title: Free-breathing myocardial T2* mapping using GRE-EPI and automatic non-rigid motion correction.
abstract: BACKGROUND
  Measurement of myocardial T2* is becoming widely used in the assessment of patients at risk for cardiac iron overload. The conventional breath-hold, ECG-triggered, segmented, multi-echo gradient echo (MGRE) sequence used for myocardial T2* quantification is very sensitive to respiratory motion and may not be feasible in patients who are unable to breath-hold. We propose a free-breathing myocardial T2* mapping approach that combines a single-shot gradient-echo echo-planar imaging (GRE-EPI) sequence for T2*-weighted image acquisition with automatic non-rigid motion correction (MOCO) of respiratory motion between single-shot images.
  
  
  METHODS
  ECG-triggered T2*-weighted images at different echo times were acquired by a black-blood, single-shot GRE-EPI sequence during free-breathing. A single image at a single TE is acquired in each heartbeat. Automatic non-rigid MOCO was applied to correct for in-plane respiratory motion before pixel-wise T2* mapping. In a total of 117 patients referred for clinical cardiac magnetic resonance exams, the free-breathing MOCO GRE-EPI sequence was compared to the breath-hold segmented MGRE approach. Image quality was scored independently by 2 experienced observers blinded to the particular image acquisition strategy. T2* measurements in the interventricular septum and in the liver were compared for the two methods in all cases with adequate image quality.
  
  
  RESULTS
  T2* maps were acquired in all 117 patients using the breath-hold MGRE and the free-breathing MOCO GRE-EPI approaches, including 8 patients with myocardial iron overload and 25 patients with hepatic iron overload. The mean image quality of the free-breathing MOCO GRE-EPI images was scored significantly higher than that of the breath-hold MGRE images by both reviewers. Out of the 117 studies, 21 breath-hold MGRE studies (17.9% of all the patients) were scored to be less than adequate or very poor by both reviewers, while only 2 free-breathing MOCO GRE-EPI studies were scored to be less than adequate image quality. In a comparative evaluation of the images with at least adequate quality, the intra-class correlation coefficients for myocardial and liver T2* were 0.868 and 0.986 respectively (p < 0.001), indicating that the T2* measured by breath-hold MGRE and free-breathing MOCO GRE-EPI were in close agreement. The coefficient of variation between the breath-hold and free-breathing approaches for myocardial and liver T2* were 9.88% and 9.38% respectively. Bland-Altman plots demonstrated good absolute agreement of T2* in the interventricular septum and the liver from the free-breathing and breath-hold approaches (mean differences -0.03 and 0.16 ms, respectively).
  
  
  CONCLUSIONS
  The free-breathing approach described for T2* mapping using MOCO GRE-EPI enables accurate myocardial and liver T2* measurements and is insensitive to respiratory motion.
authors.affiliation: Siemens Medical Solutions USA, Inc, 460 West 12th Ave, Room 311, OH 43210, Columbus, OH, USA. ning.jin@siemens.com.
authors.forename: Ning
authors.initials: N
authors.lastname: Jin
authors.affiliation: Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA. juliana.serafimdasilveira@osumc.edu.
authors.forename: Juliana Serafim
authors.initials: JS
authors.lastname: da Silveira
authors.affiliation: Imaging & Computer Vision, Siemens Corporation, Corporate Technology, Princeton, NJ, USA. marie-pierre.jolly@siemens.com.
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Jolly
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK. d.firmin@imperial.ac.uk.|National Heart and Lung Institute, Imperial College, London, UK. d.firmin@imperial.ac.uk.
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK. g.mathew@rbht.nhs.uk.
authors.forename: George
authors.initials: G
authors.lastname: Mathew
authors.affiliation: Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA. nathan.lamba@osumc.edu.
authors.forename: Nathan
authors.initials: N
authors.lastname: Lamba
authors.affiliation: Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA. sharath.subramanian@osumc.edu.
authors.forename: Sharath
authors.initials: S
authors.lastname: Subramanian
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Trust, London, UK. d.pennell@imperial.ac.uk.|National Heart and Lung Institute, Imperial College, London, UK. d.pennell@imperial.ac.uk.
authors.forename: Dudley J
authors.initials: DJ
authors.lastname: Pennell
authors.affiliation: Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA. subha.raman@osumc.edu.|Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA. subha.raman@osumc.edu.
authors.forename: Subha V
authors.initials: SV
authors.lastname: Raman
authors.affiliation: Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH, USA. orlando.simonetti@osumc.edu.|Department of Internal Medicine - Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA. orlando.simonetti@osumc.edu.|Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA. orlando.simonetti@osumc.edu.|Department of Radiology, The Ohio State University, Columbus, OH, USA. orlando.simonetti@osumc.edu.
authors.forename: Orlando P
authors.initials: OP
authors.lastname: Simonetti
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001331:Automation; D015415:Biomarkers / Q000378:metabolism; D055424:Cardiac-Gated Imaging Techniques; D009202:Cardiomyopathies / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D002648:Child; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007501:Iron / Q000378:metabolism*; D019190:Iron Overload / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D008131:London; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D015588:Observer Variation; D009820:Ohio; D011237:Predictive Value of Tests; D011379:Prognosis; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012720:Severity of Illness Index; D055815:Young Adult
chemical_list: D015415:Biomarkers; D007501:Iron