Electron paramagnetic resonance: a powerful tool to support magnetic resonance imaging research

Abstract

The purpose of this paper is to describe some of the areas where electron paramagnetic resonance (EPR) has provided unique information to MRI developments. The field of application mainly encompasses the EPR characterization of MRI paramagnetic contrast agents (gadolinium and manganese chelates, nitroxides) and superparamagnetic agents (iron oxide particles). The combined use of MRI and EPR has also been used to qualify or disqualify sources of contrast in MRI. Illustrative examples are presented with attempts to qualify oxygen sensitive contrast (i.e. T1 - and T2 *-based methods), redox status or melanin content in tissues. Other areas are likely to benefit from the combined EPR/MRI approach, namely cell tracking studies. Finally, the combination of EPR and MRI studies on the same models provides invaluable data regarding tissue oxygenation, hemodynamics and energetics. Our description will be illustrative rather than exhaustive to give to the readers a flavour of 'what EPR can do for MRI'.

Imaging tumor acidosis: a survey of the available techniques for mapping in vivo tumor pH

“…Electron paramagnetic resonance (EPR) is a spectroscopic technique based on the detection of unpaired electrons (radicals) in paramagnetic species, exposing the sample to a sweep of microwave frequency irradiation. Because of the insufficient amount of radical species in viable tissues combined with their fast relaxation, the use of paramagnetic probes to reach a sufficient concentration at the site of interest is required [121]. Whereas direct detection of paramagnetic probes guarantees high specificity, development of probes endowed with good biocompatibility, long stability during the measurement, low toxicity, and optimal spectral sensitivity is not a straightforward task.…”

17O MRS assesses the effect of mild hypothermia on oxygen consumption rate in tumors

“…EPR oximetry was used as it provides quantitative and very sensitive measurements of tissue oxygenation. The method is also a relevant tool to calibrate other oxygen‐sensitive methods, such as MRI and positron emission tomography (PET) …”

Across the spectrum: integrating multidimensional metal analytics forin situmetallomic imaging

“…Traditionally, EPR has been used to characterize metal centres in both isolated and purified proteins and model compounds 2. However, EPR has probably gained its widest biological potential yet as EPR Imaging (EPRI) within the context of biomedical research 3. With EPRI, imaging of tissue O 2 partial pressure ( p O 2 )4 and reactive oxygen species (ROS) microenvironments is possible and ideal in the sense that it is both non-invasive and quantitative so that it can be carried out as an in vivo technique (Fig.…”