MRI Basics Made Easy

Physics behind MRI has been explained here:

The strength of signal depends on proton density and two relaxation times T1 and T2. T1 depends on the time proton takes to return to axis of magnetic field and T2 is the time proton takes to dephase. Most of the pathological lesions show increased T1 and T2 relaxation times and therefore appear black of T1 and white on T2 weighted images.

MRI imaging can be done directly in any plane and soft tissue delineation is better but takes longer time than performing a CT scan.

Things that are bright on T1:

1. Fat – marrow and subcutaneous tissue
2. Blood
3. Contrast
4. Melanin
5. Protein-rich fluid

Things that are darker on T1:

1. Water – intermediate
2. Muscle – intermediate
3. Bone and fibrous tissue – dark
4. Air – very dark
5. Metal and hemosiderin
6. Fast moving blood in vessels

Things that are bright on T2:

1. Water
2. Edema
3. Tumor
4. Blood
5. Fat – if no fat suppression performed

Things that are dark on T2:

1. Bones and tendons
2. Metal and hemosiderin
3. Air
4. Fast moving blood in vessels