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Biomedical subjects

U Neitzel

Publications and source records attributed to U Neitzel.

5 recordsLinked to original sources
PubMed1985

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.

Humans↗
PubMedDate not supplied

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.

Computers↗
PubMedDate not supplied

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.

Humans↗
PubMedDate not supplied

Grids or air gaps for scatter reduction in digital radiography: a model calculation.

The relative advantages of grids and air gaps for scatter reduction in a digital radiography system were investigated using a theoretical model. In this model the properties of the scatter reduction device are described by primary transmission and selectivity. The signal-to-noise (SNR) improvement factor for fixed exposure to the patient was used as a performance indicator. The results show that the SNR improvement depends strongly on the local scatter fraction; for all practical configurations, however, it stays below a factor of 2. For high scatter fractions, an air gap of 20 cm has about the same effect on SNR improvement as a highly selective grid; for low and medium scatter conditions the air gap performs better than any grid. Additive system noise reduces the SNR improvement factor compared to the case with quantum noise only, the reduction being more pronounced for the grids than for the air gap. The results suggest that the use of an air gap instead of a grid is advantageous in digital radiography systems.

Models, Theoretical↗