Ultra-High Contrast MRI of the Brain and Spinal Cord using Directly Acquired and Synthetic BipoLAr Inversion Recovery (BLAIR) Images

Ultra-high contrast (UHC) MRI is a term used to describe MR imaging that shows abnormalities with high contrast when little or no abnormality is seen on common conventional state-of-the-art MR images. It is achieved without the use of increased static or gradient magnetic fields. UHC can be accomplished by using tissue properties such as T1 and T2 twice or more in the same sequence. This synergistically contributes to overall contrast as with directly acquired divided subtracted inversion recovery (dSIR) T1-BipoLAr Inversion Recovery (BLAIR) sequences. These sequences can also provide high contrast and high spatial resolution signal boundaries. UHC MRI can also be achieved by applying synthetic bipolar filters to high quality tissue property maps. Illustrative cases of mild traumatic brain injury, multiple sclerosis, methamphetamine substance use disorder, Parkinson's disease and white matter changes associated with a cerebral tumour are shown. Patients showed widespread abnormalities with directly acquired and synthetic dSIR and other BLAIR images in areas where little or no abnormality was seen on conventional T2-w spin echo and/or T2-FLAIR images. New signs seen on BLAIR images include the whiteout sign and grayout signs as well as the bilaminar cortex and bubble signs. dSIR and other BLAIR sequences create high contrast from small changes in T1 as well as other tissue properties, and are complementary to conventional clinical sequences which create high contrast from larger changes in T1 and/or T2. Comparison is made with other sequences which use single or combined inversion recovery images. Four types of BLAIR sequences are described. They utilise sequences that already exist on most MR machines and are easy to implement.