Theory and application of static field inhomogeneity effects in gradient‐echo imaging

Abstract

The influence of local static magnetic field inhomogeneities on gradient-echo imaging is discussed and the underlying theoretical aspects are reviewed. A high-resolution approach is suggested to suppress image distortion and restore signal loss due to spin dephasing. Acquisition of three-dimensional data sets not only overcomes part of the limitations associated with gradient echoes but also makes it possible to extract local information about the strength or direction of background gradients and relative susceptibility changes between different tissues. Applications of the suggested approach in the human brain for anatomical imaging as well as for extraction of physical and physiological parameters are presented and discussed.

Determination of brain iron content in patients with Parkinson’s disease using magnetic susceptibility imaging

“…For most configurations, it will create local magnetic fields that vary spatially outside of its inner core, leading to signal dephasing. Irrespective of the diamagnetic or paramagnetic property of the sources, changes in the local magnetic field lead to spatial variations in phase outside the source, and therefore, to the dephasing of the signal and a reduction in T2* [18] . The amount of dephasing does not depend on whether the material is paramagnetic or diamagnetic, but on the field variations across a voxel.…”

Susceptibility‐weighted imaging to visualize blood products and improve tumor contrast in the study of brain masses

“…To enhance the visibility of the venous structures, the magnitude images were multiplied four times with a phase mask generated from the filtered phase data (22). This postprocessing was automatically done by a modified version of the spectrometer software in 33 cases.…”

Different Iron-Deposition Patterns of Multiple System Atrophy with Predominant Parkinsonism and Idiopathetic Parkinson Diseases Demonstrated by Phase-Corrected Susceptibility-Weighted Imaging

“…Moreover, phase images can enhance contrast to local changes in magnetic susceptibility, therefore, yielding increased sensitivity in detecting local changes in iron content. [24][25][26] Nonheme iron, usually in the form of ferritin, is a highly paramagnetic molecule, which causes a phase shift in the local field correlated with the amount of iron deposition. 25,27 We believe that SWI would be a very sensitive imaging sequence, better elaborating putative iron distribution or extent in the deep gray nuclei of patients with MSA-P and IPD.…”