Saturday, October 26, 2013

dRs New Blog - FeedBurner Reply
 
Just needed to tell you that if you  subscribe to the blog again on the newly designed website, make sure you answer the email from FeedBurner that will come almost immediately.  Many of us didn't see it or it got spammed, but it needs to be replied to so that the site knows it has your correct email address.  If you have resigned up but don't get an email about the next blog post on November 1st, then FeedBurner didn't get it.
 
Thanks.
 
Dennis


 

Saturday, October 5, 2013


SPECIAL NOTICE         I HAVE A NEW WEBSITE              10/5/13

Hi Everyone,
 
I'm not sure if this notice went out to you about the new Website.

As of September 30th I have a completely remodeled website.  The Blog is now part of the actual site and not here on Blogspot.  This is all wonderful news except the RSS feed subscribers didn't come across from Google.  This means if you subscribed before and would still like to get the bi-monthly notices, you will have to go to my new site and subscribe one more time.  Sorry about that, but there was no getting the info from the Google folks.  The web address is exactly the same at digitalradiographysolutions.com

If you read the new blog I wrote for today on that site, it will explain almost all of the cool things the new site has that the old one didn't. 

So thanks for all your support in the past and I hope it continues into the future!!.

With Lots of Humble Gratitude,

Dennis

Monday, September 30, 2013


SPECIAL NOTICE         I HAVE A NEW WEBSITE              9/30/13

Hi Everyone,

As of September 30th I have a completely remodeled website.  The Blog is now part of the actual site and not here on Blogspot.  This is all wonderful news except the RSS feed subscribers didn't come across from Google.  This means if you subscribed before and would still like to get the bi-monthly notices, you will have to go to my new site and subscribe one more time.  Sorry about that, but there was no getting the info from the Google folks.  The web address is exactly the same at digitalradiographysolutions.com

If you read the new blog I wrote for today on that site, it will explain almost all of the cool things the new site has that the old one didn't. 

So thanks for all your support in the past and I hope it continues into the future!!.

With Lots of Humble Gratitude,

Dennis

Sunday, September 15, 2013


# 18                       Image Gently/Image Wisely                     9/15/13

Today I’d like to tell you a little bit about two wonderful organizations; Image Gently and Image Wisely.  Image Gently was created first, in 2007.  In one sentence, their goal is, “to change practice: to raise awareness of the opportunities to lower radiation dose in the imaging of children”.  A couple of years later it was realized that this goal was also very important for all the rest of our patient’s who are not pediatrics, so Image Wisely was created.

The four groups of professionals that make up Image Gently and Wisely are: Imaging Technologist’s, Imaging Physicians, Medical Physicists and Nuclear Medicine Tech’s.  As of today’s post, there are currently 20, 831 members of Image Gently and 18,825 members of Image Wisely.

I joined both organizations a few years ago as soon as I was introduced to them.  Their entire goal is for the imaging professional to give better patient care, and what is more important than that?  At the end of this post I have attached a copy of both the “pledges” that one would make if you decide to join.  They are from one of the last slides I present in my 6 and 8 hour talks.  I can guarantee you that NO ONE will EVER contact you or use your phone number or email address.  All they want is for you to believe in the pledge and try your best to conduct your professional life accordingly.  Also the totals of the members will increase, showing both the professionals and the patient’s that there really are a lot of us that truly believe in great patient care.

One of the really incredible things about the Image Gently site is the section they have for parents.  In it they can find well written, non technical descriptions of the scarier exams children sometimes have to go through.  These include; contrast enemas, UGI’s, VCUG’s, CT’s, interventional exams and Nuclear Medicine exams.

 I'll let the pledges speak for themselves.  If you agree with them, I would love to see you join us.  You can click here to get to Image Gently and her to get to Image Wisely.
 
