| Popis: |
A general model for the quantitation of spin-echo and gradient-echo artifacts in samples with macroscopic susceptibility inhomogeneities is developed. Its usefulness is tested by comparing experimental images and computer simulations of cylindrical susceptibility inhomogeneities. Positional displacements, gradient-echo phase shifts, and diffusion and sampling time effects, which are responsible for local image distortions and signal losses, are calculated on a subpixel basis to provide a quantitative comparison of susceptibility artifacts under various imaging conditions. The formulation will be useful for the interpretation of susceptibility-related signal losses in gradient-echo imaging and for the analysis of spin-echo susceptibility artifacts at high field strengths. In addition susceptibility effects in NMR microscopy and contrast properties of particulate contrast agents may be simulated. |
