Category: Work stuff

One of the things I’ve been working on lately is collect images to fill out my image artifact gallery. Today while acceptance testing a new C-arm, I had a chance to demonstrate what happens when large hunks of metal get moved past or near the image intensifier.
All conventional vacuum bottle based image intensifiers are prone to distortions caused by magnetic fields or changes in the ambient magnetic field (which is what large metal objects do), changing the path of the electrons as they travel from the input photocathode to the output window. Normally, image intensifiers are shielded from any stray magnetic fields by mu-metal. It usually works pretty well, but mu-metal can only do so much. IIs will still be prone to distortion when large enough hunks of metal get moved by.
Below is an image of a linear grid phantom (click on the images to see a larger version in the teaching file gallery). All the lines should be pretty straight and perpendicular.

Below is the same phantom, but now a small stretcher has been placed next to the image intensifier. If you look carefully, you will see that now the lines look slightly S-shaped.

Here a much larger stretcher with more metal in it has been placed next to the II. Now the lines are much more distorted and more S-shaped.

If the large metal object is moved past the II during fluoroscopy, you see this cool twisting distortion effect going on as the object gets closer, and then returning back to normal as the object moves away. If you’ve ever been working on a CRT monitor when a large metal object moves by fairly closely, you will notice a similar phenomenon.

It’s been a good year at work. I’ve managed to get the department to purchase almost all the things I put on my wishlist this year, and now my office is almost overflowing with toys and equipment waiting for me to find time to play with.
The latest delivery was a much anticipated RTI Barracuda survey meter. This is something I’ve had on my wishlist for a long time. It comes about as close to a ‘do it all’ device for us diagnostic physicists as anything else out there. The real reason that I really wanted one this year is because of this: the CT Slice Detector. It’s a 30 cm long chamber that’s supposed to provide dose information at each point along the length of the chamber. Instant dose profile information. Whoops, spoke too hastily without really knowing how the chamber worked. So it’s not exactly what I thought it was, but still gives the same information. After a little more reading about the CT-SD16, I discovered it’s actually 1 long chamber with two separate solid state detectors separated by 16 cm. Dose profile information is obtained by doing a regular helical scan with the chamber in the phantom so that the detectors are advanced through the beam. Seeing as how I have the annual surveys for our CT scanners scheduled for the next few Friday’s, the Barracuda came just in time too. I’m so looking forward to playing with this new CT chamber. Especially can’t wait to try it out on our flat panel CT scanner. Dose profile on the flat panel CT isn’t going to be as easy as I hoped, but I’ll figure out something to make it work.

This year’s pumpkins were on display today. Not as many as last year, but there were a few pretty good ones. This year’s 1st place winner was the Blood Bank. Surgery’s pumpkin was kinda cute.

It’s not often I get a chance to write a paper for submission to a journal or meeting. But when I do, I always seem to be torn between choosing to write it using plain old MS Word, or going with TeX/LaTeX. I’ve always liked look of TeX generated documents. Problem is I’ve learned enough TeX/LaTeX to be able to generate some simple equations, but still haven’t learned enough to make a full fledged document. A couple of TeX books sit on my shelf to help me learn more (one of them seems to be missing…), but it’s always a slow process, because some of the things I end up wanting to do always seem to be things that have a hard time finding solutions to.
And then it comes to crunch time, and usually I end up falling back to MS Word, because it’s quick and easy. Just doesn’t look quite as nice or sophisticated though.
This time, though, I’m determined to do it in TeX. I have a working TeX environment in the form of MikTeX and what appears to be a decent TeX editor in TeXnicCenter (used Emacs before).
Time to go get started…

The latest addition to my collection of phantoms, the Hoffman 3D Brain Phantom from Data Spectrum showed up at my desk yesterday. It’s got some refinements compared to an earlier version I worked with several years ago that make it easier to reassemble if it gets taken apart.
It’s a pretty cool phantom made up of a bunch of different plates with patterns cut out to simulate radionuclide uptake in the brain. Looking forward to doing a few projects with this one (that list just keeps getting longer and longer).