[How to convert mds to iso?]

it's a DVD9 img which is a mds/mdf file about 8GB

since i want to convert it to iso

that was a error msg show up,

"File size exceeds the limit imposed by the ISO9660 file system"

i used another software b4 but the result is the iso just about 4GB

i think it just convert the first layer from the mds/mdf but not include the second one

 

is it another file system for dual layer iso file??

or I need to set something to make it as a dual layer iso file?

I hope someone help me to solve this problems,thz a lot