Evaluation of a high-speed signal-averager for sensitivity enhancement in radio frequency Fourier transform electron paramagnetic resonance imaging

Abstract

A commercially available high-speed, digital signal-averager is integrated into an existing time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager. Sensitivity enhancement by the integrated system is estimated by coherent averaging of free induction decay signals, obtained from narrow-line EPR spin probes, and its performance is compared with that of an existing custom-built averager. For the existing custom-built “Analytek” averager, the minimum realizable trigger rate was 50 kHz, whereas for the commercial EG&G 9826 system, due the spectrometer constraints, we set the retrigger rate to 133 kHz. Very short summing and down loading times of the latter enable good temporal resolution in phantom as well as in vivo rf Fourier transform EPR images, obtained by the single point imaging (SPI) modality. For two-dimensional and three-dimensional imaging using the SPI mode, a saving of time by a factor of >2 could be achieved with the EG&G system compared with the Analytek.