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[en] Highlights: • Mono-energetic reconstructions in dual-layer spectral detector CT improve image quality compared to poly-energetic images. • Noise levels and CNR were better for mono-energetic reconstructions compared to conventional images in contrast-enhanced chest CT. • Whether mono-energetic images have added diagnostic value compared to conventional images, is still unknown. - Abstract: Objectives: To evaluate image quality parameters of virtual mono-energetic (MonoE) and conventional (CR) imaging derived from a dual-layer spectral detector CT (DLCT) in oncological follow-up venous phase imaging of the chest and comparison with conventional multi-detector CT (CRMDCT) imaging. Materials and methods: A total of 55 patients who had oncologic staging with conventional CT and DLCT of the chest in venous phase were included in this study. Established image quality parameters were derived from all datasets in defined thoracic landmarks. Attenuation, image noise, and signal-/contrast- to noise ratios (SNR, CNR) were compared between CRDLCT and MonoE as well as CRMDCT imaging. Two readers performed subjective image analysis. Results: CRMDCT showed significant lower attenuation values compared to CRDLCT and MonoE at 40–70 keV (p ≤ 0.05). Moreover, MonoE at 40–70 keV revealed significantly higher attenuations values compared to CRDLCT (p < 0.001). Noise was statistically lower in CRMDCT compared with CRDLCT and MonoE at 40 keV (11.4 ± 2.3 HU vs. 12.0 ± 3.1 HU vs. 11.7 ± 5.2 HU; p < 0.001). In contrast, all MonoE levels showed significantly lower noise levels compared to CRDLCT (p < 0.001). SNR was not significantly different between CRMDCT and CRDLCT (13.5 ± 3.7 vs. 14.4 ± 5.3; p > 0.99). SNR values were significantly increased for MonoE at 40–80 keV compared to CRMDCT and CRDLCT (p < 0.001). CRDLCT and MonoE (40–70 keV) from DLCT revealed significantly higher CNR values than CRMDCT (p < 0.001). In subjective analysis, MonoE at 40 keV surpassed all other image reconstructions except for noise in MonoE at 70 keV. Conclusion: In dual-layer spectral detector CT, MonoE at low keV showed superior image quality compared to conventional images derived from the same system and may therefore be added to clinical routine imaging protocols. Whether MonoE reconstructions yield additional diagnostic information is still unknown.
[en] Progress made in developing a facility for measurement of X-ray attenuation coefficients is outlined and results obtained are presented. A collimated broad spectrum X-ray is allowed to pass through a sample before being monochromated by a collimated, energy-dispersive intrinsic germanium detector. Attenuation measurements were performed on samples of pure crystalline silicon
[en] The neutron importance function in a nuclear fission reactor can be determined by means of the usual radioactive neutron sources only down to a lower energy limit of about 20 keV. The energy range can be extended to epithermal energies if a polyethylene moderated Sb-Be-photoneutron source is used. The results of experimental and theoretical investigation are given concerning the determination of the source spectrum and the source strength and regarding the pecularities of the pseudo-reactivity measurements by means of the moderated Sb-Be-source. Determining the neutron importance function in the fast substituted lattice SEG-III of the Rossendorf annular core reactor RRR the usefulness of this novel source and of the source parameters ascertained are confirmed. (orig.)