Purpose: to present a new and simplified method for pixel-wise determination of the signal-to-noise ratio improvement factor KSNR of an antiscatter grid, when used with a digital imaging system. The method was based on approximations of published formulas. The simplified estimate of K(2)SNR may be used as a decision tool for whether or not to use an antiscatter grid.
Methods: the primary transmission of the grid Tp was determined with and without a phantom present using a pattern of beam stops. The Bucky factor B was measured with and without a phantom present. Hence K(2)SNR maps were created based on Tp and B. A formula was developed to calculate K(2)SNR from the measured Bs without using the measured Tp. The formula was applied on two exposures of anthropomorphic phantoms, adult legs and baby chest, and on two homogeneous poly[methyl methacrylate] (PMMA) phantoms, 5 cm and 10 cm thick. The results from anthropomorphic phantoms were compared to those based on the beam stop method. The results for the PMMA-phantoms were compared to a study that used a contrast-detail phantom.
Results: 2D maps of K(2)SNR over the entire adult legs and baby chest phantoms were created. The maps indicate that it is advantageous to use the antiscatter grid for imaging of the adult legs. For baby chest imaging the antiscatter grid is not recommended if only the lung regions are of interest.The K(2)SNR maps based on the new method correspond to those from the beam stop method, and the K(2)SNR from the homogenous phantoms arising from two different approaches also agreed well with each other.
Conclusion: a method to measure 2D K(2)SNR associated with grid use in digital radiography system was developed and validated. The proposed method requires four exposures and use of a simple formula. It is fast and provides adequate estimates for K(2)SNR.