 

Sunday, September 1, 2013


#17                         The 15% Rule and the Not So Famous Bowman’s 7 ½% Rule                              9/ 1/13

 

     I believe the 15% rule was figured out in the mid 50’s.  Of course this was back in the days of film/screen, but it still holds true today in the digital world.  
     The “Rule” stated that if you increase any given technique by adding 15% more kV the following film would have twice the density/opacity (which we will now just call opacity) as the original film.  And that’s all there is to the rule. 
     Now what most people have done with it is cut the mAs in half after they increased the kV 15%, but that’s now an addition to the 15% Rule (which we will now call the 15% Rule with mAs compensation).  And a great addition it is.  It was a way to change the technique but still end up in with basically the same opacity that you started with.  This is because when you increase the kV 15% the film was double the perfect opacity from what you wanted, but then by cutting the mAs in half you also cut the opacity in half thereby ending up right where you began but with a new technique.
     What must be mentioned here is from the many experiments I performed on both the 15 and 7 ½% Rules (I'll get to that one), the Exposure Index (EI) number stayed the same or was very close.  This means that after changing the techniques with either or both rules your EI number will still be correct!!
     There are really 2 main reasons why someone would do the 15% Rule with mAs compensation.  The first is to cut the patient dose.  To read more about this, please refer to Blog #12 from 6/15/2013 (How Low Can You Go?) where I explain that by increasing 15% more kV and cutting the mAs in half you can save your patient almost 33% of the Entrance Dose!!
     The second reason would be to cut the time for the exposure.  This is really only needed on portable machines that have a built in 100 mA station (which is most portables on the market).  100 mA means if your technique has 200 mAs then your exposure time will be 2 seconds, a 50 mAs exposure would be ½ a second and so on.  This usually happens when doing portable abdomens on a patient who is unable to follow breathing instructions and your exposure time is over ¼ of a second long.  I’ve always taught (even back in the film days) that an image taken out of the optimum kV range which is possibly or even definitely longer scale (greyer) than normal is always better than an image with motion.  In my opinion the only thing worse than motion is actually cutting off the anatomy.
     So now let’s quickly discuss the not so famous (yet!!) Bowman’s 7 ½% Rule.  As you will see it is simple and easy to do and quite often the perfect thing to use when changing techniques.  In a nutshell, all we are going to do is use half of the 15% Rule.  Since it’s easier to see it with actual techniques, let’s start with:

80 kV @ 40 mAs

92 kV @ 20 mAs = 15% Rule with mAs compensation

86 kV @ 30 mAs = 7 ½% Rule and cutting out a quarter of the mAs

     All that you need to do is first figure out what 15% of the kV is and what half the mAs would be and then just use half of each.  As you can see from the above example; 86 is exactly between 80 and 92 and 30 is exactly between 40 and 20.  With film all three of these techniques would have had the same basic opacity.  In the digital world (both CR and DR) the EI number will be the same.
      So why would use the 7 ½% Rule?  If you are still using low kV/high mAs techniques and now are willing to change, sometime doing the 15% Rule with mAs compensation will still not increase the kV high enough.  But if you did it all again the kV would now be too high, but just doing the 7 ½% Rule will be perfect.  Using the same example from before we see:

80 kV @ 40 mAs

92 kV @ 20 mAs = 15% Rule with mAs compensation

106 kV @ 10 mAs = 15% Rule with mAs compensation

99 kV @ 15 mAs = 7 ½% Rule and cutting out a quarter of the mAs

     So if you decide that you are unwilling to go above 100 kV for a particular shot, then using the 7 ½% Rule would be perfect as it takes you to 99 kV.  Of course this works with any starting kV or mAs and is applicable anytime you don’t want to increase your kV a full15%.
     If you have problems figuring out 15% of a number, I have a chart already made that shows 15% from 50-120 (see below).  To download this chart, go to: http://digitalradiographysolutions.com/files/29_kV%27s_and_the_15%25Rule.pdf   There also is a column that shows how much more opacity would be added if just 1 kV was added.  I have a whole discussion on that column in my full day lectures, but since that would take another page, for now I’ll just call it a day.


     kV
15%
1 kV =
50
7.5
13.30%
60
9
11.10%
70
10.5
9.50%
80
12
8.30%
90
13.5
7.40%
100
15
6.60%
110
16.5
6.00%
120
18
5.50%

