PubMed Health⌕ Search

Biomedical subjects

A J Talbert

Publications and source records attributed to A J Talbert.

5 recordsLinked to original sources
PubMed1982

The use of phantom views to reduce CT streaks due to insufficient angular sampling.

An artefact that can occur in CT scans with too few views is the appearance of streaks at some distance from the sharp edge that causes them. We investigate, for parallel beam scanners, the effectiveness of the method of phantom views, as well as other methods of angular interpolation, in diminishing the view-limited streak artefact. The phantom view method consists of inserting data points obtained by interpolation in angle, along with the real data points. We show by a theoretical analysis, as well as by using simulated scans, that the phantom view method does tend to diminish the distant streaks more than other methods tested. Furthermore, we show that there is a point of diminishing returns in increasing the number of phantom views.

Technology, Radiologic↗
PubMed1980

Noise factor of a polyenergetic x-ray beam in computed tomography.

The attenuation characteristics of a polyenergetic x-ray beam in computed tomography can be completely specified by two parameters: the spectral factor, which in turn provides an equivalent single energy, and the noise factor, which describes the noise characteristics of the polyenergetic beam relative to its single-energy equivalent. Noise factors of typical spectra have been calculated. It is found that only moderate filtration is required to bring the noise factors near unity, indicating that there is little increase in image noise caused by the use of polyenergetic spectra. By using noise factor as an analytic tool, it is possible to optimise the filtration for the desired adjustment between noise, scan time, and dose.

Physical Phenomena↗
PubMed1980

Optimum energies for dual-energy computed tomography.

By performing a dual-energy scan, separate information can be obtained on the Compton and photoelectric components of attenuation for an unknown material. This procedure has been analysed for the optimum energies, and for the optimum dose distribution between the two scans. It is found that an equal dose at both energies is a good compromise, compared with optimising the dose distribution for either the Compton or photoelectric components individually. For monoenergetic beams, it is found that low energy of 40 keV produces minimum noise when using high-energy beams of 80-100 keV. This is true whether one maintains constant integral dose or constant surface dose. A low energy of 50 keV, which is more nearly attainable in practice, produces almost as good a degree of accuracy. The analysis can be extended to polyenergetic beams by the inclusion of a noise factor. The above results are qualitatively unchanged, although the noise is increased by about 20% with integral dose equivalence and 50% with surface dose equivalence. It is very important to make the spectra as narrow as possible, especially at the low energy, in order to minimise the noise.

Physical Phenomena↗