Magnetic resonance imaging and spectroscopy of low concentration solutes with exchangeable protons using label transfer modules: frequency transfer, inversion transfer, and dephasing transfer

Abstract

An embodiment of the current invention provides a method for magnetic resonance (MR) imaging or spectroscopy, comprising: (a) selectively exciting exchangeable solute protons or protons of exchangeable solute-based water molecules within a frequency range in a subject using at least one frequency-selective radio frequency (RF) pulse, wherein the frequency range encompasses characteristic resonance frequencies of the exchangeable solute protons or protons of exchangeable solute-based water molecules, wherein the frequency range is substantially non-overlapping with a characteristic resonance frequency of bulk water protons in the subject, wherein the at least one frequency selective RF pulse performs a substantially minimal excitation on the bulk water protons, and wherein the at least one frequency-selective RF pulse, sometimes in combination with a time period that separates the at least one frequency-selective RF pulse, magnetically labels the exchangeable solute protons or the exchangeable solute-based water molecules; (b) allowing a portion of the magnetically labeled exchangeable solute protons to exchange with the bulk water protons or allowing the magnetically labeled exchangeable solute-based water molecules to exchange with bulk water molecules; (c) repeating (a) and (b) a plurality of times to enhance a population size of the magnetically labeled exchangeable solute protons or the magnetically labeled exchangeable solute-based water molecules; (d) irradiating the subject under observation with a water excitation RF pulse that is adapted to excite the bulk water protons; (e) recording a magnetic resonance (MR) signal from the subject under observation in response to the water excitation RF pulse; and (f) analyzing the recorded MR signal to estimate a quantity associated with the exchangeable solute protons or the exchangeable solute-based water molecules.