Recent Progress in MR Imaging of the Central Nervous System

MR imaging has become the modality of choice for neuroimaging. Long examination time was one of the clinical issues of MR imaging, especially for acquiring T2-weighted images with spin-echo sequence. However, MR system has progressed recently and new techniques have become available. The, use of segmented k-space method greatly facilitated reduction of the examination time. We can obtain T2-weighted images in a few minutes with this technique in combination with spin-echo sequence called "fast or turbo spin-echo (FSE or TSE)" imaging. In addition, fluid attenuated inversion recovery imaging (FLAIR) is now also clinically acceptable with the method. On ELAIR images, T2-elongated lesions are demonstrated more distinctly as hyperintense areas in contrast with hypointense cerebrospinal fluid (CSF). Constructive interference in steady state (CISS) imagining is a gradient-echo sequence. CSF and lymph in the inner ear are markedly hyperintense on CISS images. Because of thin sections (< 1 mm-thickness), thin nerves and vessels as well as inner ear structures are identified exactly on these images. Echo-planar imaging (EPI) is also clinically available. Diffusion-weighted images with EPI can demonstrate hyperacute infarction in a few seconds, which could not been detected with any other pulse sequences. Epidermoid cyst and brain abscess are markedly hyperintense on diffusion-weighted images. Therefore, diagnosis of the diseases is strongly supported with diffusion-weighted images. At present, MRI gives us not only Morphological information but also functional one of the brain