title: Heterogeneity of Fractional Anisotropy and Mean Diffusivity Measurements by In Vivo Diffusion Tensor Imaging in Normal Human Hearts.
abstract: BACKGROUND
  Cardiac diffusion tensor imaging (cDTI) by cardiovascular magnetic resonance has the potential to assess microstructural changes through measures of fractional anisotropy (FA) and mean diffusivity (MD). However, normal variation in regional and transmural FA and MD is not well described.
  
  
  METHODS
  Twenty normal subjects were scanned using an optimised cDTI sequence at 3T in systole. FA and MD were quantified in 3 transmural layers and 4 regional myocardial walls.
  
  
  RESULTS
  FA was higher in the mesocardium (0.46 ±0.04) than the endocardium (0.40 ±0.04, p≤0.001) and epicardium (0.39 ±0.04, p≤0.001). On regional analysis, the FA in the septum was greater than the lateral wall (0.44 ±0.03 vs 0.40 ±0.05 p = 0.04). There was a transmural gradient in MD increasing towards the endocardium (epicardium 0.87 ±0.07 vs endocardium 0.91 ±0.08×10-3 mm2/s, p = 0.04). With the lateral wall (0.87 ± 0.08×10-3 mm2/s) as the reference, the MD was higher in the anterior wall (0.92 ±0.08×10-3 mm2/s, p = 0.016) and septum (0.92 ±0.07×10-3 mm2/s, p = 0.028). Transmurally the signal to noise ratio (SNR) was greatest in the mesocardium (14.5 ±2.5 vs endocardium 13.1 ±2.2, p<0.001; vs epicardium 12.0 ± 2.4, p<0.001) and regionally in the septum (16.0 ±3.4 vs lateral wall 11.5 ± 1.5, p<0.001). Transmural analysis suggested a relative reduction in the rate of change in helical angle (HA) within the mesocardium.
  
  
  CONCLUSIONS
  In vivo FA and MD measurements in normal human heart are heterogeneous, varying significantly transmurally and regionally. Contributors to this heterogeneity are many, complex and interactive, but include SNR, variations in cardiac microstructure, partial volume effects and strain. These data indicate that the potential clinical use of FA and MD would require measurement standardisation by myocardial region and layer, unless pathological changes substantially exceed the normal variation identified.
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Laura-Ann
authors.initials: LA
authors.lastname: McGill
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Scott
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Pedro F
authors.initials: PF
authors.lastname: Ferreira
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom.
authors.forename: Sonia
authors.initials: S
authors.lastname: Nielles-Vallespin
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Tevfik
authors.initials: T
authors.lastname: Ismail
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Kilner
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Gatehouse
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Ranil
authors.initials: R
authors.lastname: de Silva
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Prasad
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Archontis
authors.initials: A
authors.lastname: Giannakidis
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
authors.affiliation: NIHR Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom; National Heart and Lung Institute, Imperial College, London, United Kingdom.
authors.forename: Dudley J
authors.initials: DJ
authors.lastname: Pennell
mesh_terms: D000328:Adult; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006321:Heart / Q000033:anatomy & histology*; D006331:Heart Diseases / Q000175:diagnosis; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult