¹⁹F chemical shift imaging technique to measure intracellular pO₂ in vivo using perflubron

Rationale and Objectives.: There is a linear relation between the T1 relaxation rate of fluorine-19 (¹⁹F) of perfluorochemicals (PFCs) and the partial pressure of the oxygen (pO₂) dissolved in the PFC. A line scan technique was used to overcome the significant chemical shift and low signal-to-noise ratio (SNR) of in vivo ¹⁹F magnetic resonance imaging. This study was designed to determine whether the line scan technique could detect the effect of oxygen on ¹⁹F T1. In addition, its ability to detect changes in intracellular pO₂ when the inspired gas was raised from 20% to 100% O₂ also was investigated. Methods.: The T1 relaxation rate of samples of perflubron emulsion diluted from 3.5% to 70% w/v and equilibrated with N₂-0₂ gas mixtures (pO₂ range = 10-450 mm Hg) was measured using the line scan technique. The gas and emulsion pO₂ were measured with a blood gas analyzer. The liver T1 relaxation rate was measured in three rabbits given 5 ml/kg perflubron emulsion 4 and 8 days earlier as they breathed room air and then 100% O₂. We used a prototype cylindrical coil double-tuned to hydrogen-1 (¹H) and ¹⁹F and selected a line through the liver. The scanning parameters yielded a voxel size of 20 × 20 × 15.6 mm. Liver and blood samples were obtained postsacrifice for perflubron concentration measurement. Results.: A linear relation between the ¹⁹F T1 relaxation rate (1/T1) of the 3.5% w/v emulsion and dissolved pO₂ was established with a slope of 0.0033 (sec^-1/mm Hg) and a correlation coefficient of .991. As the PFC concentration increased by 1,900%, the slope increased by 21.2%. The 1/T1 for the liver was 0.182 ± 0.004 sec^-1 at baseline. It increased to 0.247 ± 0.022 sec^-1 when rabbits breathed 100% O₂ (p = .023), which corresponded to an increase in intracellular pO₂ of 19.7 mm Hg. The liver-to-blood PFC concentration ratio was 500:1. Conclusion.: In vitro measurements with the line scan technique replicated the established linear dependence of 1/T1 on pO₂. In vivo measurements indicated a 20-mm Hg increase in intracellular pO₂ of liver phagocytes when the inspired gas was changed from 20% to 100% O₂.