title: Using a respiratory navigator significantly reduces variability when quantifying left ventricular torsion with cardiovascular magnetic resonance.
abstract: BACKGROUND
  Left ventricular (LV) torsion is an important indicator of cardiac function that is limited by high inter-test variability (50% of the mean value). We hypothesized that this high inter-test variability is partly due to inconsistent breath-hold positions during serial image acquisitions, which could be significantly improved by using a respiratory navigator for cardiovascular magnetic resonance (CMR) based quantification of LV torsion.
  
  
  METHODS
  We assessed respiratory-related variability in measured LV torsion with two distinct experimental protocols. First, 17 volunteers were recruited for CMR with cine displacement encoding with stimulated echoes (DENSE) in which a respiratory navigator was used to measure and then enforce variability in end-expiratory position between all LV basal and apical acquisitions. From these data, we quantified the inter-test variability of torsion in the absence and presence of enforced end-expiratory position variability, which established an upper bound for the expected torsion variability. For the second experiment (in 20 new, healthy volunteers), 10 pairs of cine DENSE basal and apical images were each acquired from consecutive breath-holds and consecutive navigator-gated scans (with a single acceptance position). Inter-test variability of torsion was compared between the breath-hold and navigator-gated scans to quantify the variability due to natural breath-hold variation. To demonstrate the importance of these variability reductions, we quantified the reduction in sample size required to detect a clinically meaningful change in LV torsion with the use of a respiratory navigator.
  
  
  RESULTS
  The mean torsion was 3.4 ± 0.2°/cm. From the first experiment, enforced variability in end-expiratory position translated to considerable variability in measured torsion (0.56 ± 0.34°/cm), whereas inter-test variability with consistent end-expiratory position was 57% lower (0.24 ± 0.16°/cm, p < 0.001). From the second experiment, natural respiratory variability from consecutive breath-holds translated to a variability in torsion of 0.24 ± 0.10°/cm, which was significantly higher than the variability from navigator-gated scans (0.18 ± 0.06°/cm, p = 0.02). By using a respiratory navigator with DENSE, theoretical sample sizes were reduced from 66 to 16 and 26 to 15 as calculated from the two experiments.
  
  
  CONCLUSIONS
  A substantial portion (22-57%) of the inter-test variability of LV torsion can be reduced by using a respiratory navigator to ensure a consistent breath-hold position between image acquisitions.
authors.affiliation: Department of Electrical and Computer Engineering, University of Kentucky, Lexington, KY, USA.|Department of Pediatrics, University of Kentucky, Lexington, KY, USA.
authors.forename: Sean M
authors.initials: SM
authors.lastname: Hamlet
authors.affiliation: Department of Pediatrics, University of Kentucky, Lexington, KY, USA.|Department of Imaging Science and Innovation, Geisinger Health System, Danville, PA, USA.|Biomedical and Translational Informatics Institute, Geisinger Health System, Danville, PA, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Haggerty
authors.affiliation: Department of Pediatrics, University of Kentucky, Lexington, KY, USA.|Department of Imaging Science and Innovation, Geisinger Health System, Danville, PA, USA.|Biomedical and Translational Informatics Institute, Geisinger Health System, Danville, PA, USA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Suever
authors.affiliation: Department of Pediatrics, University of Kentucky, Lexington, KY, USA.|Department of Biomedical Engineering, University of Kentucky, Lexington, KY, USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Wehner
authors.affiliation: Department of Pediatrics, University of Kentucky, Lexington, KY, USA.
authors.forename: Kristin N
authors.initials: KN
authors.lastname: Andres
authors.affiliation: Department of Biomedical Engineering, University of Kentucky, Lexington, KY, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Powell
authors.affiliation: Departments of Biostatistics and Statistics, University of Kentucky, Lexington, KY, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Charnigo
authors.affiliation: Department of Pediatrics, University of Kentucky, Lexington, KY, USA. bkf@gatech.edu.|Department of Imaging Science and Innovation, Geisinger Health System, Danville, PA, USA. bkf@gatech.edu.|Biomedical and Translational Informatics Institute, Geisinger Health System, Danville, PA, USA. bkf@gatech.edu.|Department of Biomedical Engineering, University of Kentucky, Lexington, KY, USA. bkf@gatech.edu.|Departments of Physiology and Medicine, University of Kentucky, Lexington, KY, USA. bkf@gatech.edu.|Department of Radiology, Geisinger Health System, 100 North Academy Avenue, Danville, PA, 17822-4400, USA. bkf@gatech.edu.
authors.forename: Brandon K
authors.initials: BK
authors.lastname: Fornwalt
mesh_terms: D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D062485:Breath Holding; D005260:Female; D064368:Healthy Volunteers; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D019028:Magnetic Resonance Imaging, Cine; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D055425:Respiratory-Gated Imaging Techniques; D013997:Time Factors; D054159:Torsion, Mechanical; D016277:Ventricular Function, Left; D055815:Young Adult
keywords: Breath-holds; Cardiovascular magnetic resonance; DENSE; Left ventricular torsion; Respiratory navigator gating