Free-breathing T2∗ mapping using respiratory motion corrected averaging

Background: pixel-wise t2∗ maps based on breath-held segmented image acquisition are prone to ghost artifacts in instances of poor breath-holding or cardiac arrhythmia. single shot imaging is inherently immune to ghost type artifacts. we propose a free-breathing method based on respiratory motion corrected single shot imaging with averaging to improve the signal to noise ratio. methods: images were acquired using a multi-echo gradient recalled echo sequence and t2∗ maps were calculated at each pixel by exponential fitting. for 40 subjects (2 cohorts),two acquisition protocols were compared: (1) a breath-held,segmented acquisition,and (2) a free-breathing,single-shot multiple repetition respiratory motion corrected average. t2∗ measurements in the interventricular septum and liver were compared for the 2-methods in all studies with diagnostic image quality. results: in cohort 1 (n = 28) with age 51.4 ± 17.6 (m ± sd) including 1 subject with severe myocardial iron overload,there were 8 non-diagnostic breath-held studies due to poor image quality resulting from ghost artifacts caused by respiratory motion or arrhythmias. in cohort 2 (n = 12) with age 30.9 ± 7.5 (m ± sd),including 7 subjects with severe myocardial iron overload and 4 subjects with mild iron overload,a single subject was unable to breath-hold. free-breathing motion corrected t2∗ maps were of diagnostic quality in all 40 subjects. t2∗ measurements were in excellent agreement (in cohort #1,t2∗fb = 0.95 x t2∗bh + 0.41,r2 = 0.93,n = 39 measurements,and in cohort #2,t2∗fb = 0.98 x t2∗bh + 0.05,r2 > 0.99,n = 22 measurements). conclusions: a free-breathing approach to t2∗ mapping is demonstrated to produce consistently good quality maps in the presence of respiratory motion and arrhythmias. © 2015 kellman et al.