title: Echocardiography without electrocardiogram.
abstract: OBJECTIVE
  automatic detection of the QRS complex on electrocardiogram (ECG) is used on cardiac ultrasound scanners to separate ultrasound image series into cardiac cycles for playback and storage. On small hand-held scanners it is unpractical to connect ECG cables. We therefore aim to do automatic cardiac cycle separation using apical B-mode ultrasound images.
  
  
  RESULTS
  cardiac cycle length is estimated by cyclicity analysis of B-mode intensities. To determine a cycle start estimate near QRS, a deformable model is fitted to the left ventricle in real-time. The model is used to initialize and constrain a speckle tracker positioned near the mitral annulus. In the displacement curve generated by the speckle tracker, a time point near maximum distance from the probe is detected as a cardiac cycle start estimate. Validation against ECG was done on 233 recordings from normal subjects and 46 recordings from subjects with coronary pathology. Several test cases were run for each recording to emulate B-mode series starting at all time points in the cardiac cycle. Totally, 11 886 test cases were run. Cycle length estimation was feasible in 98% of normal subject cases and 91% of pathology cases. Median difference in cycle length by ECG was 0 and -3 ms, respectively. Cycle start estimation was feasible in 90% of normal subject cases and 77% of pathology cases. Median difference to cycle start by ECG was 62 and 76 ms, respectively.
  
  
  CONCLUSIONS
  apical B-mode series can automatically be separated into cardiac cycles without using ECG.
authors.affiliation: Department of Circulation and Medical Imaging, Faculty of Medicine, Norwegian University of Science and Technology, Postboks 8905, Medisinsk teknisk forskningssenter, NO-7491 Trondheim, Norway.
authors.forename: Svein Arne
authors.initials: SA
authors.lastname: Aase
authors.forename: Sten Roar
authors.initials: SR
authors.lastname: Snare
authors.forename: Håvard
authors.initials: H
authors.lastname: Dalen
authors.forename: Asbjørn
authors.initials: A
authors.lastname: Støylen
authors.forename: Fredrik
authors.initials: F
authors.lastname: Orderud
authors.forename: Hans
authors.initials: H
authors.lastname: Torp
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D004452:Echocardiography / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D006331:Heart Diseases / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D012815:Signal Processing, Computer-Assisted