title: Rapid automatic segmentation of abnormal tissue in late gadolinium enhancement cardiovascular magnetic resonance images for improved management of long-standing persistent atrial fibrillation.
abstract: BACKGROUND
  Atrial fibrillation (AF) is the most common heart rhythm disorder. In order for late Gd enhancement cardiovascular magnetic resonance (LGE CMR) to ameliorate the AF management, the ready availability of the accurate enhancement segmentation is required. However, the computer-aided segmentation of enhancement in LGE CMR of AF is still an open question. Additionally, the number of centres that have reported successful application of LGE CMR to guide clinical AF strategies remains low, while the debate on LGE CMR's diagnostic ability for AF still holds. The aim of this study is to propose a method that reliably distinguishes enhanced (abnormal) from non-enhanced (healthy) tissue within the left atrial wall of (pre-ablation and 3 months post-ablation) LGE CMR data-sets from long-standing persistent AF patients studied at our centre.
  
  
  METHODS
  Enhancement segmentation was achieved by employing thresholds benchmarked against the statistics of the whole left atrial blood-pool (LABP). The test-set cross-validation mechanism was applied to determine the input feature representation and algorithm that best predict enhancement threshold levels.
  
  
  RESULTS
  Global normalized intensity threshold levels T PRE  = 1 1/4 and T POST  = 1 5/8 were found to segment enhancement in data-sets acquired pre-ablation and at 3 months post-ablation, respectively. The segmentation results were corroborated by using visual inspection of LGE CMR brightness levels and one endocardial bipolar voltage map. The measured extent of pre-ablation fibrosis fell within the normal range for the specific arrhythmia phenotype. 3D volume renderings of segmented post-ablation enhancement emulated the expected ablation lesion patterns. By comparing our technique with other related approaches that proposed different threshold levels (although they also relied on reference regions from within the LABP) for segmenting enhancement in LGE CMR data-sets of AF patients, we illustrated that the cut-off levels employed by other centres may not be usable for clinical studies performed in our centre.
  
  
  CONCLUSIONS
  The proposed technique has great potential for successful employment in the AF management within our centre. It provides a highly desirable validation of the LGE CMR technique for AF studies. Inter-centre differences in the CMR acquisition protocol and image analysis strategy inevitably impede the selection of a universally optimal algorithm for segmentation of enhancement in AF studies.
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. A.Giannakidis@rbht.nhs.uk.|National Heart and Lung Institute, Imperial College London, London, UK. A.Giannakidis@rbht.nhs.uk.
authors.forename: Archontis
authors.initials: A
authors.lastname: Giannakidis
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. E.Nyktari@rbht.nhs.uk.
authors.forename: Eva
authors.initials: E
authors.lastname: Nyktari
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. J.Keegan@rbht.nhs.uk.|National Heart and Lung Institute, Imperial College London, London, UK. J.Keegan@rbht.nhs.uk.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Keegan
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. I.Pierce@rbht.nhs.uk.|National Heart and Lung Institute, Imperial College London, London, UK. I.Pierce@rbht.nhs.uk.
authors.forename: Iain
authors.initials: I
authors.lastname: Pierce
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. I.SumanHorduna@rbht.nhs.uk.
authors.forename: Irina
authors.initials: I
authors.lastname: Suman Horduna
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. S.Haldar@rbht.nhs.uk.
authors.forename: Shouvik
authors.initials: S
authors.lastname: Haldar
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. DJ.Pennell@rbht.nhs.uk.|National Heart and Lung Institute, Imperial College London, London, UK. DJ.Pennell@rbht.nhs.uk.
authors.forename: Dudley J
authors.initials: DJ
authors.lastname: Pennell
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. R.Mohiaddin@rbht.nhs.uk.
authors.forename: Raad
authors.initials: R
authors.lastname: Mohiaddin
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. T.Wong2@rbht.nhs.uk.
authors.forename: Tom
authors.initials: T
authors.lastname: Wong
authors.affiliation: Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK. D.Firmin@rbht.nhs.uk.|National Heart and Lung Institute, Imperial College London, London, UK. D.Firmin@rbht.nhs.uk.
authors.forename: David N
authors.initials: DN
authors.lastname: Firmin
mesh_terms: D055011:Ablation Techniques; D000465:Algorithms; D001281:Atrial Fibrillation / Q000175:diagnosis* / Q000473:pathology* / Q000628:therapy; D001331:Automation; D003287:Contrast Media; D005260:Female; D005682:Gadolinium; D006325:Heart Atria / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation
chemical_list: D003287:Contrast Media; D005682:Gadolinium