#9       How Much Off-Focus Radiation Comes Out of the Tube?                         5 /1/13

     Today's blog is about off-focus (stem) radiation which until a couple of weeks ago I had completely forgotten about.  As a reminder to all of you who haven't cracked open your physics books in a while; off-focus radiation are x-rays produced by stray electrons that interact at positions on the anode at points other than the focal spot and are emitted at angles not in the primary beam.   This turns out to be a truly amazing subject when it comes to patient safety and shielding.  So much so that I have also put it in my website as the newest Current Research so you could see the photos, images and doses. 

     Last month my student Ian asked me if one should shield a patient having a PA chest in the front or the back.  I told him we had that same discussion in my class 37 years ago and that I still had no idea what was the correct answer.  We had figured that shielding in the back really didn't do much as most of the scatter occurred once the radiation hit the body or happened inside the patient.  Shielding in the front seemed like it might be more beneficial because maybe there was a certain amount of the exit beam that hit the Bucky and bounced off back at the patient.                                                                                                                             

     I decided to test this out using an 8x10 CR cassette that I would run at 1200 speed, making it extremely sensitive to any radiation.  In an upcoming Current Research I will show you exactly what we discovered when we put this age old question of front or back shielding to the test.  One thing that was extremely obvious right off the bat was how much radiation hit the cassette when placed on the back side (facing the tube).  I had hung the cassette lengthwise with paper clips taped on and every clip showed up on the image.  What made this so incredible was that none of the cassette was in the primary beam.

     So where was all this radiation coming from?  We thought it might be radiation that had scattered from the molecules in the air, but that seemed unbelievable.  After speaking with my colleague Quinn Carroll (who recently wrote the physics book "Radiography in the Digital Age") he told that this kind of scatter would be physically impossible.  We then thought it might be leakage radiation coming through the collimators.  After showing my research to an amazing group of physicists I am in contact with, they determined that it is off-focus radiation.

     I now changed the experiment to have as few variables in it as possible.  I wanted to use my dosimeter so that I could have exact readings as to how much dose was being emitted that was not in the primary beam and I already had ideas on writing this up for a peer reviewed article for the ASRT Journal.   I used a large conference room and our AMX portable machine so that I could hang my ion chamber with nothing remotely near it to cause back or side scatter.  I then made close to 400 exposures (for a peer reviewed experiment all "projections" need to be done 5 times and then the average is taken from that).

     I collimated the beam to 14x17 at a 72"SID with the bottom of the light field just above the ion chamber.  I used 2 average chest x-ray techniques: 85 kV @ 3.2 mAs and 115 kV @ 4 mAs.  Then I moved the tube 1" higher and made those 10 exposures again and continued an inch at a time.  With the 85 kV technique I needed to go 14" higher before the readouts were not accurate anymore.  With the 115 kV technique I was still getting precise readouts at 28" above the ion chamber but the tube could not go any higher.  I also did the experiment at a 40" SID using 85 kV @ 16 mAs to show how this would all pan out for an average abdomen technique.

     What has been proven so far is there is definite radiation below the collimated light field, more so on bigger techniques.  Although the dose is in the MicroR's (1/1000ths of a milliroentgen) one needs to be aware that there is a noticeable dose hitting the body outside of the primary beam.  My hospital has a 100% shielding policy, but if yours doesn't then you should definitely be aware of how much extra radiation is getting to your patient.

Please go to the Current Research to see what all this looks like.   

    

Link to Digital RadiographySolutions website 

# 8       Universal CR & DR Technique Charts        4/15/13

     Back in the film days I would always give my students a technique chart that had about 50 different body parts on it.  When we went digital in 2002, our vendor told to use the same techniques, so we continued to use those charts.  Four years later we had learned all about the new optimum kVs from Barry Burns (for more information on optimum kV or why you would want to use a higher kV and lower mAs see blog #7 from April 1^st). 

     In addition, Barry had taught us that all the manufacturers used the same style of x-ray tube and all large facilities used the same high frequency generators.  Most important was the fact that regardless of what the manufacturers called their Exposure Index (EI) number, they all got their perfect EI number if the image receptor received 1 mR (for more on EI numbers and their ranges see blog #2 from January 15^th). 

