Most of the machines are limited by staff, not equipment in terms of overall load. They may be fully in use during peak times, but that's mostly because it's convenient to book people for non urgent appointments during the day.

I was in the ER for 14 hours a month ago waiting to see the doctor, but I had my xray within 20 minutes of arriving at triage, and a CT within a half hour of a doctor looking at the xray and deciding I needed more imaging.

It's the same thing with things like operating rooms.