Computer automated diaphragm motion quantification in a fluoroscopic movie

We report on the development and evaluation of a computer program which automatically tracks the respiratory motion of the diaphragm in fluoroscopic movies. The program is based upon a variant of the active contour algorithm, and requires minimal user initialization. Resolution and iso-center position are automatically extracted from the cross hairs and graticule tray points. The program processes fluoroscopic movies at a rate of 2 frames per second, and displays results both on the image and in graphical form. At each frame of the fluoroscopic movie, the contour locates the position of the diaphragm by minimizing the value of its energy function. The energy function acts to steer the contour to intensity gradients of interest, while penalizing deviation from a reference shape. The shape constraints are formulated to allow for a deformation of the diaphragm, while excluding spurious intensity gradients. A comparison of automated tracking with manual determination of diaphragm positions shows the algorithm to be highly reliable. Mean difference between automatic and manual methods is 1.3 mm, with standard deviation of 0.6 mm. The small systematic offset results from the manually observed superior extent of the diaphragm being slightly superior to the point of maximum intensity gradient. We conclude that computer automated determination of diaphragm position in fluoroscopic movies is a viable replacement for manual inspection