title: Ultra broadband NMR spectroscopy using multiple rotating frame technique.
abstract: The paper describes the design of broadband excitation and inversion pulses by method of multiple rotating frame technique. The ideal situation for perfect excitation and inversion is to have no chemical shift offset and thereby everything on resonance. However, when chemical shifts span a wide range, this condition is not realized. We achieve this condition using a multiply modulated rf-field, whose effect can be understood by progressing into multiple frames. As we progress through the frames, the ratio of chemical shift dispersion to strength of static rf-field decreases, resulting in a final frame, where there is negligible chemical shift as compared to the effective rf-field and we get good excitation and inversion. Increasing the number of frames, increases excitation bandwidth and the ratio of bandwidth to rms excitation amplitude. We show, in principle, it is possible to excite arbitrary large bandwidth for a given rms rf-amplitude by increasing the number of frames. The time of excitation increases linearly with the bandwidth when we keep the rms rf-amplitude constant. Experimental demonstration of proposed method is presented on (1)H excitation over a bandwidth of 52 kHz with a rms amplitude of 10 kHz. Increasing the frames increases excitation bandwidth for same rms amplitude of 10 kHz. Experimental spectra obtained from 100%(13)C labeled arginine shows uniform excitation over the entire carbon spectra, obtained with a 8-frame pulse sequence.
authors.affiliation: Department of Electrical Engineering, IIT Bombay, Powai 400076, India. Electronic address: navinkhaneja@gmail.com.
authors.forename: Navin
authors.initials: N
authors.lastname: Khaneja
authors.affiliation: NMR Research Center, IISc Banglore, India.
authors.forename: Abhinav
authors.initials: A
authors.lastname: Dubey
authors.affiliation: NMR Research Center, IISc Banglore, India.
authors.forename: Hanudatta S
authors.initials: HS
authors.lastname: Atreya
mesh_terms: D000465:Algorithms; D001120:Arginine / Q000737:chemistry; D002247:Carbon Isotopes; D003198:Computer Simulation; D004574:Electromagnetic Fields; D009682:Magnetic Resonance Spectroscopy / Q000295:instrumentation / Q000379:methods*; D011522:Protons; D015203:Reproducibility of Results
chemical_list: D002247:Carbon Isotopes; D011522:Protons; D001120:Arginine
keywords: Broadband excitation; Broadband inversion; Chemical shift; Multiple rotating frames