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19F chemical shift imaging technique to measure intracellular pO2 in vivo using perflubron
H T Tran1, Q Guo, D J Schumacher
1Department of Radiology, University of California, San Diego Medical Center, USA.
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-O2 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 x 20 x 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.