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If you saved the Image as a .is2 format it will have all the radiometric data and you can export that data.
Below is a screen shot highlighting a .is2 file and to export that data click on the Export Icon circled in red see below picture. 
The picture below the first picture is the window that pops up when you click on the Export Icon. Make sure to click on the Temperature Data Icon circled in red. The format .csv is compatible with Excel. 
Click on the Continue box at the bottom of that window to Export the .csv file.