Tracking rolling leukocytes in vivo using active contours with motion gradient vector flow

Studying the behavior of rolling leukocytes in vivo is important as the study can reveal clues about the causes of inflammatory disease. Typically such studies require tracking tens of thousands of leukocytes every day for clinical trials and drug discovery. Thus an important image processing task is to automatically track the rolling leukocytes from intravital microscopic videos. In this research an active contour or snake based method for leukocyte tracking is proposed. The proposed active contour model exploits shape and size constraints suitable for tracking the leukocytes. The experiments reveal that the shape and size constraints play an indispensable role in the tracking task. The a priori leukocyte motion direction information is imbedded into a vector field that acts as an external force for the active contour. The experiments also demonstrate that the addition of the proposed force field can take care of both slowly and fast rolling leukocytes and enhances the snake tracker performance. The construction of the vector field is accomplished by first realizing an energy functional involving the motion direction, and the image gradient magnitude, then minimizing this functional through variational principles. Further, we propose inclusion filters, a class of self-dual contrast invariant connected operators. Our experiments show that prefiltering the video frames with inclusion filters enhances the tracking performance. The test data sets for the tracking experiments are comprised of (a) 100 intravital microscopic video sequences each 91 frames long (3-second duration at 30 frames per second) and (b) 25 intravital microscopic video sequences each 31 frames long (1-second duration). All tracking experiments are performed on data set (a) including the manual data collection for tracking performance comparison. Comparison of numerical performances with two standard tracking techniques (centroid and correlation) is also provided. To illustrate the efficacy of the proposed tracking method for fast rolling leukocytes, the test data set (b) is utilized.