Evaluation of Spatial Frequency

A method was developed to accurately measure signal-to-noise ratios (SNRs) in positive and negative frequencies of magnetic resonance images (MRIs). SNR2(f) was calcu- lated from the modulation transfer function (MTF) and the Wiener spectrum, both of which were determined with subtracted complex images at the same phantom setting. The SNR2(f)s in the conventional spin echo (SE) and Turbo SE which set effective echo time at the first echo were evaluated by changing the T2 of the phantom in the frequency and phase encode directions. SNR2s gave positive and negative spatial frequency information that was not ob- tained with conventional methods. In this method, the influences of image nonuniformity and unnecessary artifacts could be eliminated. Analysis of the SNR in the spatial frequency do- main made it possible to obtain more detail on the image quality of MRI.