| 摘要 |
A composite spin lock prepulse method compensates for magnetic field inhomogeneities in objects or materials under study using nuclear magnetic resonance (NMR). The effective magnetic field seen by an object or material under study using NMR often is characterized by an off-resonance component, which results in the magnetization of the object or material having a component that diverges from the intended orientation after RF pulses. The method according to the present invention recognizes and utilizes the observation that aligning the off-resonance component of the magnetization in the x-z plane can be achieved when the amplitude of a preceding 90 DEG y flip pulse is known, and that the effective field can be placed in alignment with the resulting magnetization, if necessary or desired, by adjusting the amplitude of the locking pulse as a function of the amplitude of the flip pulse. The method has been found to be particularly useful for enhancing contrast in images obtained using magnetic resonance imaging (MRI), and it may be conveniently applied in this and a wide variety of other NMR applications because pulse sequences of the present invention can be conveniently be inserted into existing NMR pulse sequences. In addition, the method may be used to create prepulse sequences having reduced net effective field amplitude and, thus, reduced SAR (heat absorption). |
