Imagent BP (90% w/v perflubron emulsion) is radiopaque and serves as an X-ray contrast medium. Quantitative X-ray Computed Tomography, provides the means to non-invasively estimate tissue perflubron concentration providing three unique capabilities: 1) The use of the same animal for biodistribution and elimination analysis; 2) The precise geographic distribution of the agent to more accurately quantitate localized accumulations; and 3) The ability to gather physiologic data by monitoring the time dependent distribution of perflubron. It is known that the T1(-1) of 19F of perfluorochemicals is linearly related to the dissolved oxygen which allows the quantitation of PO2 in-vivo. We showed using perflubron in phanta that not only was T1(-1) linearly related to PO2 but also T2(-1) and both were insensitive to perflubron concentration. Since flow interferes with signal, the first in-vivo experiments have focused on stationary perflubron located within phagocytes. T1(-1) measured from this environment suggested a PO2 of 15-25 Torr. T1(-1) increased by nearly 50% when the FIO2 was increased from 20 to 100% reflecting an increase in intracellular PO2 on the order of 25 Torr.