Parallel Raster Scan for Euclidean Distance Transform

Distance transform (DT) and Voronoi diagrams (VDs) have found many applications in image analysis. Euclidean distance transform (EDT) can generate forms that do not vary with the rotation, because it is radially symmetrical, which is a desirable characteristic in distance transform applications. Recently, parallel architectures have been very accessible and, particularly, GPU-based architectures are very promising due to their high performance, low power consumption and affordable prices. In this paper, a new parallel algorithm is proposed for the computation of a Euclidean distance map and Voronoi diagram of a binary image that mixes CUDA multi-thread parallel image processing with a raster propagation of distance information over small fragments of the image. The basic idea is to exploit the throughput and the latency in each level of memory in the NVIDIA GPU; the image is set in the global memory, and can be accessed via texture memory, and we divide the problem into blocks of threads. For each block we copy a portion of the image and each thread applies a raster scan-based algorithm to a tile of m×m pixels. Experiment results exhibit that our proposed GPU algorithm can improve the efficiency of the Euclidean distance transform in most cases, obtaining speedup factors that even reach 3.193.

High-Throughput Segmentation of Tiled Biological Structures using Random-Walk Distance Transforms

Various 3D imaging techniques are routinely used to examine biological materials, the results of which are usually a stack of grayscale images. In order to quantify structural aspects of the biological materials, however, they must first be extracted from the dataset in a process called segmentation. If the individual structures to be extracted are in contact or very close to each other, distance-based segmentation methods utilizing the Euclidean distance transform are commonly employed. Major disadvantages of the Euclidean distance transform, however, are its susceptibility to noise (very common in biological data), which often leads to incorrect segmentations (i.e., poor separation of objects of interest), and its limitation of being only effective for roundish objects. In the present work, we propose an alternative distance transform method, the random-walk distance transform, and demonstrate its effectiveness in high-throughput segmentation of three microCT datasets of biological tilings (i.e., structures composed of a large number of similar repeating units). In contrast to the Euclidean distance transform, the random-walk approach represents the global, rather than the local, geometric character of the objects to be segmented and, thus, is less susceptible to noise. In addition, it is directly applicable to structures with anisotropic shape characteristics. Using three case studies—tessellated cartilage from a stingray, the dermal endoskeleton of a starfish, and the prismatic layer of a bivalve mollusc shell—we provide a typical workflow for the segmentation of tiled structures, describe core image processing concepts that are underused in biological research, and show that for each study system, large amounts of biologically-relevant data can be rapidly segmented, visualized, and analyzed.

Identification of protein pockets and cavities by Euclidean Distance Transform

Protein pockets and cavities usually coincide with the active sites of biological processes, and their identification is significant since it constitutes an important step for structure-based drug design and protein-ligand docking applications. This research presents PoCavEDT, an automated purely geometric technique for the identification of binding pockets and occluded cavities in proteins based on the 3D Euclidean Distance Transform. Candidate protein pocket regions are identified between two Solvent-Excluded surfaces generated with the Euclidean Distance Transform using different probe spheres, which depend on the size of the binding ligand. The application of simple, yet effective geometrical heuristics ensures that the proposed method obtains very good ligand binding site prediction results. The method was applied to a representative set of protein-ligand complexes and their corresponding unbound protein structures to evaluate its ligand binding site prediction capabilities. Its performance was compared to the results achieved with several purely geometric pocket and cavity prediction methods, namely SURFNET, PASS, CAST, LIGSITE, LIGSITECS, PocketPicker and POCASA. Success rates PoCavEDT were comparable to those of POCASA and outperformed the other software.

Identification of protein pockets and cavities by Euclidean Distance Transform

Protein pockets and cavities usually coincide with the active sites of biological processes, and their identification is significant since it constitutes an important step for structure-based drug design and protein-ligand docking applications. This research presents PoCavEDT, an automated purely geometric technique for the identification of binding pockets and occluded cavities in proteins based on the 3D Euclidean Distance Transform. Candidate protein pocket regions are identified between two Solvent-Excluded surfaces generated with the Euclidean Distance Transform using different probe spheres, which depend on the size of the binding ligand. The application of simple, yet effective geometrical heuristics ensures that the proposed method obtains very good ligand binding site prediction results. The method was applied to a representative set of protein-ligand complexes and their corresponding unbound protein structures to evaluate its ligand binding site prediction capabilities. Its performance was compared to the results achieved with several purely geometric pocket and cavity prediction methods, namely SURFNET, PASS, CAST, LIGSITE, LIGSITECS, PocketPicker and POCASA. Success rates PoCavEDT were comparable to those of POCASA and outperformed the other software.