Continuous Wave Electron Paramagnetic Resonance Imaging

项目三：连续波电子顺磁共振成像。进展概述：我们已经开发出在10秒内收集三维图像的能力。有了这种能力，我们可以在体内以前所未有的时间分辨率成像顺磁性物质，如氮氧化物、一氧化氮加合物等。我们必须修改谐振器组件和平台进行体内实验。现有的连续波方法包括使用恒定的矢量场梯度和相对缓慢的磁场扫描，以及使用场调制（一种被称为相敏检测的信号检测方法）。使用相敏检测，它要求扫描速度慢（秒），使得多维成像的图像数据采集时间长得不可接受（30分钟），用于体内应用。我们在300 MHz频率下开发了一种新的连续波成像策略，该策略结合了三种方法来收集图像数据，增加了空间、时间和光谱分辨率，从而提高了单位时间测量的灵敏度。首先，采用直接检测策略，将信号混合到基带，用快速数字化仪直接采集数据，进行光谱数据采集。其次，在梯度磁场下，采用快速正弦磁场扫描获取投影；第三，梯度本身是圆极化的，并与正弦扫描同步应用。通过这种方法，图像数据收集变得非常高效。通过实施数字信号处理（DSP）技术，进一步加强了灵敏度的提高，该技术消除了光谱仪中模拟设备产生的几种噪声源。连续波光谱仪的模块化设计由优化的DSP（数字信号处理）发送和接收系统组成，该系统允许选择预编程的2D和3D以及从发送模块中选择的多个频率和所需投影的光谱空间图像数据收集，交互式DSP接收和图像重建系统允许优化信号平均程度以获得满意的图像质量等。这种快速成像策略在几乎达到时域（脉冲EPR）模式速度的连续波EPR中的适用性已经在虚幻和体内成像实验中得到了成功的测试。目前，我们使用1.5 mT振幅的1.2 kHz正弦场扫描和4.8 kHz旋转梯度，最大振幅为40mT/m。这种配置受现有梯度放大器的限制，EPR图像的测量时间如下：单64点投影：205秒；2D图像64x64 52.4 ms；3D图像63x64x64 3.35秒。这些速度接近时域模态的速度。然而，由于连续波光谱不受线宽（或脉冲模式下的横向弛缓时间）的限制，这种快速扫描旋转梯度直接检测策略将在快速测量氮氧化物、自旋捕获的一氧化氮和其他生物上重要的自由基方面非常强大，这些自由基在低频下无法通过脉冲方法轻易检测到。我们正在进一步探索通过购买更高功率的交流放大器来增加扫描和梯度旋转频率的可能性。同时，该技术在组织氧化还原状态跟踪、连续波EPR氧饱和度测定和一氧化氮捕获研究等方面的应用也在进行中。正在尝试从物体内部选择切片，将测量限制在有限的位置，并进一步提高时间分辨率。需要指出的是，该谐振器组件也适用于MRI-EPRI共同注册。项目三：连续波电子顺磁共振成像。进展概述：我们已经开发出在10秒内收集三维图像的能力。有了这种能力，我们可以在体内以前所未有的时间分辨率成像顺磁性物质，如氮氧化物、一氧化氮加合物等。我们必须修改谐振器组件和平台进行体内实验。现有的连续波方法包括使用恒定的矢量场梯度和相对缓慢的磁场扫描，以及使用场调制（一种被称为相敏检测的信号检测方法）。使用相敏检测，它要求扫描速度慢（秒），使得多维成像的图像数据采集时间长得不可接受（30分钟），用于体内应用。我们在300 MHz频率下开发了一种新的连续波成像策略，该策略结合了三种方法来收集图像数据，增加了空间、时间和光谱分辨率，从而提高了单位时间测量的灵敏度。首先，采用直接检测策略，将信号混合到基带，用快速数字化仪直接采集数据，进行光谱数据采集。其次，在梯度磁场下，采用快速正弦磁场扫描获取投影；第三，梯度本身是圆极化的，并与正弦扫描同步应用。通过这种方法，图像数据收集变得非常高效。通过实施数字信号处理（DSP）技术，进一步加强了灵敏度的提高，该技术消除了光谱仪中模拟设备产生的几种噪声源。连续波光谱仪的模块化设计由优化的DSP（数字信号处理）发送和接收系统组成，该系统允许选择预编程的2D和3D以及从发送模块中选择的多个频率和所需投影的光谱空间图像数据收集，交互式DSP接收和图像重建系统允许优化信号平均程度以获得满意的图像质量等。这种快速成像策略在几乎达到时域（脉冲EPR）模式速度的连续波EPR中的适用性已经在虚幻和体内成像实验中得到了成功的测试。目前，我们使用1.5 mT振幅的1.2 kHz正弦场扫描和4.8 kHz旋转梯度，最大振幅为40mT/m。这种配置受现有梯度放大器的限制，EPR图像的测量时间如下：单64点投影：205秒；2D图像64x64 52.4 ms；3D图像63x64x64 3.35秒。这些速度接近时域模态的速度。然而，由于连续波光谱不受线宽（或脉冲模式下的横向弛缓时间）的限制，这种快速扫描旋转梯度直接检测策略将在快速测量氮氧化物、自旋捕获的一氧化氮和其他生物上重要的自由基方面非常强大，这些自由基在低频下无法通过脉冲方法轻易检测到。我们正在进一步探索通过购买更高功率的交流放大器来增加扫描和梯度旋转频率的可能性。同时，该技术在组织氧化还原状态跟踪、连续波EPR氧饱和度测定和一氧化氮捕获研究等方面的应用也在进行中。正在尝试从对象内部选择切片，以将测量限制在有限的位置，并进一步改进[摘要截断为7800个字符]

Project 3: Continuous Wave Electron Paramagnetic Resonance Imaging. Summary of Progress: We have developed capabilities to collect images in three dimensions in under 10 seconds. With this capability, we can image paramagnetic species such as nitroxides, adducts of nitric oxide etc. in vivo with unprecedented temporal resolution. We have to modify the resonator assembly and platform for in vivo experimentation. Existing CW methodologies involve using a constant vector field gradient and relatively slow sweep of magnetic field and the use of field modulation, a signal detection method known as phase-sensitive detection. The use phase sensitive detection, which mandates scans which are slow (seconds) making the image data acquisition times for multidimensional imaging unacceptably long (> 30 minutes) for in vivo applications.. We have developed a novel CW imaging strategy at 300 MHz frequency that incorporates three approaches to collect image data with increased spatial, temporal, and spectral resolution and thereby improve the sensitivity of