High-field fMRI

Abstract

Magnetic resonance imaging (MRI) allows detection of signal from constituent of biological tissues. Hydrogen (1H) is the most widely used element from which spectra and images are detected due to its abundance and high sensitivity manifested in its gyromagnetic ratio. The high contrast for soft tissue have afforded scientists invaluable information about brain structure and function. Among many parameters determining quality of MRI images, fi eld strength is the most decisive one as it determines signal strength in fMRI images. Considering the low inherent sensitivity of fMRI, high magnetic fi eld are the only way that activation contrast of neurofunctional studies could be increased. This is why there has been a relentless drive towards higher fi eld strength in human imaging raising it up to 11.7 T to date. Technology of 7-T has become more widely available in scanners with fMRI capability. Development of many technologies such as multichannel RF coils, strong and fast gradients, simultaneous slice excitation, and brainstimulation protocols have contributed to the expansion of fMRI as the method of choice for study of whole brain function. In this chapter, challenges of high-fi eld fMRI in human studies are discussed among which signal to noise, susceptibility artifacts, multichannel RF coil designs are highlighted.