MRI image appearance

The easiest way to identify proton density (PD) fat saturated images is to look for adipose tissues in the body (e.g. subcutaneous fat and fat in bone marrow). Areas contain adipose tissues appear as dark on PD fat saturated images. All other characteristics of the PD fat saturated images remain same as the PD image.

Tissues and their PD fat saturated images appearance

Bone marrow: - dark
Muscles- gray
Fat – dark
Fluids – bright   
White matter - darker than bright gray
Gray matter - bright gray
Moving blood- dark
Bone - dark
Air - dark 

Pathological appearance

Pathologies with adipose tissues content will appear as dark in PD fat saturated images (e.g. lipoma). Due to the added fat suppression, pathological processes are usually  bright on PD  fat saturated images.

Very useful for extremity imaging (e.g. ankle, knee, elbow shoulder and hips)
Can be useful in thighs, lower legs, upper arms and forearms imaging


PD fat sat axial sequence used knee   imaging

PD fat sat coronal sequence used ankle imaging