Comparison of 2-D ESR imaging techniques in two frequency ranges

Abstract

Two-dimensional pulsed electron spin resonance (ESR) imaging was developed in two frequency ranges (radio frequency at 370 MHz and X-band at 9.5 GHz) using the Fourier imaging (FI) and filtered back projection (FBP) technique. A comparison and evaluation of FI and FBP images in both frequency ranges shows the superiority of the FBP method under the given conditions. Benefits and drawbacks of the different frequency ranges are analyzed with respect to the signal-to-noise ratio and the disturbing influences of the skin effect. Examples for the mapping of dynamic properties (e.g., relaxation times, diffusion coefficient) are given. Functional imaging is illustrated using variable temperature for discriminating radiation-induced differences in physical sample properties.

Conduction-Electron Drift Velocity Measurement via Electron Spin Resonance

“…Rotating a magnetic field gradient across selected planes through the sample, we could obtain two-dimensional electronic density-weighted images using the so-called back-projection reconstruction method [14,[21][22][23]. Figure 2 shows one such ESR image of the very same contacted FA 2 PF 6 crystal used for the current experiments (length 1.9 mm, cross section A 0:8 mm 2 ).…”

Three-dimensional cylindrical X-band ESR imaging by a combined pulsed gradient Fourier and static gradient projection reconstruction method

“…This arrangement is capable of quasi static currents (200 ls) of 1.6 A and pulsed gradients of 1 T/m and about 1.5 ls length without breakdown. As usual, the gradient pulses were produced with a pulse driver based on the ''clipped L-C resonant circuit'' idea [16,8,9]. Maximum phase encoding values of…”

“…Thus the pulse separation time s = 500 ns commonly used for this buildup has to be increased to s = 3 ls and therewith a loss of about 50% signal intensity has to be taken. A home-build software package for 2d image reconstruction written in C was adapted for the algorithm of cylindrical imaging introduced in Section 2.1 [9,12]. To correct for a possible out of rotation axis mounting of the sample, the centers of gravity of the one-dimensionally projected signals S(q,/) and S(q,/ + p) were centered numerically.…”

“…Hence, spin echo detection in rotated static magnetic field gradients and the filtered back projection technique was easier to handle in two-dimensional pulsed ESR imaging [9]. Unfortunately, the ''simple'' extension to the three-dimensional version of filtered back projection imaging with static magnetic field gradient [10] is prohibited in quasione-dimensional conductors, because the conduction electron spin motion in the preferred direction (with 10 4 :1 anisotropy of the diffusion coefficient) tends to give rise to imaging artefacts [11].…”

A versatile high speed 250‐MHz pulse imager for biomedical applications

“…100×100×100) requires almost a half million measurements, each in the presence of a different gradient (see the Materials and Methods section). Analogous to the MRI spin echo experiment (25, 26), a number of laboratories have developed electron spin echo imaging (ESE) at high frequencies (27–30). Mailer et al demonstrated accurate oxygen images using three dimensional time-domain ESE imaging at 250 MHz (31).…”