MR imaging of susceptibility-induced magnetic field inhomogeneities.

Abstract

A 90 degrees-tau 1-90 degrees-tau 2-image acquisition pulse sequence allows spatial mapping of resonant frequency. This sort of sequence has previously been used for magnet shimming, and its use in chemical-shift imaging has been proposed. The authors used this sequence in magnetic resonance imaging of a phantom to demonstrate the magnetic field gradients arising from susceptibility differences within the phantom and allow those gradients to be measured. Gradients may arise near interfaces between substances that cannot support the same magnetic flux density. The pulse sequence was found to work well in lower-field-strength instruments.

Metal-related artifacts in instrumented spine. Techniques for reducing artifacts in CT and MRI: state of the art

“…MRI degradation caused by metal hardware is primarily the result of a series of MRI artifacts produced by the ferromagnetic properties of the metallic device [22]). These artifacts include intravoxel dephasing, diffusion-related signal loss, slice thickness variation, misregistration artifacts, and inhomogeneous or paradoxical tissue-selective signal suppression with spectral (frequency-selective) fatsaturation techniques.…”

Functional cerebral imaging by susceptibility‐contrast NMR

“…These substances, which include transition and lanthanide metal ions, produce relaxivity effects through dipole-dipole interactions between their unpaired electron spins and the nuclear spin (21). They can also influence the bulk magnetic susceptibility of a sample (22)(23)(24)(25). In tissue, relaxivity effects have been studied in detail; however, changes in the microscopic magnetic field distribution due to compartmentalized high-magnetic moment agents have only recently been investigated (26)(27)(28)(29).…”

Magnetic resonance imaging of the postoperative hip

“…Magnetic susceptibility refers to the tendency of a substance to become magnetized when exposed to an external magnetic field (7). The degree to which a material is magnetized is proportional to the applied magnetic field (B 0 ) and the susceptibility constant of the material being imaged.…”

“…The effect is one of mismapping of the object in the frequency-and slice-encoding directions, producing regions of not only high signal intensity, but also regions of signal loss within the image (7,8). Misregistration artifact is therefore most conspicuous in the frequency-encoding direction (9).…”