Perfluorocarbon temperature measurements using 19F NMR.

Measuring the T1 of the fluorine resonances of perfluorocarbons (PFC) is a unique method for monitoring oxygen tension in vivo. However, because T1 is also temperature sensitive, error in the pO2 determination due to animal-to-animal temperature variation may arise. Pathophysiologic conditions, such as ischemia, where temperature is not known a priori may also introduce error. Thus, measuring the PFC temperature is clearly desirable in order to correct for tissue temperature variations during the pO2 determination. Because the fluorine chemical shift of various fluorinated compounds has a significant temperature dependence, we evaluated the effect of temperature on the chemical shift of the fluorine resonances of perfluorotributylamine (FTBA). A linear relationship was found between chemical shift and temperature in vitro. In addition, the relative FTBA chemical shifts were essentially independent of pO2. Chemical shift temperature measurements in vivo, obtained from a 10 microL FTBA bubble in the preretinal vitreous space of the rabbit eye, were in good agreement (+/- 0.5 degrees C) with thermocouple measurements from the same location. Good agreement between the NMR determined temperature and core body temperature was also found. The implication of such temperature measurements for the ultimate accuracy of the pO2 determination based on PFC T1 measurements is discussed. To the best of our knowledge, this report describes the first absolute temperature measurement in vivo by NMR.