T-1 mapping of rat lungs in F-19 MRI using octafluorocyclobutane

Purpose: To demonstrate the feasibility of using octafluorocyclobutane (OFCB, c-C4F8) for T-1 mapping of lungs in F-19 MRI.Methods: The study was performed at 7 T in three healthy rats and three rats with pulmonary hypertension. To increase the sensitivity of F-19 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 (B-1n(+)) maps and for correcting T-1 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. T-1 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 T-1 maps built with the VFA method, and therefore to high standard deviation of T-1 in these maps. To improve the accuracy of the T-1 maps, the B-1n(+) maps were applied for VFA correction. This contributed to a 2-3-fold decrease in the SD of T-1 values in the corresponding maps compared with T-1 maps calculated without the correction. Three-dimensional T-1 maps were obtained, and the mean T-1 in healthy rat lungs was 35 & PLUSMN; 10 ms, and in rat lungs with pulmonary hypertension - 41 & PLUSMN; 9 ms.Conclusion: OFCB has a spin-rotational relaxation mechanism and can be used for F-19 T-1 mapping of lungs. The calculated OFCB maps captured ventilation defects induced by edema.