title: Cardiovascular magnetic resonance myocardial feature tracking using a non-rigid, elastic image registration algorithm: assessment of variability in a real-life clinical setting.
abstract: BACKGROUND
  Cardiovascular magnetic resonance myocardial feature tracking (CMR-FT) is a promising technique for quantification of myocardial strain from steady-state free precession (SSFP) cine images. We sought to determine the variability of CMR-FT using a non-rigid elastic registration algorithm recently available in a commercial software package (Segment, Medviso) in a real-life clinical setting.
  
  
  METHODS
  Firstly, we studied the variability in a healthy volunteer who underwent 10 CMR studies over five consecutive days. Secondly, 10 patients were selected from our CMR database yielding normal findings (normal group). Finally, we prospectively studied 10 patients with known or suspected myocardial pathology referred for further investigation to CMR (patient group). In the patient group a second study was performed respecting an interval of 30 min between studies. All studies were manually segmented at the end-diastolic phase by three observers. In all subjects left ventricular (LV) circumferential and radial strain were calculated in the short-axis direction (EccSAXand ErrSAX,respectively) and longitudinal strain in the long-axis direction (EllLAX). The level of CMR experience of the observers was 2 weeks, 6 months and >20 years.
  
  
  RESULTS
  Mean contouring time was 7 ± 1 min, mean FT calculation time 13 ± 2 min. Intra- and inter-observer variability was good to excellent with an coefficient of reproducibility (CR) ranging 1.6% to 11.5%, and 1.7% to 16.0%, respectively and an intraclass correlation coefficient (ICC) ranging 0.89 to 1.00 and 0.74 to 0.99, respectively. Variability considerably increased in the test-retest setting with a CR ranging 4.2% to 29.1% and an ICC ranging 0.66 to 0.95 in the patient group. Variability was not influenced by level of expertise of the observers. Neither did the presence of myocardial pathology at CMR negatively impact variability. However, compared to global myocardial strain, segmental myocardial strain variability increased with a factor 2-3, in particular for the basal and apical short-axis slices.
  
  
  CONCLUSIONS
  CMR-FT using non-rigid, elastic registration is a reproducible approach for strain analysis in patients routinely scheduled for CMR, and is not influenced by the level of training. However, further improvement is needed to reliably depict small variations in segmental myocardial strain.
authors.affiliation: Lab on Cardiovascular Imaging & Dynamics, Department of Cardiovascular Sciences, KULeuven - University of Leuven, Herestraat 49, Leuven, Belgium.|ICVS/3B's - PT Government Associate Laboratory, Braga/Guimarães, Portugal.|Instituto de Engenharia Mecânica e Gestão Industrial, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal.
authors.forename: Pedro
authors.initials: P
authors.lastname: Morais
authors.affiliation: Department of Imaging and Pathology, KU Leuven - University of Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Alberto
authors.initials: A
authors.lastname: Marchi
authors.affiliation: Department of Imaging and Pathology, KU Leuven - University of Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Bogaert
authors.affiliation: Department of Imaging and Pathology, KU Leuven - University of Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Tom
authors.initials: T
authors.lastname: Dresselaers
authors.affiliation: Lab on Cardiovascular Imaging & Dynamics, Department of Cardiovascular Sciences, KULeuven - University of Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Brecht
authors.initials: B
authors.lastname: Heyde
authors.affiliation: Lab on Cardiovascular Imaging & Dynamics, Department of Cardiovascular Sciences, KULeuven - University of Leuven, Herestraat 49, Leuven, Belgium.
authors.forename: Jan
authors.initials: J
authors.lastname: D'hooge
authors.affiliation: Department of Imaging and Pathology, KU Leuven - University of Leuven, Herestraat 49, Leuven, Belgium. Jan.bogaert@uzleuven.be.
authors.forename: Jan
authors.identifier: http://orcid.org/0000-0001-7495-9183
authors.initials: J
authors.lastname: Bogaert
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000503:physiopathology; D015588:Observer Variation; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013318:Stroke Volume; D013997:Time Factors; D016277:Ventricular Function, Left