Electron paramagnetic resonance (EPR) spectroscopy has been successfully employed to determine radiation dose using alanine. The EPR signal intensity reflects the number of stable free radicals produced, and provides a quantitative measurement of the absorbed dose. The aim of the present study was to explore whether this principle can be extended to provide information on spatial dose distribution using EPR imaging (EPRI). Lithium formate was selected because irradiation induces a single EPR line, a characteristic that is particularly convenient for imaging purposes. (125)I-brachytherapy seeds were inserted in tablets made of lithium formate. Images were acquired at 1.1 GHz. Monte Carlo (MC) calculations were used for comparison. The dose gradient can be determined using two-dimensional (2D) EPR images. Quantitative data correlated with the dose estimated by the MC simulations, although differences were observed. This study provides a first proof-of-concept that EPRI can be used to estimate the gradient dose distribution in phantoms after irradiation.
PurposeThe purpose of this study was to develop an X-Band electron paramagnetic resonance imaging (EPRI) protocol for visualisation of oxidative stress in biopsies.
MethodsThe developed EPRI protocol was based on spin trapping with the cyclic hydroxylamine spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH) 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 EPRI of oxidative stress was performed in six sections of atherosclerotic plaques. Histopathological analyses were performed on adjoining sections.
ResultsThe 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.
ConclusionWe have shown that oxidative stress can be imaged using a combination of spin trapping with the cyclic hydroxylamine spin probe CMH 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.
Ammonium formate is a suitable material under certain conditions for use in brachytherapy dosimetry using EPRI. In this study, the authors demonstrated that the EPRI technique allows the estimation of the relative radial dose distribution at short distances for a 192Ir wire source.
A one dimensional EPR imaging method for visualization of dose distributions in photon fields has been developed. Pressed pellets of potassium dithionate were homogenously irradiated in a 60 Co 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 y axis (along the sample tube) and z axis (along B0) and an ER 4108TMHS resonator. Image reconstruction, including deconvolution, base-line 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 visualize a dose distribution with an accuracy of about 5 % within ± 5 mm from the center of the resonator.
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