Short T1 and long T2 refers to the signal of the lesion shown in T1 and T2 sequences during MRI. Short T1 is high signal in white, and long T2 is also high signal in white. For example, when a brain hemorrhage is 8 days-4 weeks old, the hematoma MRI image shows a short T1 and long T2 signal, but in the hyperacute phase (i.e., within 24 hours of hemorrhage) and chronic phase (more than 4 weeks of disease), the hematoma is a long T1 and long T2 signal. In magnetic resonance T1 is longitudinal relaxation and T2 is transverse relaxation, the black and white contrast of magnetic resonance originates from the difference of magnetic resonance signal of various tissues. tissues with short T1 (such as fat) produce high signal in white color, called short T1, such as fluid, tumor, infarct foci and inflammation are low signal in T1 sequence, which is black, then it is called long T1 signal; but in T2 sequence is high signal in white color, called long T2 signal.