     Because of this I had the idea that a universal technique chart could be created, but needed to talk it over with Barry first.  He agreed that as long as the x-ray room had a modern high frequency generator (all hospitals and large facilities have used only these generators for the past 25 years) then a universal chart was absolutely feasible.  So I took my film/screentechnique chart, had my student Callie DeGuzman sit at the computer with a blank Excel chart in front of her and I did the 15% and 7 ½% Rule changes to the old techniques and came up with the new ones using the higher kV and lower mAs.  Then we did this over 190 times and when we were finished we had a fully functional CR Universal technique chart. 

     Soon after our radiologist’s let us cut the mAs in half for every exposure (except for abdomen’s which had too much mottle/noise).  These new images had a tiny bit of noise, which our radiologist’s called “acceptable mottle”.  When you go my website and go into All Charts, you will see many versions of the CR technique charts.  The first one is titled “Least mAs”, and the next one is “33% More mAs", then "66% More mAs" and finally "100% More mAs".  What this means is there are 4 sets of charts which will work for all manufacturers except Konica, which has its own set of 4.  The first chart titled "Least mAs" has the lowest amount of mAs, or in other words, the lowest dose.  It would also have the biggest possibility of having images with mottle/noise.

     So what I suggest to everyone is to do the following: Start with the "100% More mAs" chart and see how it works in your department.  If the images are coming up fine and the EI number shows that you can use even less mAs, go to the "66% More mAs" chart.  If the EI number shows you can continue to drop the mAs, go to the "33% More mAs" chart.  Lastly you might be able to drop the mAs/Dose all the way down and begin using the "Least mAs" charts.  As I mention in the disclaimer, your radiologist should always the final word if your image is diagnostic. 

     A few years later two DR rooms were built into our new emergency department with third generation GE using Cesium based detectors.  Immediately we noticed that the techniques were noticeably less than our CR techniques.  Two years after that we had three Siemens DR rooms installed in our main department and from there I could now compare techniques between these two major manufacturers.  The Siemens Rad room has two built in Cesium based detectors while the fluoro rooms use a tethered Canon detector (Gadolinium based).  During this time I discovered how similar both the GE and Siemens techniques were.  It took a full 6 months of studying, writing and comparing techniques before I was able to develop the Universal Cesium and Gadolinium DR technique charts.  These charts are pretty self explanatory, other than you need to know if your detectors are Cesium or Gadolinium based.  The Gadolinium detectors use just about 50% more mAs than the Cesium detectors.

#7                 Optimum kV for DR & CR Equipment                 4/1/13

     As soon as the film-screen combination was developed in our profession, there has been optimum kVs used for every body part.  Even when Rare Earth screens came on the market in the early 80’s and the mAs was cut to one third (from 9 to 3 for example) the kV stayed exactly the same.  This is because these kVs were perfect for the density and molecular make up of that body part.  This is also why we use the same120 kV on a chest x-ray for a 100 or 300 lb. patient.

     The beauty of knowing, and using, the optimum kV is you are always using the perfect kV.  By using the optimum (or in other words the best) kV, it also means that any technique problem you will ever encounter is mAs related, not kV.  This concept holds just as true today with digital radiography as it did with film except for 1 huge difference.  The optimum kVs are now higher with most of the body parts.

     Back in the early days of CR Barry Burns, an adjunct Professor of Radiologic Science, University of North Carolina School of Medicine in Chapel Hill, now retired, who was also a radiographer and physicist, immediately realized that the optimum kV for film was not the same as CR.  After careful research and experimentation, he discovered that when using CR everyone can increase 15-20 kV from film/screen techniques (except Konica which is 5-10 kV).  When both Gadolinium and Cesium based DR detectors were introduced, it was discovered that they too could use kVs 15-20 higher than those used with film/screen.

     To see these “new” optimum kVs, please go to All Charts on the Homepage and view chart 1 and 2 (Konica).  You will discover that with the exception of chest, barium work and pediatrics, all other body parts have a very noticeable increase in kV.

     Why would you want to increase the kV in the first place?  This would be so you could decrease the mAs.  By increasing the kV 15% and cutting the mAs in half (what most people call the 15% Rule), the entrance dose to the patient is decreased by 33%.  This is such a simple way to cut one third of the dose to your patient.

     As always, it boils down to patient dose.  How high a kV and how low a mAs can you use and still have a perfectly diagnostic image?  That’s the question we all need to be asking ourselves before every exposure. 

