Reminders:

American Registry of Radiologic Technologists

A reminder to those of you who are licensed that as of this month, January, 2008, all CEU's acquired after the 1st of this month must be "category A" in order to count toward your license renewal. According to the ARRT, in order to be considered "category A," continuing education credits must be as follows:

* have been approved by a Recognized Continuing Education Evaluation Mechanism (RCEEM), and/or
* meet the definition of approved academic course, and/or
* be for certification in advanced-level CPR, and/or
* be earned through passing additional certification exams.

American Society of Radiologic Technologists

I would have liked to post this one sooner, but the ASRT deadline for scholarships is February 1, 2008. You can acquire scholarships for any discipline or even for extended education beyond your Associates Degree or Radiologic Technologist Registration by viewing the ASRT website.

Accuracy of ARRT Preliminary Test Scoring

I just received a comment on the "In the News" post asking about the accuracy of the preliminary results that the ARRT is going to be giving when graduates finish their Radiography Registry Examination. Since I only wish I had all the answers, I figured I would take my own private little survey of the students who read this blog. There is now a poll on the right-hand column of this blog for those of you who have received preliminary results to mark your results on.

I would not expect to see a variation much over 10% between the two, and here's why: If there are 20 pilot questions out of 200 that don't count toward your score, and they happen to factor those into the preliminary results that they give you on test day, that's 10%. There could be other variables as well that would make them more inaccurate. Since they're planning on adding new content to the Registry, I would expect there to be some inconsistencies at first with clarity and/or presentation of a new question or two. As an instructor myself, I know what answer I'm hoping the students will choose, but I have to write an appropriate question in order to lead the well-studied test taker to the right selection. But I am only one person, and the mighty ARRT has a huge panel of experts, test writers, many more years of experience writing tests, and the ability to implement pilot questions, so they might not even consider this an issue.

All in all, I'm excited to see what you all post on the poll. If there's a wider margin than 10%, feel free to post a comment or email me and I can add a new category to vote on within the poll. Just in case you don't know how to calculate percentages, you can... wait, your Radiography graduates, you know how to do that! :-)

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To Grid or not to Grid...

...that is the question. We all learned (or are in the process of learning) in school to use a grid on anatomy over 10 cm in part thickness or on techniques that require more than 70 kVp. But when you get right down to it, most technologists are not using grids for their portable chest x-rays. Why could this be? I'm so glad you asked... most grids have the lead strips running along the long axis of the grid. If you practice angulation perpendicular to the sternum (see prior "Lordotic Much" post), then you will find yourself with tons of grid cutoff when performing a crosswise cassette/grid placement. Having tried this on Kodak and Fuji systems with a lengthwise cassette, I can honestly say that the images are quite better. I'll give you one guess which of the following images was taken non-grid vs. with an 8:1 grid:



I know what you're thinking... "so what do I do when I have a crosswise chest x-ray to perform?" Well, you're pretty much out of luck unless you can convince your radiology department to purchase a few SD (short dimension) grids. Some companies manufacture these, and as we all know, grids can be very expensive, so take extra special care of these. The grid lines are arranged along the short axis of the grid to allow for crosswise placement, and to give the technologist the ability to angle cephalic or caudal without having those unsightly grid lines on your finished radiograph.



On a special note to anybody planning on purchasing these grids, make sure to check two aspects of your CR equipment before purchasing them. First, you need to see how your cassettes are scanned by the image reader (the laser will most often scan the photostimulable phosphor plate perpendicular to the direction of travel). If the CR system scans along the short axis of the phosphor screen (the same axis as the SD grid), then you want to make sure that the grid frequency (not ratio) is slightly higher than the scan frequency. This will prevent an alaising/moire artifact shown here:



Be sure to check with your quality assurance team to ensure that you are purchasing the proper grids at the right grid frequency.

kV, mAs, and density

One of the more difficult topics for first year students is the correlation between kV and density. Once you think you have this concept down, including the 15% rule and the subsequent lab experiments, this topic gets revisited a number of times throughout the entire x-ray program, and some very good questions about kV, mAs, and density typically arise. For instance:

Does the number of photons increase as kV increases?

