T1 and T2 stand for T1-weighted image and T2-weighted image, which is a descriptive term for imaging examinations, and its changes represent changes in normal as well as diseased tissues. A long T1 signal refers to a low signal on a T1-weighted image as a black image, while a long T2 signal refers to a high signal on a T2-weighted image, which appears as a white image. By already being very familiar with normal tissues and their signal changes, the imaging physician identifies disease when abnormal tissues are present, describing how a change in T1WI and T2WI signal appears in a certain location. A variety of diseases have different signal characteristics, such as occupancy showing a long T1 and long T2 signal shadow, and bleeding showing a short T1 and long T2 double high signal shadow, so different diseases have different signal characteristics of different diseases.