Thursday, August 15, 2013

#16    Why Should You Increase the SID for Abdomen’s?               8/15/13

     For the first 10 years of my career (late 70’s, early 80’s) the SID for abdomen x-rays was 40” and that was written in stone.  I still remember the first new GE room we got at Watsonville hospital that had a 44” detente.  It seemed blasphemous that a company would think, much less do, such an outlandish thing.  Was nothing sacred?
     Then about 6 or 7 years ago one of our students told me that he had just come from a facility that did all of their supine abdomen x-rays  with the tube as high and table as low as possible and their upright’s were done at 72”.  Needless to say this seemed unbelievable to me but here was an x-ray department in my own area that had obviously been doing it for quite a while.  He explained that they did it because with the greater SID there was less divergence, so more anatomy was seen.
     Now that I knew this was even possible (and ethical), I asked our radiologist’s what they thought about it.  It turned out they loved the idea.  Since their entire job is to make a diagnosis with the information given to them, the more information they have to work with the better they like it.
     So I decided to do a simple experiment to see exactly how much more anatomy we would see when we increased the SID.  I took my abdomen phantom and exposed it at 40”, 50”, 60” and 72”. 
     As you can see in Figure 1,
at 40” the top of L1 is at the very top of the image and there's about a marker’s width below the ischial tuberosity at the bottom.  There is also just over a markers width on the sides. 
     In Figure 2, at 50”
we can now see about one third of a vertebra of room at the top and a marker and a half at the bottom and on the sides.
     In Figure 3,at 60”
we can now see about half of a vertebra at the top and a marker and three fourths on the bottom and sides.
     Finally in Figure 4,
at 72” we can now see a solid three fourths of a vertebra of room at the top and two markers on the bottom and sides.
     Since a vertebra is approximately one and a half inches in height, this means we gained at least two and a half inches of extra anatomy top to bottom and just under that on the sides.
     Plus there is a second reason to use a greater SID and this is to save the patient entrance dose.  Or at least I believe this is so.  I am almost positive I have read an article in the ASRT Journal that stated that an increased SID 40" to 4*"") would save a patient about 8% entrance dose.  Unfortunately when I went to look up that article for this posting I couldn't locate it.  If any of you know about this dose savings article, please write or call me and I'll let everyone know about it in my next blog or somewhere on my website.                     
     Whether there really is a dose savings or not, getting close to 3 more inches of anatomy on an upright abdomen surely is worth talking to your radiologist about this.   Just remember that the more SID you have the higher you need to center so that all the new anatomy you are showing is the upper abdomen and not the symphysis or below.
     If you are taking these images portably and need to technique it, remember that the mAs will need to be increased as the distance is increased.  If you want to know exactly what these changes are, please use the “exp-dist conversion” chart below (and located in the All Charts section of my website). 
 

Thursday, August 1, 2013

#15       My Version of the Perfect Exposure Index (EI) System         8/1/13

     The chart below is a system that Agfa has implemented with all of their new equipment.  It’s a three color system with green being “within range”, yellow being “slightly over or under exposed" and red being “significantly over or under exposed”.  I like that they took a stab at it, but think that they went the opposite of the AAPM in that their ranges are too wide open (see blog # 14 for the AAPM’s ranges).  The green (within range) goes from 15 to 60 mAs and 60 is quadruple 15.  I like that the yellow zone on the overexposed side is only from 60-90 mAs but don’t really like that one needs to be 4 times their perfect 30 mAs or 8 times their bottom of the green 15 mAs to get to a place that is deemed significantly overexposed.



   


     The chart above is the one I created to fix the problems I saw with both the AAPM and Agfa models.  I’ve used a 7 section/color system as I do not think it’s a great idea to have the same color for over and under exposures (for those radiographers who are just looking at the colors and not the numbers).  I’m not sure how difficult it would be to implement 7 colored light bulbs or filters in the control panel, but it would be the best set up and easiest to use and understand.
     The reasons for the 7 sections instead of Agfa’s 5 is the radiographer can really fine tune their technique skills and get a much better understanding about how an EI number that is noticeably off can still look perfect.  Keeping a nice tight range as to what is Very Good versus Within Range versus Significant and finally Excessive is the only way to truly combat Dose Creep.
     I’ve put the green/Very good from a perfect EIT to +60%, or 2 normal steps up in mAs.  From 61% to 100% (double the mAs) is the blue/Within Range.  From 101% to 199% (double to triple) we’re now in the yellow/Significant region and from 200% up we’re in the red/Excessive zone.
     If you remember from my last posting, I wrote about the Deviation Index (DI) number and that it quantifies how much the EI varies from the TEI.  So unless the EI number comes out perfect (identical to the EIT) there will be a minus or plus DI number.  It’s A great idea to have this EIT number, but what help is it if you now know that your exposure was a +4 but it doesn’t tell you how to fix the technique?


