A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications
A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications
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DOI：
10.1063/1.1148857
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发表时间：
1998-04-01
影响因子：
1.6
通讯作者：
Krishna, MC
中科院分区：
文献类型：
--
作者：
Murugesan, R;Afeworki, M;Krishna, MC
本文描述了一种能探测和成像生物体内自由基的时域射频（rf）电子顺磁共振（EPR）谱仪/成像仪（EPRI）。使用高速门产生来自信号发生器的20-70 ns的短脉冲，上升时间小于4 ns，在放大到283 Vpp之后，将其沉积到包含感兴趣对象的谐振器中。圆柱形谐振器包含在均匀间距的平行环用于成像实验。通过调谐和匹配电容器将谐振器保持在谐振频率。并联电阻和过耦合电路用于实现20-30范围内的Q值。发射和接收臂使用发射/接收双工器隔离。脉冲后沿后的死区时间约为450 ns。接收臂的第一级包含低噪声、高增益和快速恢复放大器，适用于检测自旋-自旋弛豫时间（T-2）为μ s量级的自旋探针。感应信号的检测是通过将以300 MHz为中心的接收器臂中的信号与频率为350 MHz的本地振荡器混合来进行的。使用1 GHz数字转换器/加法器对放大的信号进行数字化和求和，以恢复信号并提高信噪比（SNR）。利用傅里叶变换（FT）将时域信号转换为频域谱。使用共振器，可以在成像实验中研究尺寸高达5 cm（3）的物体。在1.0-1.5 G/cm范围内的静态场梯度存在下，通过样品的体积激发来完成自旋的空间编码。自旋密度以平面积分的形式产生，并使用标准反投影方法重建图像。使用梯度时，包含自旋探针的体模物体的图像分辨率优于0.2 mm，该体模物体被有耗生物介质包围。为了在局部位置检查较大的物体，表面线圈被用来成功地检测和成像自旋探针。这项研究的结果表明，在体内应用的rf FT EPR的潜力。特别是，rf FT EPR可以提供一种手段来获得生理信息，如组织氧合和氧化还原状态。(C)1998年美国物理学会。
A time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager (EPRI) capable of detecting and imaging free radicals in biological objects is described, The magnetic field was 10 mT which corresponds to a resonance frequency of 300 MHz for paramagnetic species. Short pulses of 20-70 ns from the signal generator, with rise times of less than 4 ns, were generated using high speed gates, which after amplification to 283 Vpp, were deposited into a resonator containing the object of interest. Cylindrical resonators containing parallel loops at uniform spacing were used for imaging experiments. The resonators were maintained at the resonant frequency by tuning and matching capacitors. A parallel resistor and overcoupled circuit was used to achieve Q values in the range 20-30. The transmit and receive arms were isolated using a transmit/receive diplexer. The dead time following the trailing edge of the pulse was about 450 ns. The first stage of the receive arm contained a low noise, high gain and fast recovery amplifier, suitable for detection of spin probes with spin-spin relaxation times (T-2) in the order of mu s. Detection of the induction signal was carried out by mixing the signals in the receiver arm centered around 300 MHz with a local oscillator at a frequency of 350 MHz. The amplified signals were digitized and summed using a 1 GHz digitizer/summer to recover the signals and enhance the signal-to-noise ratio (SNR). The time-domain signals were transformed into frequency-domain spectra, using Fourier transformation (FT). With the resonators used, objects of size up to 5 cm(3) could be studied in imaging experiments. Spatial encoding of the spins was accomplished by volume excitation of the sample in the presence of static field gradients in the range of 1.0-1.5 G/cm. The spin densities were produced in the form of plane integrals and images were reconstructed using standard back-projection methods. The image resolution of the phantom objects containing the spin probe surrounded by lossy biologic medium was better than 0.2 mm with the gradients used. To examine larger objects at local sites, surface coils were used to detect and image spin probes successfully. The results from this study indicate the potential of rf FT EPR for in vivo applications. In particular, rf FT EPR may provide a means to obtain physiologic information such as tissue oxygenation and redox status. (C) 1998 American Institute of Physics.