¹⁹F‐MRI of perflubron for measurement of oxygen partial pressure in porcine lungs during partial liquid ventilation

Abstract

Perfluorocarbon compounds (PFCs) have received increasing interest for medical applications because of the high solubility of gases like O 2 and CO 2 in these substances (1). In addition, the suitability of PFCs as a respiratory medium is favored by their low surface tension and biological inertness. With the intrapulmonary application of PFCs, a new therapeutic strategy for the treatment of acute respiratory distress syndrome (ARDS) was developed. This technique is called partial liquid ventilation (PLV) and was first described by Fuhrman et al. in 1991 (2).During PLV, gas exchange is achieved by delivering gas tidal volumes into a lung which has previously been filled with a PFC. In the last few years, several clinical studies have been published focusing on the use of PLV in premature infants as well as in adult ARDS (3,4). However, until now the mechanisms by which PLV improves gas exchange and pulmonary function were not completely understood. Numerous studies have examined the influence of PLV on pulmonary gas exchange and systemic blood gas parameters. Although knowledge of the regional distribution of intrapulmonary oxygen partial pressure (pO2) during PLV is crucial for the understanding of PLV, this distribution has not been measured before.Recently, several methods for quantitative determination of pO2 based on 19 F-MRI of perfluorocarbon compounds have been suggested (1,5-9). Paramagnetic oxygen reduces the longitudinal relaxation time (T 1 ) of the 19 F MR resonances in PFCs. This effect can be used for the generation of an oxygen-dependent MR signal intensity in T 1 -weighted images. Nö th et al. (8) presented a technique based on a chemical shift selective (CHESS) TurboFLASH sequence allowing for the determination of regional pO2. In their study, that sequence was applied in vivo to investigate the regional distribution of pO2 in rats after intravenous injection of a perfluorocarbon emulsion.The first objective of this study was to develop a technique for a visualization of the intrapulmonary distribution of PFC during PLV with high spatial resolution. The second objective was to develop a methodology for the quantification of regional pO2 during PLV of pigs. Special consideration was given to suppress systematic errors by noise and results of a pilot study using this new technique in a healthy pig during PLV are presented. MATERIALS AND METHODS Measurements Experimental SetupAll data were acquired on a 1.5 T Siemens Magnetom Vision whole body scanner with a prototype gradient system (50 mT/m, slew rate 160 mT m -1 ms -1 ). A birdcage RF coil (RAPID Biomedical GmbH, Wü rzburg, Germany) was used for RF transmission and reception. The fluorinated contrast agent used in the animal study was neat liquid perfluoro-octyl-bromide (PFOB) C 8 F 17 Br (LiquiVent , Alliance Pharm. Corp., San Diego, CA, USA).With animal committee approval, in vivo measurements were performed in a healthy, anesthetized pig (body weight, 18 kg) under conditions of PLV. The lungs were filled in part with 20 mL PFOB/kg body weigh...

MRI of lungs using partial liquid ventilation with water‐in‐perfluorocarbon emulsions

“…2e and f is higher than that of the 19 F-MR lung image of PFCs as shown in Fig. 4, and that similar results have been reported previously (12)(13)(14). This is because the concentration of 19 F in PFCs is much lower than that of 1 H in the PFC emulsions, and there is no 19 tissue.…”

“…4. It should be mentioned that in a recent publication Laukemper-Ostendorf et al (13) stated that during PLV with PFOB emulsions, the 19 F MRI of PFOB in the lung resulted in images with low SNR.…”

“…Because of its low sensitivity, it still suffers from the limitation of long examination times and residual signal from fat or muscle. Many attempts have been made to develop 19 F MRI of lungs (12)(13)(14) and other organs (15-18) using a variety of perfluorocarbon (PFC) emulsions. However, this methodology still suffers from low sensitivity and low spatial resolution due to low concentrations and the presence of multiple fluorine peaks in the 19 F spectra of many fluorocarbons.…”

Dynamic 19F‐MRI of pulmonary ventilation using sulfur hexafluoride (SF6) gas

“…However, the wash-in of these aerosols critically depends on the size of the aerosol particles (i.e., on the production of the aerosol), which limits quantitative applications of this method as well. Further approaches comprise fluorine-19 ( 19 F) MRI either of 19 F-containing fluids (9,10) or of inert fluorinated gases in the lung (11,12). Whereas the first of these two 19 F MRI approaches has been demonstrated in animals and, most probably, will have a limited role in humans, the second one is of particular interest for human applications.…”

Rapid monitoring of oxygenation by 19F magnetic resonance imaging: Simultaneous comparison with fluorescence quenching

“…Finally, the mouse was sacrificed using 5% isoflurane in air for 20 min. Parametric images of the spin-lattice relaxation time (T 1 ) were estimated using a snapshot inversion recovery (SNAP-IR) pulse sequence (13)(14)(15). The pulse sequence consisted of a nonselective hyperbolic secant inversion pulse (10 ms length), followed by acquisition of a series of 512 rapid gradient echo images (repetition time ϭ 10.9 ms, echo time ϭ 4.2 ms, flip angle ϭ 1°, matrix ϭ 32 ϫ 16, field of view ϭ 60 ϫ 30 mm, bandwidth ϭ 12.5 kHz, single thick slice [projection], total acquisition time ϭ 1.5 min) (Fig.…”