NDTnet 1998 Aug, Vol.3 No.8

Abstract

Detectability in CT-images is the viewers' possibility to distinguish a detail or defect in a surrounding material. Detectability depends on the CT image quality, determined by the information transferred by X-rays penetrating the imaged sample and also the sensitivity and resolution of the imaging equipment.

Image quality can be described with contrast, resolution and noise. The contrast is the signal difference between a detail and surrounding material and depends on the difference in object and detail compositions and densities, and also the X-ray energy. The noise is defined as the standard deviation of the pixel-to-pixel variation. The signal-to-noise ratio, SNR, is the quotient of contrast and noise.

The range of variation of industrial objects (material and geometry) requires effective methods to predict the optimal settings to obtain maximal detectability in an imaging task. To determine the optimal system settings we have developed a calculation method based on the knowledge of the energy-spectra generated by the X-ray source and the response of the X-ray detector used. Functionality incorporated in the calculation method were:

• Prediction of optimal X-ray tube potential and energy-spectra pre-filtration for maximum SNR between defect and surrounding material.
• Determination of minimum detectable size of a certain specified defect within an object material as function of object diameter by using the imaging system modulation-transferfunction, MTF (i.e. resolution).
• Correction of beam-hardening artefacts for homogenous materials.
The proposed method has a variety of applications. It can be used to determine, in advance, if CT-inspection can be used as a NDE method for a specific task or as a tool to estimate CTsystem performance.
The validity and versatility of the method is shown in a number of imaging cases.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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