It is a term used in MRI imaging to describe the lesions imaged on MRI. A long T1 signal is a low signal that appears as a very dark signal on cranial MRI. A long T2 signal is a high signal and appears as a very bright signal on cranial MRI. The long T1 and long T2 signal found on top of the cranial MRI should first be considered as a demyelinating lesion of the nerve conduction tract of the brain. This condition is mostly seen in multiple sclerosis, optic neuromyelitis optica, and many intracranial tumors also have such demyelinating changes, which need to be further identified by cranial MRI with enhancement scan.