Т mapping of rat lungs in F MRI using octafluorocyclobutane.

PURPOSE

To demonstrate the feasibility of using octafluorocyclobutane (OFCB, c-C F ) for T mapping of lungs in F 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 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 ) maps and for correcting T 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 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 maps built with the VFA method, and therefore to high standard deviation of T in these maps. To improve the accuracy of the T maps, the B maps were applied for VFA correction. This contributed to a 2-3-fold decrease in the SD of T values in the corresponding maps compared with T maps calculated without the correction. Three-dimensional T maps were obtained, and the mean T 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 F T mapping of lungs. The calculated OFCB maps captured ventilation defects induced by edema.