Department of Bioengineering, University of California, Los Angeles, United States; Biomedical Imaging Research Institute, Cedars Sinai Medical Center, Los Angeles, United States.
J Magn Reson. 2013 Oct;235:77-84. doi: 10.1016/j.jmr.2013.08.001. Epub 2013 Aug 12.
Existing para-hydrogen induced polarization (PHIP) instrumentation relies on magnetic fields to hyperpolarize substances. These hyperpolarized substances have enhanced magnetic resonance imaging (MRI) signals over 10,000 fold, allowing for MRI at the molecular level. Required magnetic fields are generated by energizing a solenoid coil with current produced by a voltage controlled voltage source (VCVS), also known as a power supply. A VCVS lacks the current regulation necessary to keep magnetic field fluctuations to a minimum, which results in low PHIP polarization. A voltage controlled current source (VCCS) is an electric circuit that generates a steady flow of electrons proportional to an input voltage. A low noise VCCS provides the solenoid current flow regulation necessary to generate a stable static magnetic field (Bo). We discuss the design and implementation of a low noise, high stability, VCCS for magnetic field generation with minimum variations. We show that a precision, low noise, voltage reference driving a metal oxide semiconductor field effect transistor (MOSFET) based current sink, results in the current flow control necessary for generating a low noise and high stability Bo. In addition, this work: (1) compares current stability for ideal VCVS and VCCS models using transfer functions (TF), (2) develops our VCCS design's TF, (3) measures our VCCS design's thermal & 1/f noise, and (4) measures and compares hydroxyethyl-propionate (HEP) polarization obtained using a VCVS and our VCCS. The hyperpolarization of HEP was done using a PHIP instrument developed in our lab. Using our VCCS design, HEP polarization magnitude data show a statistically significant increase in polarization over using a VCVS. Circuit schematic, bill of materials, board layout, TF derivation, and Matlab simulations code are included as supplemental files.
现有的顺磁氢核极化（PHIP）仪器依赖于磁场来使物质超极化。这些超极化物质的磁共振成像（MRI）信号增强了 10000 多倍，从而可以在分子水平上进行 MRI。所需的磁场是通过用电压控制电压源（VCVS）产生的电流激励螺线管线圈产生的，VCVS 也称为电源。VCVS 缺乏将磁场波动降至最低所需的电流调节，这导致 PHIP 极化率低。电压控制电流源（VCCS）是一种产生与输入电压成正比的稳定电子流的电路。低噪声 VCCS 提供了螺线管电流流动调节的必要性，以产生稳定的静态磁场（Bo）。我们讨论了低噪声、高稳定性、VCCS 的设计和实现，以最小的变化产生磁场。我们表明，精密、低噪声的电压基准驱动基于金属氧化物半导体场效应晶体管（MOSFET）的电流源，可实现产生低噪声和高稳定性 Bo 所需的电流控制。此外，这项工作：（1）使用传递函数（TF）比较理想 VCVS 和 VCCS 模型的电流稳定性，（2）开发我们的 VCCS 设计的 TF，（3）测量我们的 VCCS 设计的热和 1/f 噪声，（4）测量并比较使用 VCVS 和我们的 VCCS 获得的羟乙基丙酸酯（HEP）极化。HEP 的超极化是在我们实验室开发的 PHIP 仪器上完成的。使用我们的 VCCS 设计，HEP 极化幅度数据显示极化强度有统计学意义的增加，超过了使用 VCVS 的情况。包括电路图、物料清单、电路板布局、TF 推导和 Matlab 仿真代码作为补充文件。
