How can I get the real Path from a Macro Path like $(TargetDir)?

In a t4 text template I'm trying to load a dll using: Assembly.LoadFile(dllPath).

But it returns me the error: Absolute Path information is required.

The dll path is: var dllPath = "$(TargetDir)Project.dll" or $(SolutionDir)Project\\bin\\debug\\Project.dll.

How can I transform "$(TargetDir)Project.dll" in his truly form "C:\Users\....\Project.dll" before send it to Assembly.LoadFile.