Today I get to mess around with our newest cath lab acquisition. Actually I did some initial messing with it doing the acceptance testing earlier this month, but now I get to play and have some geeky medical physicist fun with it.
It’s a fairly unique (for the US) system and very cutting edge. As far as I’ve been told, it’s the first system to be installed in the US. A Siemens Axiom Artis with a couple of really large magnets from Stereotaxis used for steering a sepcially designed catheter guide wire through the arteries of the heart.
The x-ray system itself is the first flat panel fluoroscopy unit I’ve laid my hands on for testing. These things are impressively small and compact. Image quality and performance was ok, but not stunning. Noticed some pixellation getting to the smaller mag modes, but nothing severe.
HTTP SEARCH Protocol attacks
Yesterday my server got hit by about 15 attempts to find what I guess to be some kind of buffer overflow vulnerability in my webserver using some kind of HTTP SEARCH method. Never knew there was such a method until now. At first, about the only verifiable reference I could find about it was an old W3C page indicating it was only a proposed method. No mention of it in the HTTP RFC 2616 document at all. Then I found (thanks to Google) a reference in someone’s presentation on DAV properties starting here. Seems to be a DAV thing. I only found mention the SEARCH method in a draft document.
The client invokes the SEARCH method to initiate a server-side search. The body of the request defines the query. The server MUST emit an entity matching the [RFC2518] PROPFIND response.
The SEARCH method plays the role of transport mechanism for the query and the result set. It does not define the semantics of the query. The type of the query defines the semantics.
Of course now that I know it’s a DAV thing, there’s plenty of stuff out there about it.
Basically the attack consisted of sending a really long SEARCH request (similar to sending a HEAD/GET/POST request I suppose) containing well over 8K worth of \x90, \xb1, \x02 and probably followed by other things. Apache 2 logs it as “request failed: URI too long (longer than 8190)”. I take that as a good sign Apache 2 isn’t vulnerable to this kind of attack.
All of the requests came from very different IP addresses which points to some kind of DDoS type of attack.
Always a good idea to keep an eye on the log files. They can tell you a lot about what’s going on with your system. One of these days I’ll have to make like every other decent sysadmin type out there and set up some scripts that scan the log files and mail me the interesting bits.
Journal Club: Impact of increased Al filtration on X-ray tube loading and image quality in diagnostic radiology
One of the main reasons to read papers is to learn things. Preferably new things. This is one of those papers where you can pick up a few ideas for analyzing or looking at data or measuring something that you may not have initially thought of. This was certainly the case for me while I read this paper.
There are two effects of additional filtration: reduced patient entrance exposure (from removal of low-energy x-rays) and increased tube loading (from increased technique to compensate for the radiation removed by the additional filtration).
The change in mAs for varying amounts of added filtration and different projections was examined under three conditions: constant patient entrance exposure, constant patient exit exposure and constant film optical density. If I was doing the same study, I probably only would have thought to look at entrance exposure (since it is easiest to measure) or CR exposure index (we use digital systems here).
Maintaining constant entrance exposure required the highest increase in mAs for a given amount of filtration, while maintaining constant film density required the lowest increase. To avoid increasing the amount of image noise with added filtration, I think the ideal parameter to maintain would be constant optical density (or receptor exposure for digital systems). Since maintaining constant optical density is more labour intensive to measure, constant exit exposure is probably an easier parameter to work with (and already measured by phototimer systems). Both methods resulted in similar increases in mAs.
Increased technique also affects image quality due to focal spot blooming when the tube current is increased. However this is normally a very small effect, which was confirmed by the authors. There is also the potential for increased motion blur when exposure time must be increased, but with the constant exit exposure/optical density methods, the increase in exposure time was small enough so that motion was not a problem.
Even with 4.0 mm added filtration, the increase in mAs should be well within the range of x-ray units to accomodate by increasing mA and/or time without adversely affecting image quality.
Overall I thought this was a well done paper that clearly showed that the impact of added filtration was minimal and easily accomodated by most x-ray systems.
POPfile does SQL
POPFile 0.21.1 got released a little while ago, and I noticed it supports storing it’s word corpus in an SQL database. So I decided to try it out and upgraded a few days ago. A relatively painless procedure documented here.
Just had to install Perl on my Win2K box (ActivePerl from ActiveState) and install a couple of modules.
POPFile with the MySQL backend runs a slower than it did using the flatfile BerkeleyDB. My machine running MySQL isn’t the fastest in the world, so I blame it. I imagine it would be significantly faster with the DB server running locally.
Having the corpus and word matrix stored in an SQL database makes it easy to see what’s going on. You can see what words have been classified, what buckets they belong to and how many times they occur. Makes it easier to dig out some statistics (if you want to do such things) about POPFiles word classification.
There are a few other changes to POPFile that make the 0.21.1 upgrade worthwhile. Switching to a MySQL backend from the default involves a little more work, and if you don’t care about it, stick with the default.
If spam is a problem for you, and you want something simple to help manage it, I definitely recommend POPFile. Since the upgrade, POPFile’s gone through 3000+ messages with only 24 misclassifications so far.
Now if only I could get my Groupwise mail to go through POPFile also…
ick, it looks like crap
Hmm, just noticed that my weblog looks like crap under Netscape 7. It’s mostly ok in IE 6. Looks just fine in Mozilla/Firefox. I must have style sheet and DIV issues. Wish someone would tell me these things.