Quantitative mapping of ventilation-perfusion ratios in lungs by 19F MR imaging of T1 of inert fluorinated gases

✍ Scribed by Natalie L. Adolphi; Dean O. Kuethe

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 693 KB
• Volume: 59
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.21579

✦ Synopsis

Abstract

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.