     So my colleague Carter Doupnick and I created the “How to Fix an Incorrect mAs” chart you see above.  To use it you start in the middle column with the mAs that was just used (either by manual technique or with the AEC).  Then you use the plus or minus rows depending on what the DI number was.  Let’s say it was a +4 and the mAs used was 63.  When you match them up you see that 25 mAs should have been used.
     I am hoping that every vendor starts using this “How to Fix an Incorrect mAs” chart as it really is the only way that a DI number will actually be useful to a radiographer.  With it, every repeat that needs to have the technique changed will be incredibly easy to accomplish.  It won’t matter one bit if you’re good or bad with math as all the calculations have already been done.  Plus all techs and students will be able to use this chart to see what would/could have been the perfect technique even though the image taken was perfectly diagnostic, but still over or under exposed.
     If you’re facility is using any of the newest equipment that displays the DI number and you’re wondering what to do with it, please contact me so I can set your department up with this chart and system.

 Link to Digital Radiography Solutions Websitedigitalradiographysolutions.com

Monday, July 15, 2013

#14    The New Exposure Index (EI) Terminology  7/15/13

     There are three new definitions all of the manufacturers are now using that will soon become standard terminology in our profession.  The first and most important is that finally(!!) there will be only one name for the number that comes up after your exposure to show the measure of the radiation in the Region of Interest (ROI).  It will now be called the Exposure Index (EI) number.  This means the S, EXI, LgM, DEI and ReX numbers will be vanquished forever.   Yayyyyy!!!!  
     The next term is the Target Exposure number (EIT) and this will be the EI number when an image is optimally exposed.  Or in other words, the perfect goal EI number you are shooting for.  Since every facility will have different ideas on what is a perfectly diagnostic image, these target numbers will be determined by each facility depending on body part, view, procedure, image receptor and radiologists.
     The third term is the Deviation Index (DI) number and it quantifies how much the EI varies from the TEI.  So unless the EI number comes out perfect (identical to the EIT) there will be a minus or plus DI number.
     Now we get to the big problem though.  A few years ago the American Association of Physicist’s in Medicine (AAPM) came up with an EI system that all the manufacturers were going to use with their CR and DR equipment.  This was the Task Group (AAPM TG) 116 report issued in 2009.  Unfortunately their system was not really useable in the real world and none of the vendors implemented their plan (or at least the whole plan). 

     The picture above shows what the AAPM plan looked like.  The image has 4 distinct lines of information.  At the bottom in white I have put in different mAs’ so you can easily see the difference between each DI number.  I could have picked any mAs as the starting place so I chose 30.  The colored circles show the plus and minus DI numbers.  The system was set up so that a +1 DI number would be one average step up in mAs, +2 would be another step in mAs and +3 would now be one more step in mAs (or doubled a DI of 0).  You can see this in the black numbers just under the black line.  At the top is the place where the AAPM went off course.  Here is where they actually quantified how many DI numbers would be over or under exposed and what would be a repeat or excessive.
     I personally love that they want to set a standard but the ranges they gave were just impossible to uphold with the current equipment we use.  From all of the experiments I have performed on corrupting an EI number with incorrect positioning or collimation, I have seen up to 75% number changes, even though the same technique was used.  So to say that a +3 DI number would be excessively overexposed can really be just slightly overexposed but had really bad collimation and or positioning.
     So all the manufacturers realized that this system was too unforgiving.  The DI part of it was great, but how many plus or minuses make a repeat or is excessive will have to be decided in each facility. 
      In my next blog on September 1st I will discuss my version of the perfect Exposure Index system.

