title: 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.
authors.affiliation: National Heart, Lung, and Blood Institute, National Institutes of Health, DHHS, 10 Center Drive MSC-1061, Bethesda 20892, MD, USA. kellman@nih.gov.
authors.forename: Peter
authors.initials: P
authors.lastname: Kellman
authors.forename: Hui
authors.initials: H
authors.lastname: Xue
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Spottiswoode
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Sandino
authors.forename: Michael S
authors.initials: MS
authors.lastname: Hansen
authors.forename: Amna
authors.initials: A
authors.lastname: Abdel-Gadir
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Treibel
authors.forename: Stefania
authors.initials: S
authors.lastname: Rosmini
authors.forename: Christine
authors.initials: C
authors.lastname: Mancini
authors.forename: W Patricia
authors.initials: WP
authors.lastname: Bandettini
authors.forename: Laura-Ann
authors.initials: LA
authors.lastname: McGill
authors.forename: Peter
authors.initials: P
authors.lastname: Gatehouse
authors.forename: James C
authors.initials: JC
authors.lastname: Moon
authors.forename: Dudley J
authors.initials: DJ
authors.lastname: Pennell
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Arai
mesh_terms: D000328:Adult; D016477:Artifacts; D062485:Breath Holding; D015331:Cohort Studies; D006346:Heart Septum / Q000473:pathology; D006801:Humans; D008099:Liver / Q000473:pathology; D019028:Magnetic Resonance Imaging, Cine; D008875:Middle Aged; D008955:Models, Cardiovascular; D009206:Myocardium / Q000473:pathology; D012119:Respiration