: What does the intensity in an MR image represent? Hounsfield units are frequently used as intensity for CT images. What is used for MR images?

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There are no units for MRI intensity.

A Comparison of Five Methods for Signal Intensity Standardization in MRI (CEUR-WS.org):

A major problem in magnetic resonance imaging (MRI) is the lack of a
pulse sequence dependent standardized intensity scale like the
Hounsfield units in computed tomography.

MRI sequences (Radiopedia):

When describing most MRI sequences we refer to the shade of grey of
tissues or fluid with the word intensity, leading to the following
absolute terms:


high signal intensity = white
intermediate signal intensity = grey
low signal intensity = black


Often we refer to the appearance by relative terms:


hyperintense = brighter than the thing we are comparing it to
isointense = same brightness as the thing we are comparing it to
hypointense = darker than the thing we are comparing it to


Annoyingly these relative terms are used without reference to the tissue being used as the comparison.

See also: Signal intensity (MR-tip.com)