Monday, July 1, 2013

mAs = Dose

#13                                 mAs =  Dose                            7/1/13

     Today’s post will center on how the mAs you use is directly proportional to the dose you are giving your patients.  I could have just written “the dose the patient is getting” but I really want to make it clear that you the radiographer, or radiographer student, are the one setting the technique and making the exposure.  This is true whether you are actually setting a technique (both mAs and kV) or using an AEC and just setting the kV.
     By directly proportional I mean that the dose increases or decreases to the exact degree that the mAs increases or decreases.  For example, if the mAs is increased from 10 to 20 (doubled) then the dose is also exactly doubled.  If the mAs is decreased by 50% (cut in half) from say 30 to 15 then the dose is also exactly cut in half.
     To prove this point to you, I am going to present an experiment I conducted a while back with my DUKE phantom (see image 1). 

I did the experiment to prove that both the EI number and the dose will directly change with the mAs, so you will see Agfa’s LgM numbers also annotated on the images.  For this article I will only be concerned with the Entrance Dose (ESE) that was annotated on the magnified images that go with each exposure.

On image 2,we begin with a technique of 4 mAs@117 kV and an ESE of 20.81.  
 









As we go to image 3, the mAs is doubled to 8 mAs@117 kV and the ESE is now 41.40.  If it had been 41.62 that would have been exact, but even so it is only off by 1.06%.
   









                               
Looking at image 4, the mAs is now doubled again to 16 mAs@117 kV and the ESE is now 83.0.  If it had been 82.80 that would have been exact, but it is only off by -0.48%.

   









On the final image 5, the mAs is now doubled again to 32 mAs@117 kV and     the ESE is now 166.0.  This ESE is exactly double.

     









I hope this proves to you that changes to the mAs are equal to the dose.  Because of this I have been telling radiographers and students that a great way to keep yourself from needlessly increasing the mAs is to call it dose.  By this I mean you would say "I am going to use 50 or 100% more dose" instead of saying more mAs.  The word dose has a lot more impact and energy to it while the word mAs is no big deal.

Saturday, June 15, 2013

# 12                  HOW LOW CAN YOU GO?                  6/15 /13

     This is how I teach ALARA (As Low As Reasonably Achievable) to all of my students and whenever I give any kind of talk on digital radiography techniques to students or techs.  It's all about using the smallest/lowest mAs possible so that the dose is as low as it can be.  This can only be done by using the optimum kV (see blog #7 "Optimum kV for DR & CR Equipment" from April 1), which is a noticeably higher kV than was used with film.  With a higher kV, less mAs can then be used.               
     This new technique is only the first step in discovering how low you can go, although by adding 15% more kV and halving the mAs the entrance dose to the patient will be cut by about 33%!!  With such a quick and obvious way to save a patient 1/3 of the dose, you would think everyone would want to be doing this.  The fact is though, that instead of techniques being at an all time low (about 75% of the country now uses digital equipment which can employ lower doses than film) mAs/Dose Creep has occurred.  To read more about that, please see my first blog " The Problems of “CreepingmAs/Dose” in America" from January 1.
     The second step is knowing how perfect the image needs to be.  Some radiologist's want an image with absolutely no noise/mottle in it while others are absolutely fine with a little bit of noise.  In fact, the radiologist's at my hospital (Community Hospital of the Monterey Peninsula - CHOMP) want to see a little bit of noise.  This is called acceptable mottle and they actually dictate this term into their reading.  They know that by seeing a little bit of mottle we truly are taking the mAs/dose as low as we can go.  They also know that they cannot miss any kind of pathology with this small amount of noise in the image.
     I tell the students and radiographers that I would love it if they would make getting the lowest mAs a competition.  It is total bragging rights for whoever can use the lowest mAs for any given body type/size.  As the software in our digital computers allow for an inordinate amount of over radiation and still get a get a perfect looking image (automatic rescaling), the skill of "technique-ing" is becoming a lost art.  To see this first hand, go to the archive section in my Current Research and look up "Howmuch can you over-radiate and still get a perfect image?". 
     Basically anyone can use too much mAs and still have a perfect image every time, so that doesn't really take any talent.  What does take real technique-ing skill is to make an exposure that is very close to whatever Exposure Index (EI) number shows that the minimum amount of radiation was used.  My goal is to go for the perfect EI number to 50% more than that number.  If I am in that zone I know I nailed it!!


