Effect of supplemental oxygen on native blood and myocardial MOLLI T1 relaxation times

Abstract

Background Magnetic resonance (MR) T1 relaxation time measurements are increasingly used for myocardial tissue characterization. Significant differences in native and gadolinium-enhanced measurements have been associated with ischemic and non-ischemic cardiomyopathies, myocardial fat deposition, fibrosis and edema as well as regional and global ventricular functional parameters. Supplemental oxygen is often given to cardiac MR patients for improved breatholding. High flow supplemental oxygen with a non-rebreather mask is reported to reduce both myocardial and blood T1 relaxation times and has been studied with HASTE and FLASH T1 relaxation measurements for the optimization of MR ventilation scanning. The primary mechanism is dissolved oxygen acting as a paramagetic contrast agent. Conversely other reports show an increase of blood T1 times with increasing oxygen saturation. We studied the effect of supplemental oxygen on myocardial and blood T1 relaxation times using a well-documented T1 MOdified Look-Locker Imaging (MOLLI) protocol. Methods Twelve healthy subject without respiratory or cardiac disease (age: 47.4±5.3 years; 6 male) were studied at 1.5T using MOLLI T1 mapping (TE/TE= 2.8/1.2 ms; 3(3)-5; 2 inversions, 3 heartbeat rest period; TI start=120 ms; TI increment=120ms; 3 parameter curve fitting). Images were acquired in the four chamber view. Five measurements spaced by 10 minutes were performed with supplemental oxygen supplied by nasal cannula and a non-reberather mask alternating with room air (M1: Room air, M2: nasal oxygen (2 l/m), M3: Room air, M4: non-rebreather mask (15 l/m), M5: room air). Regions-of-interest were drawn for T1 measurements in the boodpool of each ventricle and atria as well as septal myocardium. The effects of supplemental oxygen were investigated statistically using a mixed model analysis of variance.