PIRADS: Having the same intensity as a reference tissue/structure to which it is compared.
[PIRADS] Intensity at MRI that is identical or nearly identical to that of a prostate.
LIRADS: signal is the same as the signal from the tissue to which it is compared (e.g., isointense to muscle)
[LIRADS] intensity at MRI that is identical or nearly identical to that of liver parenchyma.