Saturday, June 1, 2013


# 11       Supertech is our newest advertiser        06/01 /13

     Today's post is going to be a bit different than my usual fair of writing about  CR and DR.  Today I'm going to tell you about Supertech.  Although you may think I'm writing this about you,  Supertech is actually this amazing diagnostic imaging online store that is celebrating its 40th anniversary this year.
     If you've been to my website you know that I have two company's advertising on the right hand side of the home page.  The beauty of running my own business is I get to pick who I will do advertising with.  I decided when I founded the company and website it wasn't worth the money to have anyone on the site that I didn't have 100% respect for.  That's why I started with just 2 businesses, MTMI and the Ferlic Filter Co.  Now Supertech makes three.
     Needless to say, all great companies need a strong leader, and Supertech most certainly has that.  The president/CEO and owner is Judy McNitt-Mell, an amazing woman who started working with Supertech ten years ago.  Her father actually started the business back in 1973, owning just 10% of the company, but over the years ended up owning it outright.  In 2009, Judy's father retired and she took control of the company lock, stock and barrel.
     I've met Judy a few times over the years because I would see her in the vendors room at many of the largest radiology conferences around the country.  One can't walk through a vendor's room without stopping at her booth, because Supertech has so many different products they sell. 
     Here are just a few of them: X-Ray Technique Calculator, Anthropomorphic and Multi-Modality Phantoms, Quality Assurance Phantoms, Aprons, Barriers and Filters as well as pages of other products for CT, Ultra Sound, MRI and Nuclear Medicine.
     I had personal experience with Judy's wonderful customer care when I purchased ALL of our phantoms from Supertech many years ago.   We started with just the abdomen phantom, but a few years later we were able to acquire the head and neck, thorax, entire right arm, elbow and the wonderful "DUKE" quality control phantom.   I still remember thinking how incredibly knowledgeable  she was (and is!!) about all of these different phantoms considering how many different products they carried. Being the inquisitive guy I am,  I had grilled her as I wanted to know everything about every one of them.
     One of the things Judy is proudest of is the SPoRT Pediatric Sectional Phantom.  She had attended several meetings which addressed the topic of pediatric imaging.  The big push for "Image Gently" made her think that it would be helpful for the market if there were Pediatric Phantoms which would help new technologists learn how to image gently.  Telling someone what to do and having something for them to use in a laboratory setting are vastly different.  Judy knew that Computerized Imaging Reference Systems, Inc (CIRS) would have the engineers and physicists who could handle a tough project like this.  She was very grateful to CIRS for creating SPoRT and she is very excited about this product.


     

Wednesday, May 15, 2013


#10         Shamelessly Plugging My First Textbook      May 15, 2013

     My first published book just hit the stands (or would have hit the stands if there was such a thing as a bookstore anymore) this week, so I thought you the reader wouldn’t feel it was too inappropriate to shamelessly plug my baby “Adaptive Radiography with Trauma, Image Critique and Critical Thinking”.
     As some of you might know, I spent all of 2010 as the Subject Matter Expert (SME), writing and outlining the chapters and choosing the images for an Anatomy and Positioning Textbook for Lippincott, Wilkins and Williams.  At the end of the year the project was cancelled and so were my dreams of being a published author.
     A few months later I met an old acquaintance of mine, Quinn Carroll, who had just finished writing the first ever physics book for digital radiology– “Radiography in the Digital Age”.  In addition to his physics book masterpiece, he had also been writing a positioning book that would have all the “tricks of the trade” in it.  Or in other words, everything that is not in Merrill’s and Bontrager.  Those two books show how to position the average patient where our adaptive radiography book was created to show how to position someone who for whatever reason cannot move or be moved into that position.  Hence, you now need to adapt.
     When we met, his editor had just told him that he needed a lot more positioning tips and tricks, but he had written everything he knew.  So he offered me co-authorship of the book and I was back in saddle once again!!
     So I started putting together all of my information and Quinn rewrote the text to it.  For the next 6 months we kept this up and by the summer of 2012 we had the book finished.  Of course that is just step one in the long process that takes a finished manuscript and turns it into a book ready to be sold.  There were peer reviews, rewrites, artwork, etc…  So here we are just under a year later and the book is available for sale!!
     If you have already surveyed my website, you know that I have a section on the bottom menu bar called Adaptive Radiography.  If you’re interested in finding out more about the book, here is the place to do that:  http://digitalradiographysolutions.com/AdptRad.html


Wednesday, May 1, 2013


#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.