     In the upcoming months I will have at least two more articles related to this subject.  They will be “CR & DR Universal Technique Charts”, which is pretty self explanatory and “How Low Can You Go?” which will discuss how low can you take the mAs (dose) and still get that perfectly diagnostic image.

Link to Digital Radiography Solutions website 

Blog #6                                                                       3/15/2013             How much can you over-radiate and still get a perfect image?                                                                                                                                                                                                                                 

I decided to write and post this blog on the same day I changed my current research on my website.  This subject is one of the most exciting and scary things that is happening in our profession at this time.   If you go to the Current Research section, you’ll see handfuls of images proving that 5, 10, 50+ times too much mAs can be used and the images all look the same.

When I first started going to lectures on digital radiography, I heard that using 3-4 times too much mAs would cause noticeable changes in the images contrast and resolution.  This didn’t seem to match what I was seeing with our CR and DR equipment, so after a year of pleading and begging, CHOMP bought four phantoms and digital dosimeter to go with our abdomen phantom.  And with that; the “game” to finally understand what we were doing was on in earnest.

The first blog I wrote was about Creeping mAs/Dose.  I explained that one the reason’s this is occurring is because the digital computers all have the remarkable ability to automatically rescale the image.   So now an unbelievable amount of mAs (meaning way too much) can be used and a prefect image is created almost every time.

Without a body phantom to experiment with, it is impossible to see how easy it is to over-radiate a patient and still have a perfect (or at least very passable) image.  I have now been able to use my skull phantom on nine different manufacturers to determine how much mAs can be used, and over-used.  Currently I have four CR and five DR vendors.

From the experiments I’ve performed, all of the CR manufacturers except Agfa have the ability to “fix” an exposure that has been over-radiated by more than 50 times.  That is automatic rescaling at its finest.  It is also why no human being can see if an image was only over-radiated 2 or 3 times too much.  This is why it is impossible for anyone to be able to look at a monitor and tell if the patient was over-radiated, unless enough radiation was used to create burn on the image.  This is also why the EI numbers are the only way a radiographer can tell if the technique was correct.

I could go on and on (and do when I get to this section of my lectures) but I just hope you have a few minutes to go to the Current Research section of my website and see the images for yourself.  If there ever was a time where a picture is worth a thousand words, it will be there.

Link to:  Current Research

#5    Grid Cut-Off in the Digital World     03 /01 /2013

 

     After years of wondering about it, sometimes noticing it and finally researching it, I’ve come to the conclusion that grid cut-off isn’t mentioned anymore because no one even knows it’s happening.  With film it was totally obvious because grid lines covered 50-100% of the image.  That is not the case at all with digital images.  This is because the post processing has grid suppression software built in that does just that – it suppresses the grid lines so they don’t appear in the image.

     This is a little good and a lot bad.  Good because the image doesn’t have annoying grid lines in it which could superimpose anatomy or pathology.  Bad because the radiographer does not know that there is grid cut-off occurring, with all the ill effects that grid cut-off creates.  These include:  decreased contrast, increased brightness, increased Exposure Index (EI) number, more technique (mAs) needed and possible decreased sharpness of detail.

     Whenever you are using a grid and the image has any problem with contrast, brightness, detail or EI number, it is almost a given that you have grid cut-off.  It is happening all the time and almost no one knows it.  In fact, most of the grids that come with both CR and DR equipment are incorrect for use with chest x-rays.

     There are many different styles of grids, but the 2 most common are with the grid lines running parallel with the floor (called a horizontal grid) and 90 degrees to the floor (called a “decubitus” or “short axis” grid).  When using the grid for any AP chest work where the central ray (CR) is being angled caudally into the patient and grid, the grid needs to be short axis so that the grid lines are still parallel with the CR.

     I did some experiments recently with the grids that came with both our GE and Siemens DR equipment and both of them were horizontal grids.  This isn’t written anywhere on them, but I proved it by taking chest phantom shots with a 10 degree caudal tube angle and the grid both lengthwise and crosswise.  With the GE grid it needed to be put in behind the patient with the handle to the side which is very difficult and the Siemens grid needed to be put in portrait and not landscape.  With our CR grids we had to purchase separate grids that were short axis so that we could continue to put the grid behind the patient crosswise.

     When you get grid cut-off, it means you have used more mAs than needed to get a proper EI number.  From my research I’ve concluded it’s around 30%.

