Pranav Bhagirath

55 Evaluation of state-of-the-art segmentation algorithms for left ventricle infarct from late Gadolinium enhancement MR images weight. This enforced coherence in the segmentation output. The final segmentation was obtainedusingglobal optimizationover the entire image.This allowed for disjointed infarct regions to be identified in the image. Algorithm evaluation Reference standard: consensus ground truth, a reference standard for scar in each case was obtained by combining volumetric segmentations from three separate observers. All observers were cardiologists with several years’ experience in CMR assessment of LV function and tissue viability. They also had several years’ experience working with patients suffering from ischemic heart diseases. For both datasets, they were blinded to the underlying clinical situation of patients and pigs. For pigs, lesions were obtained by occluding either the left-anterior descending or left-circumflex artery, and the observers were blinded to this fact. The observers were not instructed to look for areas of grey zones. For regions affected by microvascular obstructions, they were instructed to avoid these by looking for regions of significant hypo-enhancement surrounded by enhanced regions. Scars in the imageswere segmentedas follows: (1) Each slice in the LGECMRwas analyzed separately in the short-axis view. The segmentation of themyocardiumwas loaded as an overlay. (2) The basal, mid and apical slices were identified along with the LV orientation, i.e. the posterior and anterior ends. (3) The short-axis slices were then analyzed one at a time sequentially from basal to apical or apical to basal. (4) The basal slices were then examined for non-scar related enhancements (see Turkbey et al., 2012) such as the right ventricle (RV) insertion point, and partial voluming in the basal slices due to the outflow tract and appendage. The mid and apical slices were also examined for coronary arteries carrying blood that could be enhanced, and microvascular obstructions. (5) Pixels enhanced within myocardiumwere labeled as scar and generally noisy pixels or regions were avoided. Noise observed in the lungs was used as a reference. Each observer was provided with the same set of guidelines as above. However, their segmentations differed in some instances. This was generally due to differences in their opinion and experience. Such inter-observer variability is now widely accepted. It was thus important to merge the segmentations and obtain a consensus ground truth. A maximum likelihood estimation of ground truth was obtained using a published algorithm known as the STAPLE (Warfield et al., 2004). For every voxel, a probabilistic estimate of the true segmentation was computed using an optimal combination of