CPU transplant successful!

The Xeon W3690 transplant was a success!

Ads in WordPress email notifications

If you’ve subscribed to my blogs via email (all three of you), you might have noticed that ads suddenly appeared in the email notifications. The email notifications are handled by WordPress’ Jetpack plugin, and the ad injection is apparently a recent addition.

Despite the note that say “This post is ad-supported”, these ads weren’t inserted by me. I’m not a fan of the ads just suddenly appearing like they did and I really don’t like that it says “This post is ad-supported”, implying that I’m the one doing the ad injection and that my posts and blog are ad supported.

Except for the occasional referral link that might appear in a post here and there, none of my posts or blogs will ever be ad supported.

If the ads in the email notifications bother you, feel free to unsubscribe. You won’t hurt my feelings. In the meantime, I’ll see what happens and investigate other options for email subscriptions.

Update: Looks like while I was leaving a comment on the Github issue, the Jetpack devs undid the ad injection.

A Xeon CPU upgrade for the computer

I picked up a used Xeon W3690 CPU from eBay to upgrade the Core i7-930 currently powering my computer. Browsing around eBay, I found several for under $80. For two extra cores and a few hundred more MHz, it seemed like a pretty good deal to me so I picked one of them and bought it.

The existing CPU still works fine, but after seeing a few friends talking about computer upgrades, I did a bit of research to see what I could put into mine to give it a bit of a boost without having to do a complete computer replacement.

My choices were dictated by the motherboard revision (a Gigabyte GA-X58A-UD5 Rev 1.0) and BIOS version (F7e). The best CPUs supported by this combination were the Core i7-970 and the Xeon W3690.

Doing my quasi-semi-annual computer cleaning and replacing the CPU will be a good weekend project. With luck, this computer will be up and running with a “new” and faster brain.

How much scatter radiation exposure?

video created by instructors in the Radiologic Technology program at St. Johns River State College and shared over on the Radiology subreddit, reminds technologists to wear lead aprons when doing portable radiography. 

In the video, they use what appears to be a Geiger-Mueller (GM) survey meter to show that even when standing far away from the portable unit or behind a wall, technologists are exposed to scatter radiation that is greatly reduced when wearing a lead apron.

Conventional wisdom for portable radiography tells people to stand at least 6 feet away (about 180 cm) during exposures and that the amount of scatter radiation that far away is pretty low and insignificant.  Most portable units have the exposure switch on a pretty long stretchy cord, so getting 10 feet away (about 305 cm) isn’t that difficult.  However, due to room/area constraints, it might not be possible for other patients/staff to get that far away.

One could definitely argue about the appropriateness of using a GM survey meter to measure scatter radiation, but for demonstration purposes it’s a reasonable instrument to use.  To quantify how much scatter radiation technologists are exposed to, an ionization chamber is a much more appropriate instrument to use.  Prompted by the video and spurred on by my own curiosity, I decided to have a quick look at the amount of scatter radiation.  Armed with my Radcal meter and 10×6-1800 large volume ionization chamber, I did some quick and dirty measurements to investigate.

To simulate a maximal scatter situation, I used two 32 cm CTDI phantoms as my large “patient” and a 35×43 cm field.  Source-detector (SID) distance was set to 100 cm.  The center of the ionization chamber was positioned 225 cm away from the center of the field (the farthest away I could reasonably get in the room I was in) and 94 cm above the floor (approximately waist height for an average sized person).

Three exposures at each of 60, 80, 100, and 120 kV were acquired and averaged.  To ensure a decent amount of exposure at the chamber, 50 mAs was used for each exposure.  The table below gives the average scatter exposure recorded at the chamber in nGy/mAs and the scatter exposure normalized to a distance of 100 cm.

Portable Radiography Scatter Exposure
kVScatter exposure
(nGy/mAs)
Scatter exposure
(nGy/mAs) @ 1 m
6017.588.8
8043.2218.8
10079.5402.6
120123.9627.2

Plotted on a graph, it looks like this.

Portable Radiography Scatter Exposure
Portable Radiography Scatter Exposure at 225 cm

A second order polynomial fits the data pretty nicely: Scatter (nGy/mAs) = 0.0117kV2- 0.3279kV - 5.0002

Consider an abdominal radiograph performed at 80 kV and 40 mAs.  From the graph, scatter exposure is about 40 nGy/mAs.  At a distance of 225 cm, the scatter exposure would be about 1.6 μGy.  At a distance of 10 feet, inverse square correction (a reasonable approximation) puts the scatter exposure at around 0.87 μGy.  At a distance of 6 feet, it would be a little higher at around 2.4 μGy.

This data only represents one unit, one measurement location, and a maximal scatter setup, but still illustrates that while scatter is detectable, the exposure to surrounding people is still fairly low.

How applicable are these numbers generally?  For radiographic units (fixed and portable), it turns out that there’s not as much variation in radiation output as one might think.  The amount of scatter exposure will vary with location around the source (lower behind the portable unit because of shielding by the portable) but should be fairly symmetric.  It probably wouldn’t be too unreasonable to use the data here to get ballpark figures on how much scatter exposure technologists and other personnel would be exposed to.  Remember, the data presented here represents kind of a worst case scenario with a large patient and large field, so any estimates based on these numbers should be considered as upper limits.

If you’re a technologist who does a lot of portable radiographs, wearing a lead apron and keeping your distance probably isn’t a bad idea.