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  • 1. Hammersberg, P.
    et al.
    Stenström, Mats
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Maximising the signal-to-noise ratio in computerised tomography data using robust design1996In: Insight (Northampton), ISSN 1354-2575, E-ISSN 1754-4904, Vol. 38, no 2, p. 112-117Article in journal (Refereed)
    Abstract [en]

    Image quality in Computerised Tomography (CT) depends strongly on the quality of the CT-projection data, which vary with the imaged sample and the equipment used. The objective has been to find a setting of the CT-scanner Control Factors (CF) maximising the signal-to-noise ratio in CT projection data (SNRCT) of a contrasting detail (for example a defect) and a surrounding cylindrical sample, and to present a general optimisation methodology. An optimisation case study was carried out, valid for a CT-scanner equipped with a polyenergetic X-ray source (conventional) with tungsten target and a partially energy-integrating detector system (image intensifier and optical video chain), with and without consideration qf the exposure limits associated with the microfocal X-ray source used. The CF of interest were tube potential, exposure (product of tube current and exposure time), material and thickness of the primary filter, optical aperture and attenuation equalising filter design. The settings yielding the highest values of SNRCT were found using thick filter of high atomic number, small iris and use of an X-ray attenuation equalisation filter design. The exposure limits make the CF interdependent, yielding another optimal setting. The CF setting was also found to be independent of the contrasting detail, in the particular case study.

  • 2. Hammersberg, P.
    et al.
    Stenström, Mats
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Sandborg, Michael
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    Matscheko, G.
    Alm Carlsson, Gudrun
    Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
    A theoretical model for determination of the optimal irradiation conditions for computerised tomography1995In: Insight (Northampton), ISSN 1354-2575, E-ISSN 1754-4904, Vol. 37, no 12, p. 978-985Article in journal (Refereed)
    Abstract [en]

    Image quality in Computerised Tomography (CT) depends strongly on the quality of the CT-projection data. These depend on sample composition and geometry, contrasting details within the sample and the equipment used, i.e. X-ray spectra, filtration, detector response and geometry. This paper focuses on the problem of selecting the optimal physical parameters to maximise the signal-to-noise in CT projection data (SNRCT) between a contrasting detail and the surrounding sample for CT-scanners equipped with poly-energetic X-ray sources (conventional X-ray tubes) and energy-integrating detector systems (image intensifier and optical video chain). The work includes the derivation and verification ofa theoretical model for SNRCT which can be used for predicting the optimal physical parameters for specific imaging tasks. It is shown that simplified calculations valid for mono-energetic X-ray sources and/or photon counting detectors do not correctly predict the optimal settings. This study also includes measurements of the actual X-ray source and photon transport Monte Carlo simulations of the response of the detector system.

  • 3.
    van den Bos, B
    et al.
    CSM Mat Teknik, S-58113 Linkoping, Sweden.
    Sahlen, S
    CSM Mat Teknik, S-58113 Linkoping, Sweden.
    Andersson, J
    Automatic scanning with multi-frequency eddy current on multilayered structures2001In: Insight (Northampton), ISSN 1354-2575, E-ISSN 1754-4904, Vol. 43, no 3, p. 163-166Article in journal (Refereed)
    Abstract [en]

    Eddy current testing is a frequently used NDT method at Saab/CSm but until recently only single frequency testing has bern used. Through the participation of Saab/CSM in a Brite-Euram project, 'CANDIA', it has been possible for Its to learn about multi-frequency testing and also to combine it with a flexible scanner developed in a preceding Brite-Euram project. The purpose of our work was to increase both testing speed and sensitivity ht: using multi-frequency eddy current testing, combined with a scanning system for corrosion detection in multi-layered structures. The wing of the Saab 2000 aircraft was one specific example for which several samples were manufactured with both artificial (chemically etched) corrosion of various severity and cracks. After optimising single frequencies, multi-frequency testing was adopted Using the previously determined optimal single frequency as a start, frequency combinations were determined to give increased detectability for the different structures and defects. The influence of different disturbing signals, for example signals from rivets, thickness variations, noise, and how to reduce them using the multi-frequency technique, was studied. A scanner was adapted to make it compatible with the eddy current instrument, resulting in a complete scanning system. During the project, tests were also made in 'field' conditions to evaluate the system. Components with real corrosion have also been tested with promising results. The possibility to produce scans from the mixed multi-frequency signals was very fruitful. The goals to increase testing speed and sensitivity have been reached. The combination of an advanced multi-frequency instrument with a scanning system will result in faster inspections and yield better results than could be achieved previously at Saab and CSM. These developments will increase the use of eddy current inspections.

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