measurements are presented of the spectral purity of the fluorescent emission and the variation in photon flux with the applied tube voltage. A Ta target tube (Kalpha 1=57.532 keV) powered by a standard 3.75 kW, 160 kV high voltage generator has a source brightness of 109 photons/s sr mm2. This is 500 times greater than that of the brightest available 241-Am radionuclide sources. Some potential applications of the fluorescent X-ray source are listed.

Energy Resolved X-Ray Diffraction CT

Low angle x-ray scattering at diagnostic energies in narrow beam geometry is due to coherent (Rayleigh) and incoherent (Compton) scattering. It has been found that single coherent scatter dominates below 10 deg. Interference effects with coherent scatter leads to diffraction patterns which differ from material to material. A technique, analogous to conventional CT, allows the reconstruction of the 2D distribution of the x-ray diffraction properties within an object slice, as demonstrated recently? Use of the bremsstrahlung spectrum of an x-ray tube permits short measuring times, but causes a significant energy broadening of the diffraction curves, thus deteriorating the maximum contrast obtainable by diffraction imaging. With energy resolved photon counting of the scattered x-ray quanta this broadening can be corrected, yielding an image contrast approaching that of a monochromatic x-ray source.