One good way to do this as well as show a number of other time periods (ex. Prior 2 quarters, Year to date, prior year to date, etc.) is to build a calendar table into the data model. There are a number of good examples of calendar tables to reuse, if you need them.
There are other ways to solve this without changing the data model, including:
1. Adding set analysis to each expression in the chart to limit the data to the periods you want.
2. Creating a calculated dimension that is null for all values other than the 12 periods.
I generally prefer the calendar table, over the set analysis and both over the calculated dimension.
I hope that helps.
Here is one that I recently used and you may find helpful - Fiscal Calendar Table load script
This sample script uses a couple features that you may not need, so just pull those out if you like.
I'm sure there are other good examples that will work for you as well.
Please let me know how this turns out for you.