This is the term of MRI, T1T2 signal is related to the movement of H ion, the water content of human tissue is different, so the influence of magnetic field is different in MRI, let’s say cerebrospinal fluid is black signal on T1 scan sequence, T2 scan sequence is white, we say long t1 long t2. If black abnormal tissue signal is found on T1 sequence scan, it can be said to be long T1, if white abnormalities are found on T1, we say short T1 signal. It is similar for long T2 short T2.