measurement for unit time. Firstly, the spectral data acquisition is carried out using direct-detection strategies by mixing the signals to base-band and directly acquiring the data with a fast-digitizer. Secondly, the projections are acquired using fast sinusoidal magnetic field sweep under gradient magnetic fields. Thirdly, gradients themselves are circularly polarized and applied in synchrony with the sinusoidal sweep. With such an approach the image data collection becomes extremely efficient. The sensitivity improvements is further accentuated by implementing digital signal processing (DSP) techniques, which eliminate several sources of noise originating from analog devices in the spectrometer. The modular design of the CW spectrometer consists of optimized DSP (digital signal processing) transmit and receive systems, that allows a choice of pre-programmed 2D and 3D and spectral-spatial image data collection at a number of frequencies and desired number of projections to be selected from the transmitter module, an interactive DSP receive and image reconstruction system that allows optimizing the extent of signal averaging for satisfactory image quality, etc. The applicability of such a fast imaging strategy in CW EPR that almost reaches the speed of time-domain (pulsed EPR) modality has already been tested successfully in phantom and in vivo imaging experiments. Currently we use 1.2 kHz sinusoidal field sweeps of 1.5 mT amplitude, and 4.8 kHz rotating gradients with maximum amplitude 40mT/m. With this configuration which is constrained by our existing gradient amplifiers, the measurement times for EPR images are as follows: Single 64 point projection: 205 s; 2D image 64x64 52.4 ms; 3D image 63x64x64 3.35 s. These speeds approach that of time domain modalities. However, since CW spectroscopy is not handicapped by the line width (or transverse relaxation times as in the pulsed mode) this rapid-scan rotating-gradient direct detection strategy will be very powerful in fast measurement of nitroxides, spin trapped nitric oxide, and other biologically important free radicals that cannot be easily detected by pulsed methods at low frequencies. We are further exploring the possibility of increasing the sweep and gradient rotation frequencies by procuring higher power AC amplifiers. In the meanwhile applications of this technique for following tissue redox status, CW EPR oxymetry and studies on trapping of nitric oxide, etc, are on the anvil. Attempts are being made in selecting slices from within the object to restrict the measurement to limited locations and to further improve temporal resolution. It is to be pointed that this resonator assembly is also amenable for MRI-EPRI co-registration.Project 3: Continuous Wave Electron Paramagnetic Resonance Imaging. Summary of Progress: We have developed capabilities to collect images in three dimensions in under 10 seconds. With this capability, we can image paramagnetic species such as nitroxides, adducts of nitric oxide etc. in vivo with unprecedented temporal resolution. We have to modify the resonator assembly and platform for in vivo experimentation. Existing CW methodologies involve using a constant vector field gradient and