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.
Greetings from a North Carolina Radiography student :) I just stumbled across your blog tonight as I was looking to see who else is blogging in this field. I'm a first year (second semester) student, and I blog my experiences also. I'm adding a link to your site from my blog (http://www.setzler.net/radiography) as well. I haven't had a chance to read everything you have posted here, but I plan to over the weekend. I have also created another site for radiography students that you may want to check out. It's at http://radiography.ning.com and it's growing. We have over 150 people registered so far, but the active people aren't quite that high in number.
ReplyDeleteJohn Setzler
Hickory, NC
Thanks for stopping by John... I'm looking forward to checking out your links over the next couple of days. I think a lot of people are beginning to blog about their experiences and some of the trade secrets they have learned, and I think it's great. Keep it coming!
ReplyDeleteThanks for stopping by John... I'm looking forward to checking out your links over the next couple of days. I think a lot of people are beginning to blog about their experiences and some of the trade secrets they have learned, and I think it's great. Keep it coming!
ReplyDeleteAt my current facility and at my previous position, the departments used the old film screen grids. Both were 6:1, with a FR of 40-72". I haven't used a caliper to measure a patient since school and rely on visual estimates to decide on whether to use a grid or not. A common non-grid technique that I use is 80KV@3-5MAS, and when using a grid, 110KV@6.4MAS. The CR system at my current job is an Agfa CR75, and the aforementioned techniques fell into the LGM range (1.7-2.3) the vast majority of the time, and at my previous facility which utilizes a Phillips PCR Eleva Corado those techniques are within the S-number range, 200-600 along with the images displaying useful diagnostic information.
ReplyDeleteNonetheless, I have experienced grid cut-off, on few occasions, due to incorrect tube position - mainly on exams for severely obese patients in the ER.
At my current facility and at my previous position, the departments used the old film screen grids. Both were 6:1, with a FR of 40-72". I haven't used a caliper to measure a patient since school and rely on visual estimates to decide on whether to use a grid or not. A common non-grid technique that I use is 80KV@3-5MAS, and when using a grid, 110KV@6.4MAS. The CR system at my current job is an Agfa CR75, and the aforementioned techniques fell into the LGM range (1.7-2.3) the vast majority of the time, and at my previous facility which utilizes a Phillips PCR Eleva Corado those techniques are within the S-number range, 200-600 along with the images displaying useful diagnostic information.
ReplyDeleteNonetheless, I have experienced grid cut-off, on few occasions, due to incorrect tube position - mainly on exams for severely obese patients in the ER.
I wouldn't worry too much about the caliper measurements or the focal range of your grids at this point, especially if you've got solid techniques that work. There are a couple of things you could try though. I've never tried this with Agfa, but I heard this at a seminar at UNC - try to avoid using grids with frequencies near the nyquist frequency (or half the sampling frequency of the Afga plate reader). Your Agfa vendor would be able to tell you the frequency if your QC person is not aware of it. You can also check to see if it's possible to change the sampling frequency of your reader. This would be especially helpful if you don't have the budget to purchase new grids.
ReplyDeleteExample: your 6:1 grid might have a frequency of 120 lpi and you acquire moire at a sampling frequency of 115, then you could either switch to a 100 lpi grid frequency, or adjust your reader scan frequency to 103 lpi. Make sure to check your scan frequency before you decide to purchase any SD grids to avoid this.
Even if you do either of these things, we still have to have good grid positioning during exposure, of course.
I wouldn't worry too much about the caliper measurements or the focal range of your grids at this point, especially if you've got solid techniques that work. There are a couple of things you could try though. I've never tried this with Agfa, but I heard this at a seminar at UNC - try to avoid using grids with frequencies near the nyquist frequency (or half the sampling frequency of the Afga plate reader). Your Agfa vendor would be able to tell you the frequency if your QC person is not aware of it. You can also check to see if it's possible to change the sampling frequency of your reader. This would be especially helpful if you don't have the budget to purchase new grids.
ReplyDeleteExample: your 6:1 grid might have a frequency of 120 lpi and you acquire moire at a sampling frequency of 115, then you could either switch to a 100 lpi grid frequency, or adjust your reader scan frequency to 103 lpi. Make sure to check your scan frequency before you decide to purchase any SD grids to avoid this.
