CHAPTER 4: Ultra-high Field Imaging

MR spectroscopy (MRS) reveals information about the molecular structures underlying the MR signal. Properties such as chemical shift and scalar coupling cause a characteristic splitting of the resonance frequencies and following the numerical fitting of the acquired data to the corresponding basis spectra, these shifts can be used to distinguish different kinds of molecules. For in vivo applications, spatial localisation techniques for signal acquisition, such as STEAM or PRESS, and water signal suppression, i.e. CHESS or MEGA, are required. Using non-proton nuclei as target nuclei allows MRI to investigate in vivo metabolic processes and pathology non-invasively. These so-called X-nuclei impose increased technological and methodological demands, as the sensitivity and abundance are significantly lower compared to protons and their spin dynamics might be more sophisticated and complex. Nevertheless, the potential benefit of acquiring such data is tremendous both clinically and in research. The most prominent X-nuclei in vivo are ²H, ⁷Li, ¹³C, ¹⁷O, ¹⁹F, ²³Na, ³¹P, ³⁵Cl and ³⁹K and a subset are discussed here. One of the applications that constitutes a ‘perfect fit’ for ultra-high field imaging is the depiction of brain anatomy. The usual challenges of ultra-high field imaging pertain but once overcome anatomical imaging of the brain is able to produce in vivo images with unprecedented resolution and contrast. The chapter concludes with a brief excursion into ‘emerging applications’ and includes phase and susceptibility imaging, quantitative susceptibility imaging and CEST-based imaging at ultra-high field.