You may want to look into using Image resizer instead to begin with and only store the original image.
The advantage to that is that you don't have to limit yourself to one of 4 images like your current implementation. If later you decided you wanted a 200px version or a 185px version you would be stuck with a complex update of your database and existing records, but with image resizer you just change the size on the page and the rest of the work is done for you.
Here is a video that talks about how image resizer works: watch?v=FzQO0EX8A9I
Anyway if you wanted just that portion of the image you would probably have to parse it out:
<?php echo(substr($test,0,strrpos($WA_DFP_UploadStatus["WA_UploadResult1"]["serverFileName"],"_"))); ?>
That would give you everything up to the last underscore in the server file name, which I think would work for what you are trying to do.