Response time for loading image problem

Response time of loading image is varying significantly, why is this happening & how can is solve this. Please consider the following senario :

1st iteration

Say when i am loading a image file in word application for the first time it takes about 12sec. But when i am loading the image file (without closing the application) for the second time it takes 6 sec.

Second iteration

Then i am closing my word application & when i am loading the same image it takes 6 sec. For the second time it loads in 6 sec.

What i am thinking is that when application closes it release all the memory it开发者_JAVA百科 posses. But in second iteration it is not happening because it loads the image in 6sec(both times).

Why this is happening & how ?

Please suggest