Magnetic susceptibility artifacts (or just susceptibility artifact) refer to a variety of MRI artifacts that share distortions or local signal change due to local magnetic field inhomogeneities from a variety of compounds.
They are especially encountered while imaging near metallic orthopedic hardware or dental work, and result from local magnetic field inhomogeneities introduced by the metallic object into the otherwise homogeneous external magnetic field B0. These local magnetic field inhomogeneities are a property of the object being imaged, rather than of the MRI unit.
A common susceptibility related artefact, deliberately sought to make small lesions more conspicuous, is the blooming artefact.
Types of magnetic susceptibility
In terms of magnetic susceptibility, most materials can be classified as diamagnetic, paramagnetic, superparamagnetic, or ferromagnetic.
Water is considered (weakly) diamagnetic.
Paramagnetic materials, which have unpaired electrons, concentrate local magnetic forces and thus increase the local magnetic field, i.e. have increased magnetic susceptibility.
Superparamagnetic materials contain particles with a much stronger magnetic susceptibility than that of paramagnetic materials, e.g. SPIO (superparamagnetic iron oxide) has been used in liver imaging.
Ferromagnetic materials contain large solid or crystalline aggregates of molecules with unpaired electrons exhibit “magnetic memory,” by which a lingering magnetic field is created after their exposure to an external magnetic field. Examples of ferromagnetic metals include iron, nickel, and cobalt, all of which distort magnetic fields, thereby causing severe artifacts on MR images.
- MRI (introduction)
- MR physics
- MR hardware
- signal processing
MRI pulse sequences (basics | abbreviations | parameters)
- spin echo sequences
- inversion recovery sequences
- gradient echo sequences
- fat-suppressed imaging sequences
- pulse sequence parameters
- diffusion weighted sequences (DWI)
- derived values
- CSF flow studies
- susceptibility weighted imaging (SWI)
- saturation recovery sequences
- echo-planar pulse sequences
- metal artifact reduction sequence
- T1 rho
- spiral pulse sequences
- MR angiography (and venography)
MR spectroscopy (MRS)
- Hunter's angle
- lactate peak: resonates at 1.3 ppm
- lipids peak: resonate at 1.3 ppm
- alanine peak: resonates at 1.48 ppm
- N-acetylaspartate (NAA) peak: resonates at 2.0
- glutamine-glutamate peak: resonate at 2.2-2.4 ppm
- gamma-aminobutyric acid (GABA) peak: resonate at 2.2-2.4 ppm
- 2-hydroxyglutarate peak: resonates at 2.25 ppm
- citrate peak: resonates 2.6 ppm
- creatine peak: resonates at 3.0 ppm
- choline peak: resonates at 3.2 ppm
- myo-inositol peak: resonates at 3.5 ppm
- functional MRI
- MR hardware and room shielding
- MR software
- patient and physiologic motion
- tissue heterogeneity and foreign bodies
- Fourier transform and Nyqvist sampling theorem
MR contrast agents
- gadolinium ion
- extracellular MRI contrast agents
- hepatobiliary MRI contrast agents
- intravascular (blood pool) MRI contrast agents
- gastrointestinal MRI contrast agents
- tumor-specific MRI contrast agents
- reticuloendothelial MRI contrast agents
- contrast agent safety
- MR safety
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