用于低场MRI的基于共基极BJT的低输入阻抗LNA概念
A Concept of LNA with Low Input Impedance Using Common Base BJT for Low-Field MRI
AI总结：
该研究针对低场MRI中低输入阻抗LNA匮乏的问题，提出基于双极型晶体管共基极电路的低成本LNA，经测试其性能优于商用产品，适配低场MRI应用。
AI中文摘要：
目的：在磁共振成像（MRI）中，前置放大器去耦用于提高多通道接收线圈阵列的信噪比。在低场和超低场MRI中，具有低输入阻抗（LII）的低噪声放大器（LNA）解决方案很少，且大多采用场效应晶体管。我们提出一种基于双极型晶体管共基极电路的低成本LNA，以实现LII（<5欧姆）、低噪声系数（<1.3分贝）和高增益（>30分贝）。方法：对所提出的LNA电路进行仿真、制造，并在3兆赫和21.2兆赫频率下测试。实验评估了该LNA的去耦能力，并在0.5T MRI扫描仪中进行了MR成像，同时与商用LNA进行对比研究。在3兆赫时，通过分析自由感应衰减信号对该LNA进行评估。结果：所提出的LNA解决方案在输入阻抗为3欧姆时，噪声系数低于1.3分贝。还表明，该LNA电路在MR成像中能实现高信噪比（SNR）值。所开发的放大器在所选高频（HF）频段内，相比现有商用选项表现出更优性能。结论：由于所选晶体管的可用性和成本效益，所提出的LNA电路非常适合低场MRI应用。
英文摘要：
Purpose: In magnetic resonance imaging (MRI), preamplifier decoupling is used to improve the signal-to-noise ratio of a multichannel receive coil array. In low-field and ultra-low-field MRI, low-noise amplifier (LNA) solutions with low input impedance (LII) are poorly represented and consist mostly of field-effect transistors. We propose a low-cost LNA based on a common-base circuit with bipolar transistors to achieve LII (<5 Ohm), a low noise figure (<1.3 dB), and high gain (>30 dB). Methods: The proposed LNA circuits were simulated, fabricated, and tested at frequencies of 3 MHz and 21.2 MHz. The decoupling capabilities of the proposed LNA were experimentally evaluated, and MR imaging was performed in a 0.5T MRI scanner alongside a comparative study with a commercial LNA. At 3 MHz, the LNA was evaluated by analyzing free induction decay signals. Results: Proposed LNA solutions demonstrate a low noise figure below 1.3 dB with an input impedance of 3 Ohm. It was also shown that the presented LNA circuit enables high SNR values in MR imaging. The developed amplifiers demonstrate superior performance compared to available commercial options within the selected HF band. Conclusion: Due to the availability and cost-effectiveness of the selected transistors, the proposed LNA circuit is highly suitable for low-field MRI applications.
