Category: Work stuff

Did the acceptance testing of our first digital radiography unit a couple of days ago, a GE Revolution XR/d.

As imaging technology changes, I usually have to adapt my testing methods to fit. Some technologies render certain tests obsolete or irrelevant while other tests need to be modified, or the analysis changed. In the past, I’ve had to modify my test and analysis procedures for CR units and more recently multi-detector CT scanners.

This new DR unit was no exception. Being a digital unit, a few things went a little faster and easier. Images pop up within 15 seconds of the exposure, so a lot of time gets cut out waiting for the images to appear. The table detector is electronically coupled to the location of the tube and slides along as you move the tube along the table, so no need to fuss with centering the tube over the detector. The folks at GE were even kind enough to incorporate a patient entrance dose display and cumulative exposure counter on the workstation. For some reason though, they’ve apparently decided to forego any kind of exposure index indicator – some kind of indicator to the technologist that the x-ray exposure they just made falls within an acceptable range for image quality. At least there wasn’t one that I could find or that the service engineer knew about.

An exposure index is a very useful tool for providing feedback to the technologist. With conventional film/screen, the tech can easily see whether the exposure was too much or too little by how dark the developed film comes out. With digital imaging, there’s no relationship between the appearance of the image and exposure adequacy except in the appearance of noise. Almost all CR manufacturers have some form of exposure index that’s displayed to the tech. I’m puzzled as to why this GE DR unit doesn’t have anything. Maybe I’ll just have to dig deeper to find it.

The first problem this caused was just how to test the kV and thickness tracking for the phototimer. The phototimer is responsible for making sure the image receptor (film, CR cassette, DR receptor) gets enough radiation to produce an adequate image. For film, you measure the optical density (OD). With CR, I use whatever exposure index is provided by the CR vendor as an analog for OD. With this GE DR unit, there wasn’t anything immediately obvious to use. So after a bit of mucking around with the software to see what I could find, I eventually ended up using a central region of interest to get the mean pixel value from the raw unprocessed image and tracking that value.

Everything seemed to come out ok, although I have no feel for what an acceptable range would be. Something I’ll have to work out I suppose. In the meantime, this lack of any kind of exposure index seems like a potentially serious issue as far as providing feedback to the technologist.

The other new thing that needs to be done is the detector evaluation. These detectors need to be properly calibrated, and I’ll probably have to include procedures for verifying the calibration. Somewhere in the world of AAPM subcomittees and task groups, there was one putting out a report on testing CR and DR units, which is something I’ve been waiting a while for and is just what I need for this task. I didn’t see it on the list of active task groups, and last I heard the final report was coming RSN, so hopefully I’ll see something soon.

We’ve got a couple more DR rooms being installed in the next few months (hopefully), so I’ll have a chance to try out some new procedures in a little while.

The last week or so has been pretty hectic trying to get everything ready for our new GE Discovery ST PET/CT scanner. Yesterday after a bit of unexpected downtime in the morning, we did the first two clinical patients which went smashingly well. Four more patients on the schedule for today. Lots of work for me to do still on the unit for acceptance testing. Probably should have gotten it done last week, but there were plenty of other things going on with the scanner to keep me busy. Looking foward to finally getting the NEMA PET tests started tomorrow and Friday. In the meantime, I get to go acceptance test my first DR unit tomorrow morning. Should be an interesting experience.

“We’ve had a misadministration”

As a diagnostic medical physicist, you don’t hear those words very often (unless you’re talking to a therapy physicist), nor do you want to hear them very often. Not because something really really bad has happened, but mostly because it involves a lot of paperwork and calculating and almost always happen when you’re in the middle of doing other things that need to be done yesterday.

Continue reading “Four words that are never good to hear”

Good: Today I got asked by one of our rad techs to speak at the SCSRT meeting coming up in about 6 weeks.
Inconvenient: I need to come up with a topic and outline by tomorrow so the organizers can send all the info in to get the meeting approved for CE credits.
Good: I can speak on whatever topic I want.
Bad: I don’t know what I want to talk about. Current ideas are digital detector technology and identifying image artifacts.
Bad: Whatever I end up talking about will mean lots of work preparing and researching.
Good: I can get Cat 1 CE credits for doing this.
Bad: It goes on the list with all the other things that need to get done in a very short time period.
Good: Something else to add to my CV.
Good: I can probably use this as a MOC SDEP
With my luck I’ll be the last speaker on the last day of the meeting.

Any nuclear medicine techs out there looking for a job in a well staffed reasonably state-of-the-art teaching hospital? We have an opening for a PET/CT technologist in our Nuclear Medicine department. Dual RT and NM certification is required.
Apply at https://www.applymuscjobs.com/. Click on Search postings and select Radiology Services in the Division dropdown to find the posting.