Constraint factor graph cut–based active contour method for automated cellular image segmentation in RNAi screening

Image‐based, high throughput genome‐wide RNA interference (RNAi) experiments are increasingly carried out to facilitate the understanding of gene functions in intricate biological processes. Automated screening of such experiments generates a large number of images with great variations in image quality, which makes manual analysis unreasonably time‐consuming. Therefore, effective techniques for automatic image analysis are urgently needed, in which segmentation is one of the most important steps. This paper proposes a fully automatic method for cells segmentation in genome‐wide RNAi screening images. The method consists of two steps: nuclei and cytoplasm segmentation. Nuclei are extracted and labelled to initialize cytoplasm segmentation. Since the quality of RNAi image is rather poor, a novel scale‐adaptive steerable filter is designed to enhance the image in order to extract long and thin protrusions on the spiky cells. Then, constraint factor GCBAC method and morphological algorithms are combined to be an integrated method to segment tight clustered cells. Compared with the results obtained by using seeded watershed and the ground truth, that is, manual labelling results by experts in RNAi screening data, our method achieves higher accuracy. Compared with active contour methods, our method consumes much less time. The positive results indicate that the proposed method can be applied in automatic image analysis of multi‐channel image screening data.     

An analytical model for the prediction of temperature distribution and evolution in hybrid laser-waterjet micro-machining

A hybrid laser-waterjet micro-machining technology was developed for near damage-free micro-ablation recently. It uses a new material removal concept where the laser-softened material is expelled by a pressurised waterjet. The temperature field in this hybrid machining process is an essential quantity for understanding the underlying material removal mechanism and optimizing the process conditions. This study presents a three-dimensional (3-D) analytical model for the temperature field in this hybrid laser-waterjet micro-machining process. The interaction among the laser, waterjet, and workpiece is considered in the model. The absorption of laser by water, the formation of laser-induced plasma in water, the bubble formation and the laser refraction at the air-water interface are discussed. DuHamel’s principle is used to determine a closed-form temperature equation and a solution in a variable separation form is obtained. A calculation for silicon carbide is conducted. The results are illustrated by a group of 3-D temperature profiles intuitively and visually. It is shown that the temperatures are below the melting point during the process due to the cooling action of waterjet. The almost damage-free micro-machining can be achieved. Besides, the maximum temperature increases with the increased average laser power and waterjet offset distance and decreased nozzle exit diameter where the average laser power takes a major action.