Free-breathing T2∗ mapping using respiratory motion corrected averaging

Abstract

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.