title: Measurements of the left atrium and pulmonary veins for analysis of reverse structural remodeling following cardiac ablation therapy.
abstract: OBJECTIVE
  Geometric analysis of the left atrium and pulmonary veins is important for assessing reverse structural remodeling following cardiac ablation therapy. Most volumetric analysis techniques, however, require laborious manual tracing of image cross-sections. Pulmonary vein diameters are typically measured at the junction between the left atrium and pulmonary veins, called the pulmonary vein ostia, with manually drawn lines on volume renderings or in image slices. In this work, we describe a technique for making semi-automatic measurements of left atrial volume and pulmonary vein diameters from high resolution CT scans and demonstrate its use for analyzing reverse structural remodeling following cardiac ablation therapy.
  
  
  METHODS
  The left atrium and pulmonary veins are segmented from high-resolution computed tomography (CT) volumes using a 3D volumetric approach and cut planes are interactively positioned to separate the pulmonary veins from the body of the left atrium. Left atrial volume and pulmonary vein ostial diameters are then automatically computed from the segmented structures. Validation experiments are conducted to evaluate accuracy and repeatability of the measurements. Accuracy is assessed by comparing left atrial volumes computed with the proposed methodology to a manual slice-by-slice tracing approach. Repeatability is assessed by making repeated volume and diameter measurements on duplicated and randomized datasets. The proposed techniques were then utilized in a study of 21 patients from the Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation Trial (CABANA) pilot study who were scanned both before and approximately 3 months following ablation therapy.
  
  
  RESULTS
  In the high resolution CT scans the left atrial volume measurements show high accuracy with a mean absolute difference of 2.3±1.9 cm(3) between volumes computed with the proposed methodology and a manual slice-by-slice tracing approach. In the intra-rater repeatability study, the mean absolute difference in left atrial volume was 4.7±2.5 cm(3) and 4.4±3.4 cm(3) for the two raters. Intra-rater repeatability for pulmonary vein diameters ranged from 0.9 to 2.3 mm. The inter-rater repeatability for left atrial volume was 5.8±5.1 cm(3) and inter-rater repeatability for pulmonary vein diameter measurements ranged from 1.4 to 2.3 mm. In the patient study, significant (p<.05) decreases in left atrial volume and all four pulmonary vein diameters were observed. The absolute change in LA volume was 20.0 cm(3), 95%CI [12.6, 27.5]. The left inferior pulmonary vein diameter decreased 2.1 mm, 95%CI [0.4, 3.7], the left superior pulmonary vein diameter decreased 3.2 mm, 95%CI [1.0, 5.4], the right inferior pulmonary vein diameter decreased 1.5 mm, 95%CI [0.3, 2.7], and the right superior pulmonary vein diameter decreased 2.8 mm, 95%CI [1.4, 4.3].
  
  
  CONCLUSIONS
  Using the proposed techniques, we demonstrate high accuracy of left atrial volume measurements as well as high repeatability for left atrial volume and pulmonary vein diameter measurements. Following cardiac ablation therapy, a significant decrease was observed for left atrial volume as well as all four pulmonary vein diameters.
authors.affiliation: Biomedical Imaging Resource, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Maryam E
authors.initials: ME
authors.lastname: Rettmann
authors.affiliation: Biomedical Imaging Resource, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: David R
authors.initials: DR
authors.lastname: Holmes
authors.affiliation: Department of Radiology, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Jerome F
authors.initials: JF
authors.lastname: Breen
authors.affiliation: Biomedical Imaging Resource, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Xin
authors.initials: X
authors.lastname: Ge
authors.affiliation: Biomedical Imaging Resource, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Karwoski
authors.affiliation: Division of Cardiovascular Diseases, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Kristi H
authors.initials: KH
authors.lastname: Monahan
authors.affiliation: Duke Center for Atrial Fibrillation, Duke University Medical Center; Division of Cardiac Electrophysiology, Department of Medicine, Duke University, Durham, NC 27708, United States.
authors.forename: Tristram D
authors.initials: TD
authors.lastname: Bahnson
authors.affiliation: Division of Cardiovascular Diseases, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Packer
authors.affiliation: Biomedical Imaging Resource, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Robb
mesh_terms: D001281:Atrial Fibrillation / Q000628:therapy; D017115:Catheter Ablation; D006325:Heart Atria / Q000033:anatomy & histology*; D006801:Humans; D011667:Pulmonary Veins / Q000033:anatomy & histology*
keywords: Atrial fibrillation; Cardiac ablation therapy; Left atrial segmentation; Left atrial volume; Left atrium; Pulmonary vein diameter