A century after the discovery of X-rays, the low-energy range of the electromagnetic spectrum also attained broad application in radiology. Radiofrequency waves allow excitation in a magnetic field of the magnetic resonance of spin-bearing nuclei in tissue. Using the intense signal of the water protons, morphological images of the human body can be obtained, while at a higher frequency resolution also endogenous metabolites as well as pharmaceuticals, which contain MR-visible nuclei (e.g., 1H, 13C, 19F, 31P), can be detected noninvasively and in vivo. Accordingly, in vivo MR spectroscopy is a technique which is sensitive to molecules and molecular properties and which can be applied to repeated examinations. Its major limitation is the low signal intensity vs noise, which implies long measurement times and poor spatial resolution. Using spectroscopic imaging, the distribution of metabolites within an organ can be monitored selectively and displayed as a molecular image.