title: Stochastic excitation and Hadamard correlation spectroscopy with bandwidth extension in RF FT-EPR.
abstract: The application of correlation spectroscopy employing stochastic excitation and the Hadamard transform to time-domain Fourier transform electron paramagnetic resonance (FT-EPR) spectroscopy in the radiofrequency (RF) band is described. An existing, time-domain FT-EPR spectrometer system with a Larmor frequency (L(f)) of 300 MHz was used to develop this technique by incorporating a pseudo-random pulse sequence generator to output the maximum length binary sequence (MLBS, 10- and 11-bit). Software developed to control the EPR system setup, acquire the signals, and post process the data, is outlined. The software incorporates the Hadamard transform algorithm to perform the required cross-correlation of the acquired signal and the MLBS after stochastic excitation. To accommodate the EPR signals, bandwidth extension was accomplished by sampling at a rate many times faster than the RF pulse repetition rate, and subsequent digital signal processing of the data. The results of these experiments showed that there was a decrease in the total acquisition time, and an improved free induction decay (FID) signal-to-noise (S/N) ratio compared to the conventional coherent averaging approach. These techniques have the potential to reduce the RF pulse power to the levels used in continuous wave (CW) EPR while retaining the advantage of time-domain EPR methods. These methods have the potential to facilitate the progression to in vivo FT-EPR imaging of larger volumes.
authors.affiliation: Signal Processing and Instrumentation Section, Division of Computational Biosciences, Center for Information Technology, National Institutes of Health, 12 South Dr, Bldg 12A-2025, Bethesda, MD 20892-1002, USA. pursley@nih.gov
authors.forename: Randall H
authors.initials: RH
authors.lastname: Pursley
authors.forename: John
authors.initials: J
authors.lastname: Kakareka
authors.forename: Ghadi
authors.initials: G
authors.lastname: Salem
authors.forename: Nallathamby
authors.initials: N
authors.lastname: Devasahayam
authors.forename: Sankaran
authors.initials: S
authors.lastname: Subramanian
authors.forename: Rolf G
authors.initials: RG
authors.lastname: Tschudin
authors.forename: Murali C
authors.initials: MC
authors.lastname: Krishna
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Pohida
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000295:instrumentation*; D004867:Equipment Design; D005583:Fourier Analysis; D011846:Radio Waves; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012984:Software; D013269:Stochastic Processes