Early FID signal detection technique with a gradient coil for magnetic resonance sounding

Magnetic resonance sounding (MRS) is a noninvasive geophysical method that allows direct qualitative and quantitative detection of groundwater and it has been used widely to detect shallow groundwater. However, current MRS device structures suffer from tens of milliseconds of dead time due to the effect of coupling between the receiving and transmitting coils, which can lead to early data loss and signal distortion. This is especially true for small multiturn coil structures. To solve this problem, we propose an early free induction decay (FID) signal detection technique with a gradient coil for MRS, which consists of two equidistant receiving coils above and below the transmitting coil. This symmetric distribution eliminates the effect of coil coupling. Based on the proposed technique, a numerical model and a prototype of the principle were constructed. Simulation and experimental results show that the new method effectively suppresses the influence of transceiver coil coupling. The new method based on a gradient coil structure can acquire short relaxation FID signals and the dead time was reduced to 1 ms. The new method provides technical support for efficient and accurate detection of shallow groundwater.