PURPOSE: The purpose of this study was to develop an X-Band electron paramagnetic resonance imaging protocol for visualization of oxidative stress in biopsies.

METHODS: The developed electron paramagnetic resonance imaging protocol was based on spin trapping with the cyclic hydroxylamine spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine and X-Band EPR imaging. Computer software was developed for deconvolution and back-projection of the EPR image. A phantom containing radicals of known spatial characteristic was used for evaluation of the developed protocol. As a demonstration of the technique electron paramagnetic resonance imaging of oxidative stress was performed in six sections of atherosclerotic plaques. Histopathological analyses were performed on adjoining sections.

RESULTS: The developed computer software for deconvolution and back-projection of the EPR images could accurately reproduce the shape of a phantom of known spatial distribution of radicals. The developed protocol could successfully be used to image oxidative stress in six sections of the three ex vivo atherosclerotic plaques.

CONCLUSIONS: We have shown that oxidative stress can be imaged using a combination of spin trapping with the cyclic hydroxylamine spin probe cyclic hydroxylamine spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine and X-Band EPR imaging. A thorough and systematic evaluation on different types of biopsies must be performed in the future to validate the proposed technique. Magn Reson Med, 2014.

A one-dimensional electron paramagnetic resonance (EPR) imaging method for visualisation of dose distributions in photon fields has been developed. Pressed pellets of potassium dithionate were homogeneously irradiated in a Co-60 radiation field to 600 Gy. The EPR analysis was performed with an X-Band (9.6 GHz) Bruker E540 EPR and EPR imaging spectrometer equipped with an E540 GC2X two-axis X-band gradient coil set with gradients along the y axis (along the sample tube) and z axis (along B-0) and an ER 4108TMHS resonator. Image reconstruction, including deconvolution, baseline corrections and corrections for the resonator sensitivity, was performed using an in-house-developed Matlab code for the purpose to have a transparent and complete algorithm for image reconstruction. With this method, it is possible to visualise a dose distribution with an accuracy of similar to 5 % within +/- 5 mm from the centre of the resonator.

Electron paramagnetic resonance imaging (EPRI) was performed to visualise 2D dose distributions of homogenously irradiated potassium dithionate tablets and to demonstrate determination of 1D dose profiles along the height of the tablets. Mathematical correction was applied for each relative dose profile in order to take into account the inhomogeneous response of the resonator using X-band EPRI. The dose profiles are presented with the spatial resolution of 0.6 mm from the acquired 2D images; this value is limited by pixel size, and 1D dose profiles from 1D imaging with spatial resolution of 0.3 mm limited by the intrinsic line-width of potassium dithionate. In this paper, dose profiles from 2D reconstructed electron paramagnetic resonance (EPR) images using the Xepr software package by Bruker are focussed. The conclusion is that using potassium dithionate, the resolution 0.3 mm is sufficient for mapping steep dose gradients if the dosemeters are covering only +/- 2 mm around the centre of the resonator.