Т₁ mapping of rat lungs in ¹⁹F MRI using octafluorocyclobutane

Abstract

Purpose To demonstrate the feasibility of using octafluorocyclobutane (OFCB, c‐C4F8) for T1 mapping of lungs in 19F MRI. Methods The study was performed at 7 T in three healthy rats and three rats with pulmonary hypertension. To increase the sensitivity of 19F MRI, a bent‐shaped RF coil with periodic metal strips structure was used. The double flip angle method was used to calculate normalized transmitting RF field (B1n+) maps and for correcting T1 maps built with the variable flip angle (VFA) method. The ultrashort TE pulse sequence was applied for acquiring MR images throughout the study. Results The dependencies of OFCB relaxation times on its partial pressure in mixtures with oxygen, air, helium, and argon were obtained. T1 of OFCB linearly depended on its partial pressure with the slope of about 0.35 ms/kPa in the case of free diffusion. RF field inhomogeneity leads to distortion of T1 maps built with the VFA method, and therefore to high standard deviation of T1 in these maps. To improve the accuracy of the T1 maps, the B1n+ maps were applied for VFA correction. This contributed to a 2–3‐fold decrease in the SD of T1 values in the corresponding maps compared with T1 maps calculated without the correction. Three‐dimensional T1 maps were obtained, and the mean T1 in healthy rat lungs was 35 ± 10 ms, and in rat lungs with pulmonary hypertension – 41 ± 9 ms. Conclusion OFCB has a spin‐rotational relaxation mechanism and can be used for 19F T1 mapping of lungs. The calculated OFCB maps captured ventilation defects induced by edema.