Magnetic resonance imaging (MRI) is a non-invasive imaging technique used in hospitals and clinics to produce detailed soft tissue anatomical images through emission and absorption of energy of the radiofrequency range of the electromagnetic field by employing powerful magnets that produce a strong magnetic field around the area to be imaged without exposing the body to ionized radiation.
Some medical conditions require a contrast or a difference in signal intensity between them and the adjacent tissue to be visible in an MRI scan. MRI scans have intrinsic contrasts (sequences), in terms of electromagnetic properties (radiofrequency pulses and gradients) and their modification, which results in a set of images with a particular appearance. The basic sequences are T1-weighted (where fat has a high signal intensity and is seen as white; water has a low signal intensity and is seen as black) and T2-weighted (where water has a high signal intensity and is seen as white).
In certain cases, the intrinsic differences (sequences) are not enough to achieve the desired degree of contrast, so contrast agents are added to introduce additional differences. These agents are paramagnetic chemicals and they reach certain tissues/fluids, artificially changing their electromagnetic properties. Gadolinium-based contrast agents are the most used worldwide and the general indications for their use include lesion identification (lesions in some parts of the brain like the cerebellopontine angle and sellar/parasellar regions, metastasis and demyelinating lesions) and characterization (differentiating a tumor from inflammation or an infection; vascularity of some lesions).
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