Even if you do either of these things, we still have to have good grid positioning during exposure, of course.
"Your Agfa vendor would be able to tell you the frequency if your QC person is not aware of it"
ReplyDeleteSadly, that position was cast aside at every facility that I've worked shortly after they went film-less.
As for Agfa equipment, I haven't been impressed with their system, in any regard. Overall, I'd rate it adequate with fair image quality. I much prefer the Fuji and Philips CR systems.
Nonetheless, I appreciate your advice and wish I worked for a Director who was concerned about this type of issue, but that would be expecting too much. Also, I enjoy your blog and have passed on the URL to co-workers.
"Your Agfa vendor would be able to tell you the frequency if your QC person is not aware of it"
ReplyDeleteSadly, that position was cast aside at every facility that I've worked shortly after they went film-less.
As for Agfa equipment, I haven't been impressed with their system, in any regard. Overall, I'd rate it adequate with fair image quality. I much prefer the Fuji and Philips CR systems.
Nonetheless, I appreciate your advice and wish I worked for a Director who was concerned about this type of issue, but that would be expecting too much. Also, I enjoy your blog and have passed on the URL to co-workers.
Thanks for the kudos... It's possible that the scan frequency is listed somewhere in the operator's manual for the plate reader or in some other literature that accompanied the equipment when it was originally installed. I haven't known too many people who have used the AGFA system, but this is the first I've heard of any disappointment.
ReplyDeleteI'm wondering if your QA program representatives have elected an AGFA person to come in and perform the quality control for the CR sytem? A lot of vendors are doing this now with the service contracts written up during the purchase of new equipment.
In an ideal world, I suppose we'd all know exactly how to fix these issues, but then again, in an ideal world, you probably wouldn't have any problems at all.
Thanks for the kudos... It's possible that the scan frequency is listed somewhere in the operator's manual for the plate reader or in some other literature that accompanied the equipment when it was originally installed. I haven't known too many people who have used the AGFA system, but this is the first I've heard of any disappointment.
ReplyDeleteI'm wondering if your QA program representatives have elected an AGFA person to come in and perform the quality control for the CR sytem? A lot of vendors are doing this now with the service contracts written up during the purchase of new equipment.
In an ideal world, I suppose we'd all know exactly how to fix these issues, but then again, in an ideal world, you probably wouldn't have any problems at all.
I have been a Technologist for 18 years;however, I stayed at home for an extended period of time to raise my children. When I came back, I was pleasantly surprised to find that Xray became easier with CR. I also was given the position of part-time clinical instructor for the Junior xray class. I have forgotten some things about grids and had a very important question. It is my understanding that you cannot angle against the grid lines , or you will get grid cut-off. Several people at our facility do this, and I haven't seen any cut-off, yet. Why is this? We use AGFA. Is the computer compensating for it? Remember, I'm old school, CR is new to me. Thanks !
ReplyDeleteI have been a Technologist for 18 years;however, I stayed at home for an extended period of time to raise my children. When I came back, I was pleasantly surprised to find that Xray became easier with CR. I also was given the position of part-time clinical instructor for the Junior xray class. I have forgotten some things about grids and had a very important question. It is my understanding that you cannot angle against the grid lines , or you will get grid cut-off. Several people at our facility do this, and I haven't seen any cut-off, yet. Why is this? We use AGFA. Is the computer compensating for it? Remember, I'm old school, CR is new to me. Thanks !
ReplyDeleteVery interesting Nick... I have yet to see a CR system compensate for what should be a huge loss of image information (depending on how steep the angle of the tube is). I would be interested to learn a few things. How many degrees of tube angulation are you talking about on average, and in which direction vs. grid orientation? What is the grid ratio? You should have more lattitude in tube angle with lower grid ratios. Could you already using SD grids, or perhaps crosshatched grids?
