Ever have one of those problems where the more you dig into it to find a solution, the more complicated it becomes?
A couple of days ago, I started digging into a problem we were having with one of our computed radiography (CR) readers. Techs were complaining that they were starting to have to use much higher x-ray techniques than normal to get properly exposed images. So, I head over, and run some quick checks with some of my test objects, and narrow it down to the CR reader. Sure enough, the reader in question was producing a lower exposure index (a number that's related to how much radiation the CR plate was exposed to) than an older CR reader next to it.
The next day, I head over there with some more test objects to get some more quantitative data, and confirmed just how much lower the CR reader was responding.
Today, I decided I had better check our other CR readers. They were all relatively new (installed April 2003), and I had data for some of them when they were first installed. The testing is something I usually try to do on a monthly basis, but the summer was a pretty busy one, so I hadn't been able to get to doing my regular tests on them. Much to my surprise, I found all of the other CR readers producing lower exposure index values too. And to make it worse, they were all lower by the same amount. Each of the CR readers runs a set of diagnostics periodically on various systems, which is very useful. A quick check of those results didn't reveal anything significantly wrong that I thought would cause the problem though. So now, instead of trying to figure out what the problem with one unit is, I have to figure out what could be causing the same problem on 5 different units. Could it be the laser assembly? The light guide? A photomultiplier tube?
At first my guess was the laser starting to fail. But how does it happen to 5 different units by the same amount? A bad batch of lasers perhaps? Who knows. The more I dig into it, the more perplexing the problem becomes.