Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
Magn Reson Med. 2012 Sep;68(3):989-96. doi: 10.1002/mrm.23274. Epub 2012 Jan 13.
A completely wireless detection coil with an integrated parametric amplifier has been constructed to provide local amplification and transmission of MR signals. The sample coil is one element of a parametric amplifier using a zero-bias diode that mixes the weak MR signal with a strong pump signal that is obtained from an inductively coupled external loop. The NMR sample coil develops current gain via reduction in the effective coil resistance. Higher gain can be obtained by adjusting the level of the pumping power closer to the oscillation threshold, but the gain is ultimately constrained by the bandwidth requirement of MRI experiments. A feasibility study here shows that on a NaCl/D(2) O phantom, (23) Na signals with 20 dB of gain can be readily obtained with a concomitant bandwidth of 144 kHz. This gain is high enough that the integrated coil with parametric amplifier, which is coupled inductively to external loops, can provide sensitivity approaching that of direct wire connection.
已经构建了一个完全无线的检测线圈，带有集成的参量放大器，用于提供局部放大和磁共振信号的传输。样品线圈是使用零偏置二极管的参量放大器的一个元件，它将弱磁共振信号与从感应耦合外部环路获得的强泵浦信号混合。NMR 样品线圈通过减小有效线圈电阻来获得电流增益。通过将泵浦功率的水平调整得更接近振荡阈值，可以获得更高的增益，但增益最终受到 MRI 实验带宽要求的限制。这里的一项可行性研究表明，在 NaCl/D(2)O 模型上，通过感应耦合到外部环路的参量放大器，可以获得 20dB 的增益，同时带宽为 144kHz，很容易获得 (23)Na 信号。这种增益足够高，因此与直接导线连接相比，具有参量放大器的集成线圈可以提供接近的灵敏度。