ReplyDeleteMy bet is that you may be using very low grid ratios (5:1 or 6:1) and there is actually grid cutoff going on, but maybe not perceivable on the QC screen. If you had a 12:1 or 16:1 grid, you would notice an obvious difference even on the QC screen. If you get a chance to view the image on PACS, try magnifying it x 200% - 300% and zoom in on an area of the image that is closes to the x-ray tube when there was a tube angle placed on the projection. You may see some image noise (looks like quantum mottle - speckles of density). Whenever CR systems lack sufficient photons in an area of the image, noise should occur.
I have to say I'm not very familiar with AGFA, but I've heard some interesting things about it. Let me know what you find out... there should be (as I'm sure you already know) a sticker on your grids giving you the ratio and the grid type.
Very interesting Nick... I have yet to see a CR system compensate for what should be a huge loss of image information (depending on how steep the angle of the tube is). I would be interested to learn a few things. How many degrees of tube angulation are you talking about on average, and in which direction vs. grid orientation? What is the grid ratio? You should have more lattitude in tube angle with lower grid ratios. Could you already using SD grids, or perhaps crosshatched grids?
ReplyDeleteMy bet is that you may be using very low grid ratios (5:1 or 6:1) and there is actually grid cutoff going on, but maybe not perceivable on the QC screen. If you had a 12:1 or 16:1 grid, you would notice an obvious difference even on the QC screen. If you get a chance to view the image on PACS, try magnifying it x 200% - 300% and zoom in on an area of the image that is closes to the x-ray tube when there was a tube angle placed on the projection. You may see some image noise (looks like quantum mottle - speckles of density). Whenever CR systems lack sufficient photons in an area of the image, noise should occur.
I have to say I'm not very familiar with AGFA, but I've heard some interesting things about it. Let me know what you find out... there should be (as I'm sure you already know) a sticker on your grids giving you the ratio and the grid type.
I do know that our ratio is 10:1, but I will have to find out the other info. The angle is approx. 5 to 10 degrees. Like I said, I have been out for a while, but I am slowwly, but surely rmembering everything. Thanks for the help. I'll get more info. I have asked others in our dept. this question, but everyone is as puzzled as I am.
ReplyDeleteI do know that our ratio is 10:1, but I will have to find out the other info. The angle is approx. 5 to 10 degrees. Like I said, I have been out for a while, but I am slowwly, but surely rmembering everything. Thanks for the help. I'll get more info. I have asked others in our dept. this question, but everyone is as puzzled as I am.
ReplyDeleteGreetings from Buffalo, NY. It's very interesting to see what happens in other parts of the country-- we're having similar issues with grids. Question: we've had a problem with abusive surgeons since I started 15 years ago. How can I address this to my students?
ReplyDeleteGreetings from Buffalo, NY. It's very interesting to see what happens in other parts of the country-- we're having similar issues with grids. Question: we've had a problem with abusive surgeons since I started 15 years ago. How can I address this to my students?
ReplyDeletePS: I have an x-ray blog also at
ReplyDeletehttp://xraystories.blogspot.com which is more anecdotal. -Tim
Hi Tim,
ReplyDeleteI think we've all been verbally abused by a surgeon regardless of whether or not we did anything to warrant a verbal lashing... it's almost become a rite of passage for radiographers. I usually try to encourage students not to take it personally; water off a duck's back. The amount of stress they have to endure is insane, and I'm willing to bet that when you're not in there taking an x-ray or operating the c-arm, it's very possible that they are yelling at the next closest person about something that isn't their fault.
Still, if a surgeon "crosses the line", it should be mentioned to a supervisor so that someone with authority can address the issue.
Hi Tim,
ReplyDeleteI think we've all been verbally abused by a surgeon regardless of whether or not we did anything to warrant a verbal lashing... it's almost become a rite of passage for radiographers. I usually try to encourage students not to take it personally; water off a duck's back. The amount of stress they have to endure is insane, and I'm willing to bet that when you're not in there taking an x-ray or operating the c-arm, it's very possible that they are yelling at the next closest person about something that isn't their fault.
Still, if a surgeon "crosses the line", it should be mentioned to a supervisor so that someone with authority can address the issue.
I am curios to know,what causes the following on a ct scan. when there is an image and it looks like a flash of light coming from a particular point?
ReplyDeleteMany moons ago, when I did CT on a single slice axial machine, this type of artifact was called a "star" artifact, and could be seen around any metal objects or even barium that was used in fluoro studies. A picture might help, but I think this is what you were asking about.
