F-19 CHEMICAL-SHIFT IMAGING TECHNIQUE TO MEASURE INTRACELLULAR PO(2) IN-VIVO USING PERFLUBRON

Rationale and Objectives. There is a linear relation between the T1 re laxation rate of fluorine-19 (F-19) of perfluorochemicals (PFCs) and t he partial pressure of the oxygen (pO(2)) dissolved in the PFC. A line scan technique was used to overcome the significant chemical shift an d low signal-to-noise ratio (SNR) of in vivo F-19 magnetic resonance i maging. This study was designed to determine whether the line scan tec hnique could detect the effect of oxygen on F-19 T1. In addition, its ability to detect changes in intracellular pO(2) when the inspired gas was raised from 20% to 100% O-2 also was investigated. Methods. The T 1 relaxation rate of samples of perflubron emulsion diluted from 3.5% to 70% w/v and equilibrated with N-2-O-2 gas mixtures (pO(2) range = 1 0-450 mm Hg) was measured using the line scan technique. The gas and e mulsion pO(2) were measured with a blood gas analyzer. The liver T1 re laxation rate was measured in three rabbits given 5 ml/kg perflubron e mulsion 4 and 8 days earlier as they breathed room air and then 100% O -2 We used a prototype cylindrical coil double-tuned to hydrogen-1 (H- 1) and F-19 and selected a line through the liver. The scanning parame ters yielded a voxel size of 20 x 20 x 15.6 mm. Liver and blood sample s were obtained postsacrifice for perflubron concentration measurement . Results. A linear relation between the F-19 T1 relaxation rate (1/T1 ) of the 3.5% w/v emulsion and dissolved pO(2) 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 2 1.2%. 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% O-2 (p = .023), which corresponded to an increase in intracellular pO(2) of 19.7 mm Hg. The liver-to-blood PFC concentration ratio was 500:1. C onclusion. In vitro measurements with the line scan technique replicat ed the established linear dependence of 1/T1 on pO(2). In vivo measure ments indicated a 20-mm Hg increase in intracellular pO(2) of liver ph agocytes when the inspired gas was changed from 20% to 100% O-2.