Electron magnetic resonance imaging: A technical perspective

We report a review of continuous-wave and pulsed electron magnetic resonance imaging (eMRI). The hardware and methodology of each modality is presented. We also present single point imaging (SPI), spectral-spatial imaging, and Rapid-Scan (RS) eMR. eMRI is fundamentally similar to magnetic resonance imaging (MRI). An advantage of eMR is the higher gyromagnetic ratio of electrons compared to protons, allowing for lower power systems at higher frequencies. Thus, systems can have higher sensitivity without the requirement of superconducting magnets. Previous reports have shown the efficacy of eMRI in medical applications such as tissue oxygenation, tumor oxygenation, ischemia, and quantitative imaging. These applications are monitored using intravenous or intramuscular injection of electron rich free radicals which attach to oxygen within the body. The free radicals react to the partial pressure of oxygen and therefore the imaging of those radicals reveals characteristics of the surrounding tissues.