Abstract

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are important technologies for studying small animals in vivo. They are based on the physical phenomenon of nuclear magnetic resonance (NMR), which was discovered in 1938 by I. Rabi. Nuclei with nonzero magnetic moment determined by the nuclear spin once placed in a static magnetic field B ₀ have resonant absorbance of electromagnetic energy at the resonance frequency ?₀ = ?B ₀, where ? is the gyro-magnetic ratio of the nucleus. For protons, the most abundant magnetic nuclei in biological systems, the gyromagnetic ratio is ? = 42.6 MHz/T. At typical magnetic field strengths of B ₀ = 4.7–11.7 T, which are used in small animal MR imaging and spectroscopy, the resonance radio frequency (RF) or magnetic resonance frequency is in the range of ?₀ = 200–500 MHz. Other magnetic nuclei frequently used for in vivo MR applications include ³¹P, ²³Na, ¹⁹F, and ¹³C. Compared to protons, these nuclei have lower gyromagnetic ratios and are present at significantly lower concentrations that limit detection and often require sophisticated methods to improve the efficiency of detection.