We evaluate a new method for measuring the presampled modulation transfer function (MTF) using the noise power
spectrum (NPS) obtained from a few flat-field images acquired at one exposure level. The NPS is the sum of structure,
quantum, and additive instrumentation noise, which are proportional to exposure squared, exposure, and a constant,
respectively, with the spatial-frequency dependence of the quantum noise depending partly on the detector MTF.
Cascaded linear-systems theory was used to derive an exact and generic relationship that was used to isolate noise terms
and enable determination of the MTF directly from the noise response, thereby circumventing the need for precision test
objects (slit, edge, etc.) as required by standard techniques. Isolation of the quantum NPS by fitting the total NPS versus
exposure obtained using 30 flat-field images each at six or more different exposure levels with a linear regression
provides highly accurate MTFs. A subset of these images from indirect digital detectors was used to investigate the
accuracy of measuring the MTF from 30 or fewer flat-field images obtained at a single exposure level. Analyzing as few
as two images acquired at a single exposure resulted in no observable systematic error. Increasing the number of images
analyzed resulted in an increase in accuracy. Fifteen images provided comparable accuracy with the most rigorous slope
approach, with less than 5% variability, suggesting additional image acquisitions may be unnecessary. Reducing the
number of images acquired for the noise response method further simplifies and facilitates routine MTF measurements.