<html> <head> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> </head> <body text="#000000" bgcolor="#FFFFFF"> <div class="moz-forward-container"> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> Hallo Gate users, I have a small simple question regarding defining the lesion-to-background ratios in Gate. Assume that I have an activity concentration of the background, lets say 16.9 Bq/mL with an activity amount of 100 MBq and volume of 5892857 mL (cylinder size of 500 mm). Now I would like to define a hot insert of 13 mm inside the 500 mm active background with a Lesion-to-Background ratio (0.7:1). does anyone know how I can calculate the activity for the 13 mm lesion size for the ratio (0.7:1). Thanks alot for your help. regards, Bassim </div> </body> </html>