Computing the modulation transfer function of a magnetic resonance imager.

A new method for computing the modulation transfer function (MTF) of magnetic resonance (MR) imagers is presented. Previous attempts to compute the MTF of MR images used nonlinear magnitude reconstructed images, resulting in erroneous MTFs. By using complex domain images, the new method produces predisplay MTFs which describe the spatial frequency transfer characteristics of the entire image formation process, except the magnitude operator, eliminating the artifacts previously found in MR imager MTFs. The use of complex domain images results in two-sided MTFs which differentiate the positive and negative frequencies associated with positive and negative phase encoding or positive and negative time relative to the echo formation. Experimental results are presented which confirm the theoretically predicted form of MR imager MTFs and the need for two-sided MTFs.