Evaluation of the susceptibility effect on the phase images of a simple gradient echo.

The phase shifts of a simple gradient echo (fast low-angle shot) were correlated with the local change in resonance frequency due to the differences in susceptibility among tissues (susceptibility effect). Susceptibility effects were considered theoretically, and the phase shifts for spherical and cylindrical configurations were calculated. A 1.5-T magnetic resonance unit and phantoms filled with solutions of copper chloride in water were used to obtain the phase images. The phase shifts of the simple gradient echo coincided with the values calculated with use of the sum of the macroscopic magnetic field and the cavity field of Lorentz. The authors conclude that the gap of the phase shifts at interfaces of tissues is useful in the evaluation of differences in magnetic susceptibility among tissues.