When learning a foreign language, one needs to learn to work with new nouns and verbs. With MRI, one needs to learn a new Gray scale and new relationships between soft tissues. For instance on CT, cortical bone is always white, while on MRI it is always black. To complicate matters, where CT is absolute, MRI often provides relative relationships. CSF is always black on CT but with MRI can be gray or white depending upon the pulse sequence chosen.
Soft tissues have variable appearances based on the pulse sequences chosen.
If you are looking for absolutes in MR imaging, you will be disappointed. One needs to understand TR, TE, and flip angle relationships when performing imaging in the pulse sequence family known as field echo or gradient echo imaging. As an analogy, one can think of different dialects when trying to learn a foreign language. If you were attempting to learn Chinese, it would be important to know whether you are learning Mandarin or Cantonese or one of the other many dialects found in China. There is nothing analogous to this with plain film radiology or CT scanning.