How to use ImageJ FFT to measure interval disance

Hi all:
I’m new for using the ImageJ. I want to measure the mean interval distance of the cellular actin filment in the direction perpendicular to the mean oirentation angle by using the Image J FFT function. I have got the FFT result. But I don’t know how to get the interval distance information from blur-like FFT results. Anyone tell me how to deal with it. Thanks a lot.
actin FFT