A new portable x-ray unit

A new Carestream DRX Revolution Nano portable x-ray unit arrived at work this week. Normally the arrival of a new portable x-ray unit wouldn’t be a terribly notable event, but the size of the unit and label on the tube head intrigued me.

It’s a pretty compact unit (about the size of a shopping cart), weighing in at just over 100 kg. The x-ray tube is considerably smaller than a normal x-ray tube. I was told by the service engineer that the x-ray tube uses carbon nanotubes for the cathode. I had read about this technology a few years ago, but wasn’t aware that it was being used commercially. This is the first application I’ve heard of in the medical imaging world.

The machine is quiet during the exposures, without the normal sound of an x-ray tube anode spinning up, so I suspect this is a tube with a stationary anode.

The Nano turns out to be a pretty low power unit, even for a portable unit. The x-ray technique maxes out at 110 kV and 12.5 mAs. At 60 and 80 kV, the maximum mAs was 20 and 16 respectively. Not entirely sure if this was just a soft limit based on the imaging protocol I selected, or a hard limit. I still need to go through the documentation and the technical specifications for the unit.

Radiation output in mGy/mAs was pretty similar to a conventional x-ray tube (compared to a Shimadzu portable unit in the graph below).

Radiation output (mGy/mAs) graph
Radiation output for the Carestream Nano (orange diamond) and Shimadzu portable ( blue square)

Exposure times for the Nano were quite a bit longer though, so the tube obviously operates at a considerably lower tube current than a conventional x-ray tube. Pretty clear from the exposure rate graph below that while the mGy/mAs is similar, the Nano tube is spitting out much less radiation.

Exposure rate (mGy/s) graph
Exposure rate (mGy/s) for the Carestream Nano (orange diamond) and the Shimadzu portable (blue square). Multiple values at 80 kV are exposures at different mAs settings.

Crunching a few numbers, I found that the tube current for the Nano goes between 30 – 60 mA, about 1/4 of what I might expect for a regular portable x-ray unit, but about what I’d expect for something with a stationary anode.

kV/mA graph
mA range at different kV settings for the Nano (orange diamond) and Shimadzu portable (blue square)

As far as the kV and exposure rate wave form goes, it’s about as perfect as I’ve ever seen from any x-ray tube. Excuse the small size of the graph. The software for my meter started spitting out tiny images into my spreadsheets instead of the big ones it used to, and I haven’t figured out how to fix it yet.

kV and exposure rate wave forms for the Nano
Exposure rate (green) and kV (red) wave forms from the Nano

It’s a pretty neat little unit. Should be pretty decent for imaging babies and small kids (unless they’re very squirmy), but probably a bit under powered for imaging anything larger than a toddler. I predict the addition of at another more conventional portable x-ray unit a few months down the road.

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