Finding all reviews that have an artifact in them

Hi.  I'm trying to use the REST API to find all reviews that have a particular artifact in them.  If I use the command-line client to get the review in XML format, I'm looking for the string that is in the <artifacts> section, in <artifact>, then <path>.  But basically, I'd be happy if I could search by the full path of the artifact and get all reviews that have string in the Artifacts (or the "review materials" - "changes from Git").  I'd further like to reduce it to reviews that match a string in the custom field.

I've searched through the documentation but so far have not been able to find anything that lets me do this programmatically.  I know I can do it from the web GUI but I really need to have my program be able to ask Collaborator for the reviews that match this criteria.  Is there any way to do this?  Even if the list is a bit overly broad I can get each review and search it but I'm trying to reduce the number of reviews I ask for as that is a very time-consuming task.

Thanks...

Brian