The extent to which a material or tissue becomes magnetized in an external magnetic field is called?

The correct answer is magnetic susceptibility. This term refers to the degree to which a material, including biological tissues, can be magnetized when an external magnetic field is applied. Magnetic susceptibility is a key concept in MRI because it affects how different tissues respond to the magnetic field and therefore influences image contrast and resolution.

In the context of MRI, tissues with different magnetic susceptibilities will appear differently on the scans due to variations in how they interact with the magnetic field. For instance, tissues with high magnetic susceptibility (such as those containing more iron) will behave differently compared to those with low susceptibility, which can enhance or diminish signals in the MRI images.

Understanding magnetic susceptibility is crucial for interpreting MRI images accurately and for designing imaging protocols that capitalize on these differences in tissue response. This concept is distinct from other terms like contrast to noise ratio and signal to noise ratio, which focus on the quality of the images rather than the interaction of materials with magnetic fields.