Use of Imagent BP (PFOB) in diagnostic imaging and F-19 magnetic resonance for PO2 measurements

Perfluorooctylbromide (PFOB) is an effective contrast medium to image the blood pool, liver, and spleen by computed tomography (CT) (PFOB is radiopaque) and sonography. PFOB also allows the detection of tumors immediately post infusion and on delayed scans (1-2 days) with both modalities. At 1-2 days, it is found in the perivascular space of tumors totally contained within macrophages. The use of CT with PFOB allows the non-invasive determination of the fractional blood volume of tissues as well as the geographic distribution of PFOB within tumors. It is known that F-19 MR 1/Tl of PFOB is linearly related to the dissolved oxygen, which allows the quantitation of tissue p 02 in vivo. It is therefore possible to measure tissue vascular p02 as well as the p02 within the intracellular environment, if acquisition is done when PFOB is within phagocytes. The purpose of this presentation is to demonstrate the capabilities of CT and MR in PFOB research to determine biodistribution, tissue fractional blood volume, geographic distribution within lesions, and the measurement of p02 changes within tissues and within cells. The F-19 signal was acquired, using a one-dimensional spectroscopic spin-echo sequence from a receiver only coil-tuned to the F-19 resonance at 1.5 T. T1-relaxation was measured by partial saturation recovery. We have shown that this method is insensitive to F-19 concentration and linear to ambient p02. Our study showed that when PFOB was given to rabbits 5-7 days before imaging (negligible blood level at imaging time) it allowed the detection of a significant p02 change in the liver, the spleen, and thigh abscess, which is known to accumulate PFOB within macrophages, when the FIO2 changed from 20% to 100%. The detected change must reflect alteration in intracellular p02 caused by the increased FIO2.