Determining the start and end of a dCT signal within an EIT signal

I have a Electrical Impedance Tomography(EIT) signal during wich a dynamic Computed Tomography(dCT) scan is made.

The signal looks like this :

So basically I want to determine the start and end time of the dCT measurement. The signal power doesent seem to change, so I decided I should find the peak to peak intervals and make some kind of a decision based on that, as it can be seen from the picture the peak to peak intervals decrease in the region where the dCT scan is expected to be.

Does that make any sense, or is there another way to do the same thing?