Transfer function measurement and analysis for a magnetic resonance imager

The transfer function characteristics of a 1.5T imager have been determined. An edge response function (ERF) was obtained from a water/Plexiglas interface at various pixel widths ranging from 0.312 to 1.0 mm. An SE pulse sequence was used with a 5-mm transaxial slice. The ERF was smoothed, differentiated, and Fourier transformed to obtain MTF curves. The LSF was analyzed for skewness and kurtosis. The area under the MTF amplitude curves and the equivalent bandpass were calculated. All ERFs, LSFs, and MTFs were well behaved. The resulting LSF was Gaussian. All calculated MTFs had cutoff frequencies slightly less than the theoretical Nyquist limit. The MTF calculated from the theoretical Gaussian LSF is slightly superior to that calculated from experimental data and provides an upper limit to the MTF. Spatial resolution in our MR imager is dominated by the pixel size via the Nyquist sampling theorem. System performance is slightly less than theoretically predicted, possibly due to image processing algorithms during the reconstruction process.