title: Intercentre reproducibility of cardiac apparent diffusion coefficient and fractional anisotropy in healthy volunteers.
abstract: BACKGROUND
  Diffusion tensor cardiac magnetic resonance (DT-CMR) enables probing of the microarchitecture of the myocardium, but the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) reported in healthy volunteers have been inconsistent. The aim of this study was to validate a stimulated-echo diffusion sequence using phantoms, and to assess the intercentre reproducibility of in-vivo diffusion measures using the sequence.
  
  
  RESULTS
  A stimulated-echo, cardiac-gated DT-CMR sequence with a reduced-field-of-view, single-shot EPI readout was used at two centres with 3 T MRI scanners. Four alkane phantoms with known diffusivities were scanned at a single centre using a stimulated echo sequence and a spin-echo Stejskal-Tanner diffusion sequence. The median (maximum, minimum) difference between the DT-CMR sequence and Stejskal-Tanner sequence was 0.01 (0.04, 0.0006) × 10(-3) mm2/s (2%), and between the DT-CMR sequence and literature diffusivities was 0.02 (0.05, 0.006) × 10(-3) mm2/s (4%).The same ten healthy volunteers were scanned using the DT-CMR sequence at the two centres less than seven days apart. Average ADC and FA were calculated in a single mid-ventricular, short axis slice. Intercentre differences were tested for statistical significance at the p < 0.05 level using paired t-tests. The mean ADC ± standard deviation for all subjects averaged over both centres was 1.10 ± 0.06 × 10(-3) mm2/s in systole and 1.20 ± 0.09 × 10-3 mm2/s in diastole; FA was 0.41 ± 0.04 in systole and 0.54 ± 0.03 in diastole. With similarly-drawn regions-of-interest, systolic ADC (difference 0.05 × 10(-3) mm2/s), systolic FA (difference 0.003) and diastolic FA (difference 0.01) were not statistically significantly different between centres (p > 0.05), and only the diastolic ADC showed a statistically significant, but numerically small, difference of 0.07 × 10(-3) mm2/s (p = 0.047). The intercentre, intrasubject coefficients of variance were: systolic ADC 7%, FA 6%; diastolic ADC 7%, FA 3%.
  
  
  CONCLUSIONS
  This is the first study to demonstrate the accuracy of a stimulated-echo DT-CMR sequence in phantoms, and demonstrates the feasibility of obtaining reproducible ADC and FA in healthy volunteers at separate centres with well-matched sequences and processing.
authors.affiliation: Oxford Centre for Clinical Magnetic Resonance Research, Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, Oxford, UK. elizabeth.tunnicliffe@cardiov.ox.ac.uk.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Tunnicliffe
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Scott
authors.forename: Pedro
authors.initials: P
authors.lastname: Ferreira
authors.forename: Rina
authors.initials: R
authors.lastname: Ariga
authors.forename: Laura-Ann
authors.initials: LA
authors.lastname: McGill
authors.forename: Sonia
authors.initials: S
authors.lastname: Nielles-Vallespin
authors.forename: Stefan
authors.initials: S
authors.lastname: Neubauer
authors.forename: Dudley J
authors.initials: DJ
authors.lastname: Pennell
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Robson
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
mesh_terms: D000328:Adult; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation; D004739:England; D005240:Feasibility Studies; D005260:Female; D064368:Healthy Volunteers; D006321:Heart / Q000033:anatomy & histology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D055815:Young Adult