Some Applications of ESR to in Vivo Animal Studies and EPR Imaging
Paramagnetic centers, such as naturally occurring free radicals and paramagnetic metal ions, are of crucial importance in many biological functions. Some examples are flavoenzymes, vitamin B12, aging, oxygen radicals, and melanins. While work in the early days of ESR was limited by the size and electronic constraints of the X-band cavity, as well as the need, frequently, to freeze-clamp the sample or excised tissue, an “ideal” in vivo ESR spectrometer is one in which a live animal can be directly accommodated (Swartz et al., 1972). These latter experiments were virtually impossible with commercial X-band (9.5 GHz) instruments as the large electric field losses through water and ions would result in “cooking the animal” besides the extreme difficulty in matching the sample. Conventional X-band EPR spectrometers present several technical limitations to measurements on live animals, principally microwave heating. Hence, the first attempts at EPR imaging were limited to very small nonliving samples.
KeywordsElectron Spin Resonance Melanoma Tumor Thiyl Radical Semilog Plot Stable Nitroxide
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