Well, yes... let me explain first by clarifying that the number of electrons produced at the cathode does not increase - that is controlled only by mA while the duration of production is controlled by the time.

Now, let's say I have a technique of 65 kV and 10 mAs for a knee x-ray. A certain number of electrons are converted to x-ray photons at the anode during that exposure, and then a certain number of primary photons are converted to secondary and tertiary photons and so forth when they interact with the patient until one of two things will happen to all photons:

1 - they will leave the patient as scatter or expose the film
2 - they will lose potential difference and become absorbed in the patient

Now let's focus on the photons in the latter category... when we increase kV, we know that more photons reach the film because they have increased energy to penetrate the patient, but something else happens. There will still be a percentage of photons that will be absorbed in the patient, but it will not be as high of a percentage as the 60 kV exposure. You will now, at 75 kV for instance, have more energy even in the photons that are absorbed, to ionize tissue before those photons deposit all energy into tissue.

To clarify, let's say we have a characteristic interaction between a primary x-ray photon and an atom of carbon in the patient. We'll also say that this photon carried 75 kV of potential difference. The binding energy of the k shell for carbon is .28 keV, so we're left with a secondary x-ray photon of 74.72 keV with the ability to produce the same reaction approximately 267 more times (75/.28) before it is absorbed and each reaction produces more photons that will be absorbed. If the same series of reactions occurred with the 65 kV exposure, then you would only have a possible 232 of these identical interactions before the photon's energy is absorbed.

Keep in mind that this is only one example of a photon's interaction with matter, and there is always that randomness applied to how they react. If you haven't studied compton, photoelectric, or characteristic interactions yet, don't feel bad if you didn't understand the last paragraph. Just remember that when a photon interacts with matter, other photons are typically produced, or electrons are ejected that can ionize adjacent atoms as well, and increasing kV will increase the number of interactions that occur before the photons are absorbed.

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Hmmmmm...

After quite some time of hardcore thinking, and having been a member of several radiography forums and reading in the blogs around the world dedicated to radiography, I am leaning toward the re-dedication of this blog to be geared more toward students and the topics that are underway in the midst of their prospective courses of study.

I think it may be beneficial to open discussion about some of the more abstract concepts that can sometimes be glazed over in the classroom that there might not have been time to thoroughly investigate during lecture. That being said, feel free to ask questions, submit topics or comments, offer input, and share experiences here.

Updates to Curriculum

In the next few years, the ARRT and ASRT will begin to employ some additional topics including more direct digital and CR equipment on the content specs and in the Registry examination. Efforts are being made in Radiography programs across the country to incorporate these changes to better prepare students for their boards after graduation. There are going to be some pilot questions regarding image acquisition, construction and function of the CR processor and photostimulable phosphor screen, and DR image receptor. Computer basics and networking basics may appear, as well as technical factor selection and a whole new slew of image artifacts with digital imaging.

Those of us who have never had an introduction to this material might benefit from continuing education courses offering these topics. For instance, studies are showing with CR and DR that scale of contrast is not primarily controlled by kVp anymore, as we are all used to with film/screen imaging systems, but it is mainly determined by the algorithm selected at your QC station (chest/hand/c-spine etc.), with kV having a wider range of usability, and becoming a secondary factor. The possibilities for lowering patient dose with administration of higher kVp and lower mAs is highly effective. This is only one of the many changes that come with updates to our imaging systems.

After attending a digital radiography seminar for educators at UNC in Chapel Hill, I can honestly say the changes to what we've studied and known in the past about radiography are extreme. I challenge everyone who is reading this to embrace those changes. In order to stay competent in our highly technological field, we must all strive to keep up with this technology, and to continually try to adhere by the standards of ALARA, keeping dose low with image quality high.