扫场对核磁共振测量的影响

摘要

在连续波核磁共振实验中，通常采用低频扫场产生重复再现的共振吸收信号。当处于磁场中的射频线圈引线回路等效面积不为零时，简谐扫场必然引起该闭合回路的磁通量变化，由此而产生同频简谐感生电动势并与核磁共振信号叠加共同构成振荡器输出信号。由于扫场上升和下降过程的感生电动势方向相反，从而扫场前半周和后半周所对应的共振吸收测量信号存在差异。实验结果表明：扫场强度及方向对核磁共振测量影响来源于实验测量技术缺陷，而非核磁共振的物理本质。%The resonance absorption was generated using a magnet with the low‐frequency modu‐lation field in the continuous wave nuclear magnetic resonance experiment .When the loop area vertical to magnet was not zero , the flux in the closed loop caused by the modulation magnetic field was changed ,then the induced electromotive force would be added to the nuclear magnetic resonance sig‐nal .Because the rising and falling of the modulation field induced opposite electromotive forces ,the resonance absorption signals for the first and second half period of the modulation field were different . The experiment showed that the reason for the influence from magnitude and orientation of modula‐tion field was not attributed to its physics but the defect of measurement technique .