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Electron paramagnetic resonance imaging (EPRI) is one of the recent functional imaging modalities that can provide
valuable in vivo physiological information on its own merit and aids as a complimentary imaging technique to MRI and
PET of tissues especially with respect to in vivo pO2 (oxygen partial pressure), redox status and pharmacology. EPR
imaging mainly deals with the measurement of distribution and in vivo dynamics and redox changes using special nontoxic
paramagnetic spin probes that can be infused into the object of investigation. These spin probes should be
characterized by simple EPR spectra, preferably with narrow EPR lines. The line width should be reversibly sensitive
to the concentration of in vivo pO2 with a linear dependence. Several non-toxic paramagnetic probes, some particulate
and insoluble and others water-soluble and infusible (by intravenous or intramuscular injection) have been developed
which can be effectively used to quantitatively assess tissue redox status, and tumor hypoxia. Quantitative assessment
of the redox status of tissue in vivo is important in investigating oxidative stress, and that of tissue pO2 is very important
in radiation oncology. Other areas in which EPR imaging and oxymetry may help are in the investigation of tumorangiogenesis,
wound healing, oxygenation of tumor tissue by the ingestion of oxygen-rich gases, etc. The correct choice
of the spin probe will depend on the modality of measurement (whether by CW or time-domain EPR imaging) and the
particular physiology interrogated. Examples of the available spin probes and some EPR imaging applications
employing them are presented.
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