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ASTM E746 Multi Hole Plates (and E1735) https://www.x-ray-forum.net/./22161106nx65772/iqi-image-quality-indicator-f91/astm-e746-multi-hole-plates-and-e1735-t47.html |
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Author: | Klaus [ 22.11.2019, 18:20 ] |
Post subject: | Re: ASTM E746 Multi Hole Plates (and E1735) |
Taking the images: For the exposure remove all filters or anything out of the beam - without the absorber plate and the plaques. To avoid unsharpness due to the size of the focal spot, the sourve detector distance (SDD) shall be a multiple of the focal spot size (FS). The absorber plate has to be placed directly on the detector, the plaques face the tube. For the steel plaques the SDD shall be 381*FS + 19mm but more than 1m. E.g. for a 1mm Focal Spot SDD shall be the larger value of (381*1mm+19mm =) 400mm and 1m - which is 1m. Hint: As long as your focal spot is <2.5mm the 1m distance is required. For the plastic plaques the SDD shall be 698*FS + 35mm but more than 1m. Hint: As long as your focal spot is <1.3mm the 1m distance is required. For the MeV version the 1m minimum is also valid but additionally the geometrical unsharpness Ug shall not be larger than 0.15mm. It can be calculated with Ug=FS(v-1) with v =magnification and would lead to a minimum value for the SDD of 1000*FS+150 [mm]. Both standards require that three exposures are done with identical settings. For digital systems the digital value (Pixel Value PV) shall be within 40% to 60% of max. PV. For DDA exposures it may be difficult to reach such a high value and it is not required because DDA systems have no dose limit; in this case other PV values can be selected when approved by the cognizant engineering authority. Same situation when using digital filters as shown in the post before. |
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