The future of ultra-high field MRI and fMRI for study of the human brain

Abstract

MRI and fMRI have been used for about three and two decades respectively and much has changed over this time period, both in the quality of the data and in the range of applications for studying the brain. Apart from resolution improvements from around 4mm in the early days to below 0.5mm with modern technology, novel uses of contrast have led to the ability to sensitize images to some of the brain's structural properties at the cellular scale as well as study the localization and organization of brain function at the level of cortical columns. These developments have in part been facilitated by a continuing drive to increase the magnetic field strength. Will the next few decades see similar improvements? Here we will discuss current state of high field MRI, expected further increases in field strength, and improvements expected with these increases.

Fig. 1

Dependence of relaxation rates, SNR, and CNR on field strength B. (a) relaxation rate R₁ and R₂* as function of field strength according to Eqs. (1a) and (1b) respectively. (b) SNR and CNR as function of B. CNR increases faster than SNR by a factor ΔR₂*/R₂*, which is graphed in (c). Both tend to a square root dependency on B in the high field limit. Quantities in (b) and (c) are normalized to the values at B=1 T.