Nuclear Magnetic Resonance Imaging

NUCLEAR magnetic resonance (NMR) imaging is a technique by which the quantitative analysis of a biological structure or tissue sample may be determined. The various approaches to be discussed in this article all depend on the fact that certain atomic nuclei behave as small magnets. When these nuclei are placed in static magnetic fields, some will align themselves in the direction of the field. In this configuration they will rotate about the field direction (precess) at a frequency that is dependent on the strength of the applied magnetic field (Bo). If in this circumstance these aligned and precessing nuclei are exposed to an alternating magnetic field (radio frequency [RF]) of the same frequency, some of these nuclei will be forced from their equilibrium state to a higher energy level. When the interrogating RF is removed, the excited nuclei will emit the added energy and return to their former state. The