Direct detection and time-locked subsampling applied to pulsed electron paramagnetic resonance imaging.

Area of Science:

• Electron Paramagnetic Resonance Spectroscopy
• Radio Frequency Spectroscopy
• Digital Signal Processing

Background:

• Conventional Fourier Transform Electron Paramagnetic Resonance (FT-EPR) spectroscopy often requires intermediate frequency (IF) stages to down-convert high Larmor frequencies (L(f)).
• This is particularly relevant for in vivo studies which utilize FT-EPR systems with lower L(f), such as 300 MHz.
• Advancements in bandpass sampling and signal processing technologies offer new possibilities for simplifying FT-EPR systems.

Purpose of the Study:

• To describe the application of direct time-locked subsampling (TLSS) to a 300 MHz FT-EPR system operating at radio frequencies (rf).
• To demonstrate the feasibility of omitting the IF stage in FT-EPR systems by utilizing TLSS.
• To outline the necessary modifications for data acquisition and processing, and custom software development for this application.

Main Methods:

• Direct time-locked subsampling (TLSS) was applied to directly sample the 300 MHz free induction decay (FID) signal at an 80 MHz sampling rate, yielding a 20 MHz signal bandwidth.
• Modifications were made to the data acquisition and processing systems to accommodate direct sampling.
• Custom software was developed for system control, signal acquisition, and data post-processing.
• Data was acquired using both coherent averaging and stochastic excitation sequences.

Main Results:

• The experiments successfully demonstrated the digital down-conversion of the 300 MHz FID signal to quadrature baseband.
• Direct FID TLSS eliminated noise sources associated with traditional analog receiver techniques, including IF mixer stages.
• The method proved effective in simplifying the FT-EPR receiver architecture.

Conclusions:

• Direct time-locked subsampling (TLSS) is a viable technique for simplifying FT-EPR spectroscopy at radio frequencies.
• This method enables direct digital acquisition of the FID signal, reducing noise and hardware complexity.
• TLSS offers a promising approach for in vivo FT-EPR studies by eliminating the need for intermediate frequency stages.