relatively slow sweep of magnetic field and the use of field modulation, a signal detection method known as phase-sensitive detection. The use phase sensitive detection, which mandates scans which are slow (seconds) making the image data acquisition times for multidimensional imaging unacceptably long (> 30 minutes) for in vivo applications.. We have developed a novel CW imaging strategy at 300 MHz frequency that incorporates three approaches to collect image data with increased spatial, temporal, and spectral resolution and thereby improve the sensitivity of measurement for unit time. Firstly, the spectral data acquisition is carried out using direct-detection strategies by mixing the signals to base-band and directly acquiring the data with a fast-digitizer. Secondly, the projections are acquired using fast sinusoidal magnetic field sweep under gradient magnetic fields. Thirdly, gradients themselves are circularly polarized and applied in synchrony with the sinusoidal sweep. With such an approach the image data collection becomes extremely efficient. The sensitivity improvements is further accentuated by implementing digital signal processing (DSP) techniques, which eliminate several sources of noise originating from analog devices in the spectrometer. The modular design of the CW spectrometer consists of optimized DSP (digital signal processing) transmit and receive systems, that allows a choice of pre-programmed 2D and 3D and spectral-spatial image data collection at a number of frequencies and desired number of projections to be selected from the transmitter module, an interactive DSP receive and image reconstruction system that allows optimizing the extent of signal averaging for satisfactory image quality, etc. The applicability of such a fast imaging strategy in CW EPR that almost reaches the speed of time-domain (pulsed EPR) modality has already been tested successfully in phantom and in vivo imaging experiments. Currently we use 1.2 kHz sinusoidal field sweeps of 1.5 mT amplitude, and 4.8 kHz rotating gradients with maximum amplitude 40mT/m. With this configuration which is constrained by our existing gradient amplifiers, the measurement times for EPR images are as follows: Single 64 point projection: 205 s; 2D image 64x64 52.4 ms; 3D image 63x64x64 3.35 s. These speeds approach that of time domain modalities. However, since CW spectroscopy is not handicapped by the line width (or transverse relaxation times as in the pulsed mode) this rapid-scan rotating-gradient direct detection strategy will be very powerful in fast measurement of nitroxides, spin trapped nitric oxide, and other biologically important free radicals that cannot be easily detected by pulsed methods at low frequencies. We are further exploring the possibility of increasing the sweep and gradient rotation frequencies by procuring higher power AC amplifiers. In the meanwhile applications of this technique for following tissue redox status, CW EPR oxymetry and studies on trapping of nitric oxide, etc, are on the anvil. Attempts are being made in selecting slices from within the object to restrict the measurement to limited locations and to further improv [summary truncated at 7800 characters]