Purpose:To study the frequency response characteristic of the MRI signal receiver system as a contributing factor to the formation of Nyquist ghosting in echo-planar imaging (EPI). Materials and Methods:Experimental work was undertaken on a 1.5 T system. A cylindrical test object filled with water was imaged axially with EPI in the center of the quadrature, transmit-receive head coil. In the first set of experiments, the water conductivity was increased progressively with the addition of salt between EPI acquisitions. In the second set of experiments, the conductivity of the water in the test object was kept constant and EPI images were acquired at several different bandwidths. A computer simulation was also implemented to demonstrate the impact of changes in the frequency response characteristic of the signal receiver system on EPI Nyquist ghosting.Results: Experimental and simulation results showed that Nyquist ghosting increased with the variation of the frequency response characteristic within the effective frequency range determined by the image bandwidth. One can increase the variation in the frequency response characteristic by increasing its steepness over the image's bandwidth window when coil loading is decreased, or by increasing the effective frequency range when image bandwidth is increased. Conclusions:The results of this research may help reduce Nyquist ghosting in EPI studies when the imaging coil is not sufficiently loaded, such as in pediatric and phantom studies. ECHO-PLANAR IMAGING (EPI) is susceptible toNyquist ghosting because of the bipolar frequency-encode gradients implemented in the EPI sequence. The MRI signal is reversed in k-space when it is recorded under a negative frequency-encode gradient. As a consequence, any modulation or discrepancy in the MRI signal becomes antisymmetric with respect to the center of the acquisition window, between successive kspace lines. The resulting discontinuity between even and odd k-space lines gives rise to Nyquist ghosting. Several sources of MRI signal interference have been identified as contributing factors in EPI Nyquist ghosting, such as eddy currents, concomitant fields, oblique imaging, image filters, imperfect pulse sequence timing, B 0 field inhomogeneity, susceptibility differences, and chemical shift (1-4). In this work, the influence of the frequency response characteristic of the MRI signal receiver system on the formation of Nyquist ghosting in EPI is demonstrated using theoretical analysis and experimental data. We showed that Nyquist ghosting depends on the frequency response characteristic by changing the receiver coil loading and the image bandwidth. To confirm these results, a computer simulation was implemented to demonstrate the effect of changes in the frequency response characteristic of the MRI signal receiver system.Previous studies have identified the role of the receiver system in image quality with regard to signal intensity and uniformity (5,6). In this work we analyzed the effect of the receiver system on an additional...