Continuous Wave Electron Paramagnetic Resonance Imaging

项目3：连续波电子顺磁共振成像。进展摘要：我们对现有的300 MHz CW机器进行了改进，增加了一个可以在高交流频率下工作的磁场扫描线圈。我们测试了现有的用于高频操作的梯度线圈，发现它们只能在1 kHz的频率下使用。通过采用0.33 kHz的场扫描和1 kHz的旋转梯度(通过在两个正交的梯度线圈中应用正弦梯度，我们可以获得对应于2G/cm幅度的左或右旋转梯度电流)，这是2D成像所需的。利用美国国家仪器公司的LabVIEW软件和美国国家仪器公司的PCI-6289多功能数据采集卡产生了较低频率的快速扫描信号、三个较高的频率梯度信号和数据采集的触发信号。调节梯度信号的幅度以产生在XZ平面上以所选频率旋转的圆极化梯度场。然后，X和Z梯度的相位可以以所需的步长间隔相对于快速扫描场以编程方式递增。来自射频电桥的EPR信号被下变频到基带，使用低噪声低频放大器放大，并使用商用数字转换器兼夏季Acqiris AP100(Acqiris USA，Monroe，CA)双通道信号捕获。通过在第三正交线圈中进一步施加正弦电流，可以以相等的倾斜角倾斜旋转梯度平面，以覆盖以3D空间编码所需的谐振器为中心的梯度轨迹的整个半球。由于投影是通过扫描场和同时的梯度旋转来收集的，所以必须通过简单的矩阵混洗程序来重新组织观测信号，以得到传统的笛卡尔投影，然后使用这些笛卡尔投影通过滤波反投影来生成图像。即使在这种适度的扫描频率下，每次投影也可以在不到15毫秒的时间内完成。我们可以用这种所谓的快速扫描旋转梯度模式收集2D和3D投影数据，速度至少比传统的CW方法快50-100倍。这项发明受到了一项美国申请的保护。

Project 3: Continuous Wave Electron Paramagnetic Resonance Imaging. Summary of Progress: We have modified our existing 300 MHz CW machine by supplementing a field sweep coil that can work at high AC frequencies. We tested the existing gradient coils for high frequency operation, and found that they can be used only up to a frequency of 1 kHz. By employing field sweeps at 0.33 kHz, and rotating gradients at 1 kHz (by applying sinusoidal gradients in two orthogonal gradient coils we could accomplish a left- or right-rotating gradient current corresponding to 2G/cm amplitude) required for 2D imaging. The lower frequency rapid scan signal, the three higher frequency gradient signals, and the trigger signals for data acquisition were generated using National Instruments LabView software and National Instrument PCI-6289 multifunction data acquisition card. The amplitudes of the gradient signals are adjusted to result in a circularly polarized gradient field rotating in the XZ plane at the selected frequency. The phase of the X and Z gradients can then be incremented programmatically relative to the rapid scan field at a desired step interval. The EPR signals from the RF bridge are down-converted to base band and amplified using a low noise low frequency amplifier and captured using a commercial digitizer-cum-summer Acqiris AP100 (Acqiris USA, Monroe, CA) dual channel Signal. By further applying a sinusoidal current in the third orthogonal coil, one can tilt the rotating gradient plane in equal tilt angles to cover an entire hemisphere of gradient trajectories centered on the resonator that is required for 3D spatial encoding. Since the projections are collected with the sweep field and simultaneous gradient rotation, one has to reorganize the observed signals by a simple matrix shuffling program to give the conventional Cartesian projections which are then used to generate the image by filtered back-projection. Even with this modest sweep frequency each projection could be carried out in less than 15 ms. We could collect 2D and 3D projection data in this so-called Rapid-scan-rotating gradient modality at least 50-100 times faster than the conventional CW approach. The invention has been protected by a US application.