Transmission electron microscopy images of beta islet cells contain many complex structures, making it difficult to accurately segment insulin granule cores. Quantification of sub cellular structures will allow biologists to better understand cellular mechanics. Two novel, level set active contour models are presented in this paper. The first utilizes a shape regularizer to reduce oversegmentation. The second contribution is a dual active contour, which achieves accurate core segmentations. The segmentation algorithm proceeds through three stages: an initial rough segmentation using the first contribution, cleaning using morphological techniques and a refining step using the proposed dual active contour. Our method is validated on a set of manually defined ground truths.