I have worked in a hospital and in a centralized scanning facility and the metrics were a little different in both facilities. The scanning center we had 8 hospitals that we scanned for with 4 different EHRs. At the hospital that I was at it was a little easier because we only had one EHR to deal with. We had metrics in place for prepping, scanning, indexing, quality, analysis.
In the hospital I was at we worked our metrics off pages per hour, and had staff enter they numbers daily into a POB system that our facility was also using for the coding team. We just made some changes so that we could use it for the teams that we wanted to.
The scanning center I worked for we based metrics off of inches and weight per hour. The team would have to measure and weigh their work each night. Then we built a macro that they would enter their numbers in each night and then it would be sent to the team after they completed it.