The integral dose to the patient and image signal to noise ratio (SNR) are inexorably coupled in x-ray-based diagnostic imaging. Advancements and optimal design of imaging devices need to consider the SNR as well as patient dose. The figure of merit, FOM=(SNR)2/(integral dose), is a useful parameter in optimizing detector designs because it is independent of input exposure, and therefore eliminates exposure as a design consideration. Although numerical calculation of the SNR is relatively straightforward in most cases, the integral dose calculation is made complex due to its scatter component's high dependency on both x-ray energy and patient thickness. Monte Carlo calculations over a range of monoenergetic x-ray energies were used to calculate total energy absorption, and the results are parametrized using polynomial expressions. The results are shown to be applicable to any arbitrary polyenergetic spectrum. An example using the above FOM is given to illustrate the utility of the parametrized results. The parametrized results may prove useful in the computer simulations of x-ray detector systems where the above FOM is utilized.
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