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Search Completed | Title | National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
Original File Name Searched: JMagnReson165_116_2003.pdf | Google It | Yahoo | Bing
Text | National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA | 001
Journal of Magnetic Resonance 165 (2003) 116–127
High resolution electron spin resonance microscopy Aharon Blank, Curt R. Dunnam, Peter P. Borbat, and Jack H. Freed*
National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
Received 22 May 2003; revised 8 July 2003
NMR microscopy is routinely employed in fields of science such as biology, botany, and materials science to observe magnetic parameters and transport phenomena in small scale structures. Despite extensive efforts, the resolution of this method is limited (>10 lm for short acquisition times), and thus cannot answer many key questions in these fields. We show, through theoretical prediction and initial experiments, that ESR microscopy, although much less developed, can improve upon the resolution limits of NMR, and successfully undertake the 1 lm resolution challenge. Our theoretical predictions demonstrate that existing ESR tech- nology, along with advanced imaging probe design (resonator and gradient coils), using solutions of narrow linewidth radicals (the trityl family), should yield 64 64 pixels 2D images (with z slice selection) with a resolution of 1 1 10 lm at 60 GHz in less than 1 h of acquisition. Our initial imaging results, conducted by CW ESR at X-band, support these theoretical predictions and already improve upon the previously reported state-of-the-art for 2D ESR image resolution achieving 10 10 lm, in just several minutes of acquisition time. We analyze how future progress, which includes improved resonators, increased frequency of measurement, and advanced pulsed techniques, should achieve the goal of micron resolution.
Ó 2003 Elsevier Inc. All rights reserved.
Keywords: ESR imaging; ESR microscope; Trityl radical; Gradient coils; High permittivity resonator
NMR microscopy is a well-established field of sci- ence, which employs the techniques of MRI with large gradients in high magnetic fields to enable high image resolution . The state-of-the-art of todayÕs NMR mi- croscope achieves voxel resolution of [3.5lm]3 in a liquid, at a frequency of 400 MHz after 30 h of data acquisition . NMR microscopy in the solid state achieves voxel resolution of [150lm]3 [3,4] and also requires several hours of data acquisition. Commercial NMR microscopes are available from several vendors and are used for characterization of tissues with fine structures, non-invasive tracing of plant metabolism, investigation of transport phenomena, histological-like applications and more [5,6]. While the field of NMR microscopy is well developed, ESR microscopy is a largely unexplored area. Most of the efforts with respect
* Corresponding author. Fax: 1-607-255-6969. E-mail address: email@example.com (J.H. Freed).
1090-7807/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S1090-7807(03)00254-4
to ESR imaging are directed towards imaging of large biological objects [7–10] and determining the radical and oxygen concentration (by its effect on the radical line- width). Such experiments, conducted in-vivo, employ low fields of 10 mT at low RF frequencies, where the RF energy penetrates well into the biological object. Consequently, a typical voxel resolution in low fre- quency ESR experiments is ca. [2 mm]3 . Most of the low field imaging techniques are based on CW detection while applying static gradients in various directions with respect to the object (the so-called back-projection technique). However, some techniques use a single pulse FID sequence in conjunction with pulsed and static gradients .
In contrast to the recent advances in low frequency ESR imaging, high frequency ESR imaging, directed to microscopy, is not well developed. The reasons may be a combination of technical difficulties and the lack of scientific interest. In our opinion, the main problem is that above a certain ‘‘threshold’’ of reasonable imaging time (several minutes to an hour) and without having a
Image | National Biomedical Center for Advanced ESR Technology, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
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