In this paper we describe a technique for determining the modulation transfer function (MTF) of an imaging system from an experimentally obtained edge profile. The technique includes an exact correction for the frequency passband of the finite-element differentiation required to obtain the line spread function from the edge spread function. This correction has been ignored by investigators in the past and is required whenever finite-element differentiation is used rather than analytic differentiation of a model fitted to the edge response data. The magnitude of the MTF correction is approximately 11% at f = fc/2 and approximately 57% at f = fc, where fc = fs/2 is the maximum frequency reproducible without aliasing with a sampling rate of fs. The correction is performed in the spatial frequency domain by multiplying the uncorrected MTF by 1/sinc (pi f/2fc). A computer simulation is presented to demonstrate the effect and the correction procedure. An experimental MTF of an x-ray image intensifier system obtained using this technique is found to be consistent with an MTF obtained using a bar pattern test phantom.