The two wikis I set up for other groups to manage their documentation have now expanded to four (including my Medical Physics wiki). At about 45 MB for just the code, I realized having multiple Mediawiki installs running around was quickly going to suck up a lot of disk space and be a PITA to manage, especially for upgrades.
After trying it out on my test server, I now have all four wikis running off the same installation (took about 20 minutes). One copy is much easier to maintain than 4 separate ones, although one significant flaw in Rumberg’s approach is that if future versions introduce new files, some of them (depending on where they’re located) will have to be manually linked into the other wiki’s. Still much better than having to manage multiple installations.
Now what I need to do is set them up with a common help that’s sufficiently customized for the local installation.
Physics Corner was a series of articles I wrote for an incarnation of the department newsletter between 2000 – 2001. They’re collected here for posterity and maybe to provoke me into starting it up again as an online column.
A common attitude in diagnostic radiology is that most procedures are relatively safe and carry very little risk of causing further harm to patients. For the most part, this is true. However, some may be surprised to learn that in recent history, there have been several documented cases of radiation induced skin injury to patients resulting from prolonged fluoroscopic procedures. In fact, an advisory was issued by the FDA in 1994 warning of the potential for radiation injury resulting from prolonged fluoroscopic procedures such as PCTA, stent placements, ERCP, cath lab procedures and RF ablations. The text of the advisory is available online at http://www.fda.gov/cdrh/fluor.html for those interested in reading it.
The first effect of excessive radiation exposure to the skin is erythema (skin reddening). Erythema, which has a threshold of 200-600 rad (2-6 Gy), looks just like a sunburn and often has the same shape as the x-ray beam (circular or square). For an average sized patient, the skin entrance exposure rate to the patient can vary between 4-7 R/min (35-60 mGy/min), depending on the projection angle, size of the patient and type of tissue in the field. At these typical exposure rates, the threshold for skin erythema can be reached with less than an hour of fluoro time. For cine runs, patient exposure is even higher, around 50-100 R/min (440-875 mGy/min), and the skin erythema threshold can be reached with a few minutes of cine.
In the majority of fluoroscopic studies performed, the radiation exposure to the patient is well below the threshold for inducing skin erythema. However, even with today’s technology, the potential exists for radiation induced skin damage to a patient, and it is this potential that every fluoroscopist should be aware of when performing a procedure on a patient.
coronary angiography followed by coronary angioplasty
skin lesion
101 minutes, 78 cinefluorography runs, 18 Gy
Female, 25, USA
RF cardiac catheter ablation
skin breakdown 3 weeks post procedure
unknown, procedure time of 325 minutes
Female, 62, USA
balloon dilation of bile duct anastomosis
burn-like back injury on back requiring skin graft
unknown
Female, 61, USA
renal angioplasty
skin necrosis requiring skin graft
unknown, procedure time of 165 minutes
A very interesting case study can be found at http://www.fda.gov/cdrh/rsnaii.html discussing one particular incident of radiation injury from a coronary angioplasty procedure.
There are several methods that operators can use to minimize the radiation exposure to themselves and the patient:
Keep the total fluoro time for the procedure as low as practical. Most fluoro systems in this institution come with a last image hold. Learn to us it.
Keep the II as close to the patient as possible and the x-ray tube as far away as practical. As the II is moved away from the patient, the system increases the fluoro technique to maintain image quality. Keeping the x-ray tube far away from the patient reduces the patient’s exposure via the inverse square law.
One of my ongoing projects at work has been to document the test procedures and processes we use. I initially started with putting them into a CMS (e107) but recently decided to switch to a wiki format. Inspired by CharlestonWiki and after using Mediawiki for a couple other wiki documentation projects in the department, I’ve started up my own medical physics wiki project.
For the most part, It’s going to contain all the test procedures and work processes specific to the way we do medical physics here in MUSC Radiology, but I plan to include a lot of other general diagnostic medical physics stuff as well. It’ll be a place for me to dump all the stuff I know about diagnostic medical physics and imaging. It’s going to primarily be for personal reference, but if other people benefit from it, so much the better.
