title: Dual-phase cardiac diffusion tensor imaging with strain correction.
abstract: OBJECTIVE
  In this work we present a dual-phase diffusion tensor imaging (DTI) technique that incorporates a correction scheme for the cardiac material strain, based on 3D myocardial tagging.
  
  
  METHODS
  In vivo dual-phase cardiac DTI with a stimulated echo approach and 3D tagging was performed in 10 healthy volunteers. The time course of material strain was estimated from the tagging data and used to correct for strain effects in the diffusion weighted acquisition. Mean diffusivity, fractional anisotropy, helix, transverse and sheet angles were calculated and compared between systole and diastole, with and without strain correction. Data acquired at the systolic sweet spot, where the effects of strain are eliminated, served as a reference.
  
  
  RESULTS
  The impact of strain correction on helix angle was small. However, large differences were observed in the transverse and sheet angle values, with and without strain correction. The standard deviation of systolic transverse angles was significantly reduced from 35.9±3.9° to 27.8°±3.5° (p<0.001) upon strain-correction indicating more coherent fiber tracks after correction. Myocyte aggregate structure was aligned more longitudinally in systole compared to diastole as reflected by an increased transmural range of helix angles (71.8°±3.9° systole vs. 55.6°±5.6°, p<0.001 diastole). While diastolic sheet angle histograms had dominant counts at high sheet angle values, systolic histograms showed lower sheet angle values indicating a reorientation of myocyte sheets during contraction.
  
  
  CONCLUSIONS
  An approach for dual-phase cardiac DTI with correction for material strain has been successfully implemented. This technique allows assessing dynamic changes in myofiber architecture between systole and diastole, and emphasizes the need for strain correction when sheet architecture in the heart is imaged with a stimulated echo approach.
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
authors.forename: Christian T
authors.initials: CT
authors.lastname: Stoeck
authors.affiliation: Department of Mechanical and Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Kalinowska
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Constantin
authors.initials: C
authors.lastname: von Deuster
authors.affiliation: Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Jack
authors.initials: J
authors.lastname: Harmer
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: Rachel W
authors.initials: RW
authors.lastname: Chan
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Department of Cardiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Niemann
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Department of Cardiology, University Hospital Zurich, Zurich, Switzerland; Department of Radiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Robert
authors.initials: R
authors.lastname: Manka
authors.affiliation: Centre for Medical Imaging, University College London, London, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Atkinson
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America; Cardiovascular Research Center, Cardiology Division, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: David E
authors.initials: DE
authors.lastname: Sosnovik
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America; Department of Radiology, University Hospital Center of Nîmes, EA 2415, Nîmes, France; Faculty of Medicine, Montpellier 1 University, Montpellier, France.
authors.forename: Choukri
authors.initials: C
authors.lastname: Mekkaoui
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kozerke
mesh_terms: D000328:Adult; D016880:Anisotropy; D062485:Breath Holding; D003971:Diastole / Q000502:physiology; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006321:Heart / Q000502:physiology; D006339:Heart Rate; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D009068:Movement / Q000502:physiology*; D009206:Myocardium / Q000473:pathology*; D013599:Systole / Q000502:physiology; D055815:Young Adult