Noninvasive Temperature Measurements Using Electron Paramagnetic Resonance Spectroscopy

120 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993.A system has been developed that may be used for non-invasive in vivo temperature measurements in living systems. We use the nitroxide, 3-doxyl-5$\alpha$-cholestane, mixed in 1 mol% cholesterol and 99 mol% methyl docosanoate and encapsulated in proteinaceous microspheres (average diameter $<$2 $\mu$m). We have shown a dramatic and measurable change in the EPR spectral lineshape between 38 and 48$\sp\circ$C. This technique has many potential clinical applications, especially in optimizing the treatment of cancer with hyperthermia. Using the mid-field to high-field peakheight ratio of the EPR spectra as the temperature dependent parameter, the temperature resolution for this system is 0.2$\sp\circ$C. Encapsulation of the mixture in the microspheres provides two critical functions. First, the microspheres are easily injectable since they are smaller than the diameter of capillaries and are suspended in water. Second, the microspheres separate the mixture from the surrounding environment, thereby protecting the nitroxide from bioreduction and ensuring that the shape of the EPR spectrum is greatly affected by temperature in the range of the medium's liquid-solid transition. There was a hysteresis effect seen in the spectral lineshape for this system as the temperature was raised and then lowered between 37 and 48$\sp\circ$C. However, if the temperature of the system is kept above or below a certain critical temperature and within a small temperature range ($<$3$\sp\circ$C), the hysteresis can be avoided and accurate temperature measurements can be made. In order to increase the temperature resolution, computer simulation of the EPR spectra for the temperature measurement system was attempted. The no motion limit and fast motion limit spectra for the system were successfully simulated. Initial attempts to simulate the spectra for the system between 38 and 48$\sp\circ$C were unsuccessful.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD