Guidewires are mostly used to guide catheters. Standard guidewires used in interventional X-ray are passive devices made from conductive materials, mostly metals. They are easily visualized in X-ray projections and CT by their radio-opacity due to metal contents. Active guidewires are important as well in clinical practice. The use of active guidewires for measurement of pressure, temperature, and flow is common in interventional X-ray.
In magnetic resonance imaging, a large magnetic field is used to align the nuclear spins of atoms as part of the procedure for producing images within the body of a subject. Magnetic resonance imaging is typically used to map the location of protons, such as those in a water molecule, within a subject. Magnetic resonance imaging is much better than X-ray techniques such as CT at imaging soft tissues and showing the detailed anatomical structures of soft tissues. However, the large magnetic field and radio-frequency signals used for magnetic resonance imaging prevents the use of some materials and electronics during a magnetic resonance imaging scan.