Room: AAPM ePoster Library
Purpose: objective of this study is to determine the most efficient ratio of anti-scatter-Grid, generally used in a digital radiography (DR) system, by comparing image quality indicators and to optimize specification of anti-scatter-Grid for As Low As Reasonably Achievable (ALARA) principle.
Methods: use stacks of poly methyl methacrylate (PMMA) plates as a phantom to generate different scatter fraction by changing height of the stacks. And image acquisition process is performed at 100kV of tube voltage using 140 µm pixel size of detector for modulation transfer function (MTF), normalized noise power spectrum (NNPS) and scatter fraction (SF), which are used to calculate effective detective quantum efficiency (eDQE) and effective noise equivalent quantum (eNEQ). These image quality indicators, for a given thickness of PMMA stacks, exposure level and Grid ratio, are used to determine which ratio is the most efficient for anti-scatter-Grid in terms of ALARA principle.
Results: results show that image quality related with resolution is increased as higher Grid ratio, not depending on exposure level. And from NNPS results, we can see that Grid intrinsic noise affect more to image quality at high exposure level, but quantum noise become the most dominant noise source at over 10m thickness of PMMA stacks eventually. In eDQE and eNEQ results, high Grid ratio is always more efficient than low Grid ratio. Especially, as an example case of PMMA 20 cm, efficiency of 15 ratio Grid at given exposure can be comparable with that of 6 ratio Grid at 3 times higher exposure level.
Conclusion: a high ratio Grid can absorb more photons than a low ratio Grid, the image quality efficiency is increased as higher Grid ratio and also this fact can be used to achieve ARALA principle.