Pursley Randall H, Salem Ghadi, Devasahayam Nallathamby, Subramanian Sankaran, Koscielniak Janusz, Krishna Murali C, Pohida Thomas J
Signal Processing and Instrumentation Section, Division of Computational Biosciences, Center for Information Technology, National Institutes of Health, 12 South Drive, Bldg. 12A-2025, Bethesda, MD 20892-1002, USA.
J Magn Reson. 2006 Feb;178(2):220-7. doi: 10.1016/j.jmr.2005.10.001. Epub 2005 Oct 21.
The integration of modern data acquisition and digital signal processing (DSP) technologies with Fourier transform electron paramagnetic resonance (FT-EPR) imaging at radiofrequencies (RF) is described. The FT-EPR system operates at a Larmor frequency (L(f)) of 300MHz to facilitate in vivo studies. This relatively low frequency L(f), in conjunction with our approximately 10MHz signal bandwidth, enables the use of direct free induction decay time-locked subsampling (TLSS). This particular technique provides advantages by eliminating the traditional analog intermediate frequency downconversion stage along with the corresponding noise sources. TLSS also results in manageable sample rates that facilitate the design of DSP-based data acquisition and image processing platforms. More specifically, we utilize a high-speed field programmable gate array (FPGA) and a DSP processor to perform advanced real-time signal and image processing. The migration to a DSP-based configuration offers the benefits of improved EPR system performance, as well as increased adaptability to various EPR system configurations (i.e., software configurable systems instead of hardware reconfigurations). The required modifications to the FT-EPR system design are described, with focus on the addition of DSP technologies including the application-specific hardware, software, and firmware developed for the FPGA and DSP processor. The first results of using real-time DSP technologies in conjunction with direct detection bandpass sampling to implement EPR imaging at RF frequencies are presented.
描述了现代数据采集和数字信号处理（DSP）技术与射频（RF）傅里叶变换电子顺磁共振（FT-EPR）成像的集成。FT-EPR系统在300MHz的拉莫尔频率（L(f)）下运行，以利于体内研究。这个相对较低的频率L(f)，结合我们大约10MHz的信号带宽，使得能够使用直接自由感应衰减时间锁定子采样（TLSS）。这种特殊技术通过消除传统的模拟中频下变频阶段以及相应的噪声源而具有优势。TLSS还产生了易于管理的采样率，便于基于DSP的数据采集和图像处理平台的设计。更具体地说，我们利用高速现场可编程门阵列（FPGA）和DSP处理器来执行先进的实时信号和图像处理。向基于DSP的配置的迁移带来了EPR系统性能提高的好处，以及对各种EPR系统配置（即软件可配置系统而非硬件重新配置）的适应性增加。描述了对FT-EPR系统设计所需的修改，重点是添加DSP技术，包括为FPGA和DSP处理器开发的专用硬件、软件和固件。展示了将实时DSP技术与直接检测带通采样相结合以在RF频率下实现EPR成像的初步结果。
