| 摘要 |
The effects of a spurious free induction decay (FID) NMR signal due to imperfect 180 DEG RF pulses are eliminated by phase alternating the selective 90 DEG RF pulses and subtracting alternate ones of the NMR signals. The desired signals due to the 90 DEG RF pulses reinforce, while the signals produced by the imperfect 180 DEG pulses cancel. This method also has the beneficial effect of eliminating DC offset in the desired signal which, when present, causes artifacts in NMR images. Another method to eliminate the effects of spurious FID signals due to imperfect 180 DEG pulses is to phase alternate these 180 DEG pulses on successive NMR imaging pulse sequences and add successive NMR signals. In this case, the phase shifted spurious FID signals cancel, while the desired NMR signals reinforce. The latter method does not eliminate the effects of DC offset, however. |
