PSIR stands for Phase Sensitive Inversion Recovery and is typically used to improve the delineation of gray and white matter. In addition, the sequence provides high contrast-to-noise ratio (CNR) between MS lesions and normal tissue. TI value of PSIR sequence is selected at 350-600 ms.
PSIR sequence is useful for depicting cortical grey matter lesions (common in MS), which are usually not well visible on the other series, and shows great potential in revealing MS lesions in the cervical spinal cord (figure). Images courtesy of Bac Nguyen.