The MRI Wound Healing Tool can be used to analyze scratch assays. It measures the area of a wound in a cellular tissue on a stack of images representing a time-series. An example image can be found here. An example image for the find-edges method (see below) can be found here.
To install the tools, drag the link MRI_Wound_Healing_Tool.ijm to the ImageJ launcher window, save it under macros/toolsets in the ImageJ installation and restart ImageJ.
Select the MRI Wound Healing Tool toolset from the >> button of the ImageJ launcher.
By right-clicking on the m button you can open the options dialog.