The effects of scattered radiation from a semitransparent edge on MTF measurement: verification of several factors by Monte Carlo simulation

Accurate evaluation of image quality not only characterizes system performance but also allows quantitative understanding of various image quality factors and the resulting image quality changes. The presampled modulation transfer function (MTF) can be useful in determining system resolution characteristics and response reduction caused by certain image quality factors. Although many studies have been conducted to accurately measure the MTF, there is still ample room for investigation of factors that affect the measured MTF for a task-based assessment using a semitransparent edge. In this study, we focus on the effects of scattered radiation from the edge on MTF measurement. The edge enhancement effect confirmed by a previous study is verified using Monte Carlo simulation; influences on the MTF due to air gaps and scattered radiation from objects are investigated. This effect by scattered radiation from an edge is also confirmed in our simulation. The results show that as air gaps change, the effect on the MTF also changes; that is, as air gaps increase, the MTF peak shifts to lower spatial frequencies. When scatter is introduced by adding an object, the MTF obtained using a semitransparent edge in the low spatial frequency is higher than that of the opaque edges for RQA9. Thus, when using such an edge, the X-ray energy should be set such that the K absorption edge of the edge material is not exceeded. Further the experimental geometry, such as air gaps, and the effect of low spatial frequency due to scattered radiation should be considered.