Part 2 book “Advanced MR neuroimaging” has contents: Magnetic resonance spectroscopy, artifacts and pitfalls of MRS, functional magnetic resonance imaging (fMRI), artifacts and pitfalls of fMRI, the role of multiparametric MR imaging - advanced MR techniques in the assessment of cerebral tumors. | 5 Magnetic Resonance Spectroscopy Introduction Focus Point • MRS can be considered as a bridge between the anatomic and physiological information and the metabolic characteristics of tissue in vivo. • The principal phenomenon of MRS is the “chemical shift,” which is directly related to the biochemical environment of every nucleus. • The proton nucleus is the most useful nucleus for MRS, due to its high natural abundance (>) and intrinsic sensitivity (high gyromagnetic ratio γ). Magnetic resonance spectroscopy (MRS) is a technique which provides a non-invasive method for characterizing the cellular biochemistry of brain pathologies, as well as for monitoring the biochemical changes after treatment in vivo. In that sense, it can be considered a bridge between the anatomical and physiological information and the metabolic characteristics of tissue in vivo (Soares and Law, 2009). The principal phenomenon is the so-called “chemical shift,” which is caused by the unique (for every nucleus) shielding from the external magnetic field (B0) by the electrons surrounding them. Hence, this chemical shift effect is directly related to the biochemical environment of the nuclei. The electron magnetic moment opposes the primary applied magnetic field B0; therefore, the more the electrons the less the magnetic field the nuclei will “feel.” This “feeling” can be expressed as the effective magnetic field Bn of the nucleus: Bn = B0 (1−σ) () where σ, is the screening constant, which is proportional to the chemical environment of the nucleus. Hence, in vivo MRS is a combination of MR imaging and chemical spectroscopy, where instead of an image, a spectrum of resonant peaks is produced. Due to the chemical shift phenomenon, it is evident that MRS is feasible on any nucleus possessing a magnetic moment, such as a proton (1H), carbon-13 (13C), phosphorus (31P), and sodium (23Na). Early MRS studies were focused on the phosphorus nucleus (31P) since this was the .
