Frequency shift artifacts in MR imaging

Chemical shifts may be expressed as distortions and displacements in magnetic resonance (MR) images. Specifically, in two-dimensional Fourier transform reconstructions such shifts produce visible displacements in the direction of frequency encoding. This is readily observable at 0.26 T with phantoms comprised of in vitro solutions with known chemical shifts and human tissues with disparate fat content. Moreover, frequency shift artifacts are visible in routine abdominal scanning at the interfaces of structures of differing fat content. Two common examples of this involve the vertebral body and intervertebral disk and the kidney and surrounding retroperitoneal fat. Without appropriate changes in gradients, such distortions may be expected to increase with increasing magnetic field strength.