  We present a method for unsupervised segmentation of echocardiograms (echo).
The method uses an iterative Dijkstra's algorithm, a strategic node selection,
and a novel cost matrix formulation based on intensity peak prominence and is
thus termed the "Prominence Iterative Dijkstra's" algorithm, or ProID. Although
the current analysis focuses on the left ventricle (LV), ProID is applicable to
all four heart chambers. ProID was tested using artificial echo images
representing five different systems. Results showed accurate LV contours and
volume estimations as compared to the ground-truth for all systems.
Subsequently, ProID was used to analyze a clinical cohort of 66 pediatric
patients, including both normal and diseased hearts. Output segmentations,
end-diastolic, end-systolic volumes, and ejection fraction (EF) were compared
against manual segmentations from two expert readers. ProID maintained an
average Dice similarity score of 0.93 when comparing against manual
segmentation. Comparing the two expert readers, the manual segmentations
maintained a score of 0.93, which increased to 0.95 when they used ProID. Thus,
ProID successfully reduced the inter-operator variability across the two expert
readers. Overall, this work demonstrates that ProID yields accurate boundaries
across all age groups, disease states, and echo platforms with low computation
cost, thereby establishing its clinical usefulness.