     I was thinking I could have you go to the Presentation Download on my home page and look at the slides that discuss grid cut-off, but I do not have time to cover it in my 2 hour lecture.  It is only in my 6 and 8 hour presentations.  Sorry about that.  Hopefully one day I will have it on my site in the Current Research section. 

      

Link to: digitalradiographysolutions.com

#4    The Trouble with Post Processing “Collimation”    2-15-2013

     Post processing “collimation”, shuttering or cropping seemed to be one of the greatest features of digital radiography.  With our first CR unit we were taking badly collimated chest x-rays and then with a couple of mouse and key strokes turning in images that looked like we were the best collimating super techs in the world!! 

     After almost two years of this one of our radiologist’s finally realized something weird was gong on and asked what we were doing.  When we told and showed him, he couldn’t believe it.  He immediately told us that what were doing was basically illegal as the radiologist is legally responsible for every bit of anatomy that was radiated and appeared on the image receptor (IR).  This rule has not changed one bit since the film days.

     The predicament we have with this is no one even knows it’s a problem.  I know for a fact that in one somewhat large U.S. city two different hospitals were sued because the radiographer cropped out anatomy that was later proven to have shown a tumor.

     Picture this:  You take a lateral C-spine and get almost the entire mandible on the image.  You don’t notice that there is a small tumor in the mandibular body so you crop out almost the entire mandible, leaving just a perfect looking lateral C-spine.  Six months later lawyers looking through every image taken on their client sees that your images would have shown the tumor half a year ago.  Six weeks ago the patient had to have a huge part of their mandible excised in surgery because of the fast growing cancer.  Your hospital is now being sued for five or ten million dollars and they are not even going to try to fight it because it would be impossible to win.  It was completely your fault and everyone knows it.

     Now I know you haven’t heard about these two cases. Also if it’s happened twice in this city, what are the odds it hasn’t happened countless times in cities all over the country?  The reason this is still a secret is because the hospital is willing to hand over this incredibly large sum of money with one stipulation, and that is a gag order is invoked whereby no one is allowed to talk about the case.  So until the day a patient decides to have their day in court, we are not going to read or hear about this.

     So there are only two ways you can post “collimate” and have it still be legal.  First is to only crop out areas that are outside the border of the body tissue (white or black areas).  Second is to make a copy of the original image and turn it in along with the cropped version.

Back to digitalradiographysolutions website

#3                                How to Properly Critique a Digital Image                                  2-1-2013                             

          We have had hundreds of digital equipment training hours at my hospital in the past 10 years, but in all of that I don’t remember any time given in learning how to correctly critique the image.  I have to imagine this is the same with everyone around the country, possibly the world.

          Last month I wrote about how reliable the Exposure Index (EI) numbers are, especially when the collimation and centering were good.  Today I am again to reiterate that these numbers have to be a huge part of the critiquing process.  Without the actual phantom lateral skull images I use in all of my talks to prove my point, we are stuck with you just having to believe me. 

          I have taken my skull phantom and shot 9 different manufacturers to prove exactly how much mAs can be used and still have a passable image.  Depending on the vendor one can use from 10 - 100 times too much mAs and still have a perfectly passable image, if a visual check is the only guideline being followed.  This is why the EI numbers must be used.

          Sometimes a radiographer will “post collimate” or “shutter” an image which depending on the vendor may change the EI number.  As a huge side note, if any of the actual body is cropped out during this process, the image is now open for a lawsuit (see upcoming blog #4 on Feb. 15^th).

          Another “tool” to use is the magnification mode button.  Quite often burn or mottle can only be seen with the image, or part of the image, being magnified.

          The last “tool” to use is Level/Windowing.  Whether your facility allows you to Level and Window the image and send it to PACS, all departments should allow a radiographer to Level and Window and then reset it before sending it to PACS.  Whenever an image does not look perfect, one should always Level and Window it and see if the image can be made to look perfect (or at least much better).  If after Level and Windowing the image does not look better, it is impossible to know if the radiologist can make it look better.

          So as a quick synopsis, the 3 things that should be done to properly critique a digital image are:

1-    Check the EI number

2-    Use the magnification mode to check for burn and mottle

3-    Level and Window the image and either reset it or send it depending on your facility’s protocol

Back to DRS Website