I want to trace the outline of a radio-opaque bolus during swallowing in video fluoroscope images. Normally I would use ImageJ on a PC for such a problem, but this will require a touchscreen tablet computer and stylus. I'm hoping to use my Ipad for this data collection, but I'm not aware of any app that could trace an image, and then allow calculation/measurement of area enclosed by the tracing, the length of the tracing line, darkness of the pixels enclosed, and so on. Or alternatively, an app that allows the tracing data to be exported, and then I could find some other program to do the calculations. Any ideas?