Imatest IT uses the Matlab runtime library which is a single-threaded routine that is not thread-safe.
If your tester application uses multiple threads, you should restrict all the parts that call upon the Imatest library to a single thread.
If your tester application uses multiple processes be careful about using busy waiting in order to check for the results of the test to occur. Without a sleep statement inside your loop, the rapidly looping process will prevent context switching to other processes, which will prevent them from running and consume a large amount of CPU resources causing both processes to freeze.
If you want to run multiple processes with Imatest calculations, please see: