Oxygen enhanced lung MRI by simultaneous measurement of T1 and T2 * during free breathing using ultrashort TE

Abstract

Purpose: To provide a robust method for the simultaneous quantification of T1 and T2 * in the human lung during free breathing. Breathing pure oxygen accelerates T1 and T2 * relaxation in the lung. While T1 shortening reflects an increased amount of dissolved molecular oxygen in lung tissue, T2 * shortening shows an increased concentration of oxygen in the alveolar gas. Therefore, both parameters reflect different aspects of the oxygen uptake and provide complementary lung functional information.

Materials and methods: A segmented inversion recovery Look-Locker multiecho sequence based on a multiecho 2D ultrashort TE (UTE) was employed for simultaneous T1 and T2 * quantification. The radial projections follow a modified golden angle ordering, allowing for respiratory self-gating and thus the reconstruction of a series of differently T1 and T2 *-weighted images in arbitrary breathing states. The method was evaluated in nine healthy volunteers while breathing room air and pure oxygen, with two volunteers examined at five oxygen concentrations.

Results: Relative differences of ΔT1 between 7.9% and 12.7% and of ΔT2 * between 13.2% and 6.0% were found.

Conclusion: The proposed method provides inherently coregistered, quantitative T1 and T2 * maps in both expiration and inspiration from a single measurement acquired during free breathing and is thus well suited for clinical application.

Keywords: T1 mapping; T2* mapping; lung imaging; oxygen enhanced imaging.