ReplyDeleteI am sure that we are talking about the same thing. Another question, although aluminum is a radiolucent metal, would it cause the star artifact? Thank you for your earlier reply.
ReplyDeleteTypically, the higher the atomic # of the material, the more artifact it will cause on a CT scan. Aluminum should still cause an artifact on CT, but not as great of one as steel, for example. If you compare contrast studies from that of diagnostic x-ray exams to CT scans, you'll notice that CT requires it to be "watered down" so to speak. I don't know what they use now, but when I did CT for an abdomen/pelvis scan w/wo con, we would mix one ounce of gastro with 16 ounces of water, and have the patient drink two of those cups. If you did this for an upper GI, you would not have the concentration of contrast you need to visualize the anatomy with plain x-ray. You can also visualize a renal stone made of uric acid on CT, when you cannot on x-ray (typically). CT will be way more sensitive to those differences. I hope I didn't get side-tracked too much!
ReplyDeleteGreetings.. I'm a final year radiography student. I need help on project topics in radiation protection, ultrasound, conventional radiography and others. Pls I wld be grateful. Thank you.
ReplyDeleteWhat kind of help do you need?
ReplyDeleteThis comment has been removed by a blog administrator.
ReplyDeleteHi, I am a second year radiography student in England.
ReplyDeleteI have been seriously confused by a placement site of mine.
It uses DR
4m
out of bucky no grid
ABout 110KV and 5 mAs
While i understand the distance will result in mainly the primary radiation reaching the detector and little scatter, meaning you might not need a grid.
Could you do this technique at 2m which they were allowing me and other students to do?
Thanks :)
Hi, I am a second year radiography student in England.
ReplyDeleteI have been seriously confused by a placement site of mine.
It uses DR
4m
out of bucky no grid
ABout 110KV and 5 mAs
While i understand the distance will result in mainly the primary radiation reaching the detector and little scatter, meaning you might not need a grid.
Could you do this technique at 2m which they were allowing me and other students to do?
Thanks :)
Hi, i am a secon year radiography student and i have been extremely confused!
ReplyDeleteOne of my placement sites uses
DR
4m distance
no grid
110 kv and 5 mAs
while i can understand using the 4m distance means you don't need to use the grid as most of the scattered radiation would reach the detector.
I am confused as to why me and other students/ agency radiographers were allowed to do it at 2m? no grid out of buckey. they said they didn't do it in buckey because the grid wasnt removable? :S
Thank you for your help!
Lou
Hi, i am a secon year radiography student and i have been extremely confused!
ReplyDeleteOne of my placement sites uses
DR
4m distance
no grid
110 kv and 5 mAs
while i can understand using the 4m distance means you don't need to use the grid as most of the scattered radiation would reach the detector.
I am confused as to why me and other students/ agency radiographers were allowed to do it at 2m? no grid out of buckey. they said they didn't do it in buckey because the grid wasnt removable? :S
Thank you for your help!
Lou
Hi Lou,
ReplyDeleteYou know us Americans... not very used to the metric system. Are you saying that your source to image receptor distance is 4 meters? If so, that's not a standard where I'm at. We use 72 inches, which is just short of 2 meters for all our chest x-rays. For most of our other exams, we use 40 inches, or about 1 meter.
We keep chests around 2 meters because we want to reduce magnification of the heart. So we also make sure the patient is against the image receptor (no OID).
I think I may be confused (if you're talking about SID) why you might think the scatter would be much different with the same OID... can you elaborate a little more on your question?
Thanks, Jeremy
Hi Lou,
ReplyDeleteYou know us Americans... not very used to the metric system. Are you saying that your source to image receptor distance is 4 meters? If so, that's not a standard where I'm at. We use 72 inches, which is just short of 2 meters for all our chest x-rays. For most of our other exams, we use 40 inches, or about 1 meter.
We keep chests around 2 meters because we want to reduce magnification of the heart. So we also make sure the patient is against the image receptor (no OID).
I think I may be confused (if you're talking about SID) why you might think the scatter would be much different with the same OID... can you elaborate a little more on your question?
Thanks, Jeremy