Quantitative mapping of ventilation‐perfusion ratios in lungs by 19 F MR imaging of T 1 of inert fluorinated gases

A new method is presented for quantitative mapping of ventilation‐to‐perfusion ratios (V A /Q) in the lung: MRI of the 19 F longitudinal relaxation time ( T 1 ) of an inert fluorinated gas at thermal polarization. The method takes advantage of the dependence of the 19 F T 1 on the local SF 6 partial pressure, which depends on the local value of V A /Q. In contrast to hyperpolarized noble gases, with very long T 1 s, the T 1 of SF 6 in mammal lungs is 0.8–1.3 ms. Thus, rapid signal averaging overcomes the low thermal equilibrium polarization. T 1 imaging of a phantom consisting of four different SF 6 /air mixtures with known T 1 values validates the modified Look‐Locker T 1 imaging sequence. To demonstrate the method in vivo, partial obstruction of the left bronchus was attempted in three rats; 3D free induction decay (FID)‐projection T 1 images (2 mm isotropic resolution) revealed obstructed ventilation in two of the animals. In those images, ≈1700 lung voxels contained sufficient SF 6 for analysis and T 1 was determined in each voxel with a standard error of 8–10%. For comparison, independent V A /Q images of the same animals were obtained using a previously described SF 6 MRI technique, and good agreement between the two techniques was obtained. Relative to the previous technique the resolution achieved using the T 1 method is lower (for similar V A /Q precision and imaging time); however, the T 1 method offers the potential advantages of eliminating the need for image coregistration and allowing patients with impaired lung function to breathe a 70% O 2 gas mixture during the entire imaging procedure. Magn Reson Med 59:739–746, 2008. © 2008 Wiley‐Liss, Inc.