7 September 2006 Scintillator to CCD coupling in x-ray microtomography
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Optical coupling between the X-ray scintillator and digital camera (typically CCD) is a major design consideration in X-ray microtomography. Previously, we used a pair of 50mm f1.2 lenses, which we determined to be approximately 60 % efficient, that is, the signal to noise ratio is that which would occur if 60 % of the X-ray photons absorbed by the scintillator were directly detected. For larger CCDs, lenses become excessively large, heavy and expensive. For our 60 x 60 mm time-delay integration CCD camera, we used parallel fibre-optic coupling, giving greater efficiency. A problem with this is the scattering of light through the fibre cladding, which reduces image contrast, adding a very blurred image to the sharp image transmitted through the fibres. This problem is ideally suited to solution by deconvolution. Since the high frequency image components are present (direct fibre image) deconvolution can be used to eliminate the low frequency scatter image, without the problems normally associated with de-blurring. The point spread function was assumed to be rotationally symmetrical and was determined from an edge image of a lead plate positioned close to the scintillator. In frequency space, the mid frequency portion was extrapolated into the low frequency portion using a parabolic fit. The difference between the extrapolated and measured low frequency portions was deemed to be the scatter response. This was then added to the frequency response for a perfect delta function to obtain the frequency response used for deconvolution. The results showed excellent correction of the X-ray microtomographic images.
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Graham R. Davis, Graham R. Davis, James C. Elliott, James C. Elliott, } "Scintillator to CCD coupling in x-ray microtomography", Proc. SPIE 6318, Developments in X-Ray Tomography V, 631817 (7 September 2006); doi: 10.1117/12.679407; https://doi.org/10.1117/12.679407

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