WE‐C‐304A‐07: A Method for Measuring the MTF of Digital Radiography Systems Using Noise Response

Purpose: To provide a new method for measurement of the modulation transfer function (MTF) using the noise response of digital radiography systems. Method and Materials: Cascaded linear system methods have been used for several decades to accurately predict the signal and noise performance of a wide variety of digital x‐ray imaging technologies including x‐ray image intensifiers, direct and indirect flat‐panel detectors (FPDs), and CCD/EMCCD‐based detectors. The noise response of such imagers inherently incorporates the detector resolution response, i.e. the detector MTF. In this work, a generalized linear systems analysis was used to derive an exact relationship. The two‐dimensional noise power spectrum (NPS) was plotted versus the mean signal level, for all spatial‐frequencies. A linear regression was fitted to this data to isolate the quantum‐noise component, the shape of which depends in part on the system resolution. The spatial‐frequency response of the resulting slopes was then used to obtain the MTF. The accuracy of this method was investigated using simulated images from a simple detector model, based on high‐resolution EMCCD detectors, in which the MTF was known exactly. Measurements were also done on a FPD and the results were compared using the standard edge response method. Results: The MTF measured from the noise response of the simulated detector system showed exceptional agreement with the “true MTF” at both low and high spatial‐frequencies. Differences of 0.3%, 1.8% and 6.1% were observed at 5, 10 and 15cycles/mm, respectively. The FPD MTF obtained using the noise and edge response methods were also shown to agree within experimental uncertainty. Conclusions: Initial results indicate that the noise response method is a simple technique which can be used to accurately measure the MTF (in all directions simultaneously) of digital x‐ray imagers, alleviating the burdens of development and implementation of precision edge or slit devices. (Support: NIH‐R01‐EB008425; NIH‐R01‐EB002873).