Please be more specific. You want to get the value of each pixel into Excel AFTER a threshold? You will only get either 0 or 255, but perhaps I have misunderstood.
To get all the pixel intensities as long as you're not interested in their locations, the simplest you can do is to grab the histogram of the image through "Analyze > Histogram" then use the "Copy" button.
You can then do some statistics in excel.
If you want to keep the locations of the pixels as well, you can save your image as text using "Save As... > Text Image"
Without further explanations, we are unfortunately unable to help you more.