Physics Corner was a series of articles I wrote for an incarnation of the department newsletter between 2000 – 2001. They’re collected here for posterity and maybe to provoke me into starting it up again as an online column.
When it comes to measuring and counting radiation, there are more ways to measure radiation than you can count on your fingers. And to top it all off, there are the traditional Imperial units, and the more modern SI units to confuse things even more. In this month’s column, I’ll attempt to demystify the world of radiation units.
When you boil it all down, there are essentially two types of units used for quantifying radiation. There are physical quantities used to measure the amount of radiation or energy deposited, such as the roentgen or curie (for radioactive materials), and there are units to measure the biological effect of radiation (such as the rem). The table below summarizes the different types of units used.
Ionizing radiation produces charge pairs (electron and ionized atom) when it interacts in matter, so naturally this is the first thing we look at. Plus, it’s also very easy to measure. The roentgen represents the amount of charge produced per unit mass of air and is the unit most commonly seen. In SI units, the unit of exposure is simply coulombs/kg (C/kg), which is sometimes referred to as X. The roentgen or C/kg represents a considerable amount of radiation. Exposures in the diagnostic radiology realm are generally measured in milli-roentgens (mR), or 1/1000th of a roentgen. For a little bit of perspective, the exposure to a patient receiving a chest X-ray at MUSC is typically 10-12 mR.
While knowing the exposure can be useful (in a “more is usually bad” kind of context), it doesn’t really mean much when it comes to predicting biological effects of radiation exposure which is generally what most people are interested in. In order to assess biological effects of radiation, first we need to know how much energy is deposited in matter. This is generally referred to as the absorbed dose. In the old system, the unit for absorbed dose is the rad (radiation absorbed dose), while the gray (Gy) is used in the SI system. Both units measure the amount of energy in joules (J) deposited by radiation in a unit mass of material (J/kg). For most diagnostic x-ray procedures, the absorbed dose is generally measured in the milli-gray or milli-rad region.
When it comes to radiation risk and protection, a couple more units were introduced because different types of radiation have different effects. In the old system, the unit is the rem (radiation equivalent man) and the sievert (Sv) in the SI system. As with the rad and the gray, 1 Sv = 100 rem. Both the rem and sievert unfortunately have units of energy per unit mass, just like the rad and gray. However, the rem and sievert are related to the rad and gray by a numerical scaling factor known as RBE (relative biological effectiveness). RBE relates the effect of a particular type and amount of radiation to a reference amount of x-ray radiation. X-rays and gamma rays are assigned an RBE of 1, while alpha particles are given an RBE of 20. So, while an exposure of alpha particles might deposit say 1 rad of energy within an organ, the actual effect on the organ would be the same as that produced by 20 times as much x-ray radiation.
All of this might look and sound rather messy but in the world of diagnostic radiology where the conversion factor from roentgens to rads is close to 1 and x-rays have an RBE of 1, things are a little simpler: 1 R ~ 1 rad = 1 rem.
For radioactive materials, the amounts of radioactivity present are measured in curies (Ci, old unit) or becquerels (Bq, SI unit). Traditionally, the curie was defined as the amount of radioactivity contained in 1 gram of radium-222. Now, the curie is defined as 3.7×1010 disintegrations per second. The becquerel is defined to be 1 disintegration/sec, so that 1 Ci = 3.7×1010 Bq. The curie represents a tremendous amount of radioactivity, and is definitely not something to be carrying around in your front pocket. In nuclear medicine departments, the amounts of radioactivity used are generally measured in milli-curies (mCi) or micro-curies (μCi) (mega-becquerels (MBq) and kilo-becquerels (kBq) respectively).
Physics lectures for the first year radiology residents are starting up again. I’d forgotten I was going to be giving one of them tomorrow, so most of today has been spent reviewing the lecture and making a few minor tweaks.