Ceph too large?

[gerhard]

I recently saw a ceph that was about 25% too large, judging by the difference between its cm scale and the dentalcad grid. Does that still produce accurate measurements?

[anandhi]

If it is only to read the ceph it is OK ,But if we are doing VTO with that ceph then NO,we will not get correct VTO because the model measuring will be 25%less campared to the ceph

[DMcGann]

The vto is definitely distorted and could influence your treatment decision.  The angular measurements are probably ok, but the linear measurements of course are wrong.
   ALL DENTISTS THAT HAVE DIGITAL CEPH MACHINES should ASSUME that the machine is out of calibration.  Some manufacturers have made a program 'fix' (update) that corrects the calibration problem. Others still have not, and if the manufacturer will not make the necessary correction, then you should make the correction in adobe photoshop (not as accurate, but you can get close).
   TESTING to see if your machine is calibrated correctly or not is very easy. 
a) some machines have a millimeter ruler visible on the image.  You can either print and measure this directly, OR I put "condylion" on one side of the mm ruler and "A point" on the other side. The measurement will be found in "maxillary length" when you calculate the tracing. Compare how many mm on the ruler vs. the measurement. simple.
b) If no mm ruler, cut a piece of stainless steel archwire of about 20-40mm and measure it.  Tape it to the film casette, and measure the same way in dentalcad. 
   25% seems to be out of calibration more than I have seen. I remember one x-ray technician stating that ALL digital cephs are 10-15% smaller than actual.  I believe this is due to the setting in the machine of "72dpi" resolution (like a camera) vs. "96dpi", the standard for 1:1 images.

[ABuck]

Thanks Don, great Info!

A few days ago I had the same problem and the ceph (from an orthodontist) is noticeably smaller (more than15% ?). He probably knows this (patient only had referral for ceph) and did all the measurements, which I now can use to calibrate. 

[timbur]

Gerhard,  with Win 7 much of the ceph data is  "off the page/screen", and I usually go to the blue measurements tab in IP soft to view the data.  Is there any fix for this?  I didnt have this problem with win XP, but unfortunately that laptop died, and the replacement has win 7.
I know this is a different issue than the lack of 1:1 image ratio with digital cephs, but Win 7 makes it look like the ceph is too large to fit all the data in!!!

thanks for the help

[ABuck]

This is the ceph I mentioned above. It´s actually 15,3% smaller. This I determined by the steps Don advised (see pic). The measured distance should be 10mm but is actually 8,47mm. This gives me the amount I have to calibrate the ceph for measurements with dentalcad. I used condylion and A point, which I set beside the ruler,distance 10mm on the ruler, the measurement can then be read at maxillary length (8,47mm instead of 10mm). Hope this helps 

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[gerhard]

timbur,
I think your problem is NOT caused by Windows 7, but by one of the following:

1) Most likely: Printer setup: if your default printer page is less than "Letter" size, change it to one that is letter size in Control Panel, Devices and Printers.
2) Untrimmed ceph: crop the ceph in Dentalcad (NOT in Photoshop) before placing any points.
3) Screen size: If your screen is less than 13 inches, it may cut off portions in Dentalcad or Ipsoft.
4) Screen resolution: set it to 1024 x 768.

Let me know if you need more detailed instructions for any of this.
Gerhard

[gerhard]

About judging if a ceph is correctly sized: if it has a mm ruler, I simply turn on the grid in dentalcad and compare that with the ruler. If they do not match, then I change the dimensions in Photoshop or with the free irfanview software, until it is correct. I also change its resolution to 96 dpi; and color to grayscale to make the file smaller on disk - this will result in smaller export files.

[DMcGann]

Andrew Buck, you got it. Unfortunately a lot of the ruler was cut off...I like to get the longest I can. 40mm is better than 10mm, but 10mm works. 
   EVERYONE, the quick check to see if a ceph is too small is to look at the TEETH in dentalcad tracing. If they are TOO BIG, the apices out the bottom of the mandible or out the top of the maxilla, you have a problem. The teeth in BUCKS ceph are out of proportion.
   Gerhards idea of turning on the 'grid' is good. I have a hard time reading the mm notches myself...magnifying glass for the old man?

[timbur]

Gerhard, the recc resolution on my laptop states:  1920 X 1080.  Will that cause a problem with dental cad and seeing all the data below the ceph?

[gerhard]

timbur, try 1024x768. If that does not help, it's probably your printer setup. If no improvement, please call our office so we can look at your computer remotely.

[terryrose]

In Australia most cephs and OPG’s are out sourced to radiology centres where the patient can get the image done for no fee (paid for by the government). Frustration with needing to resize cephs led me to buy my own digital ceph OPG machine (Vartech). I also checked prior to purchase that it did indeed provide a 1:1 ceph image.

It took me a while to master the resizing of cephs initially.  The process is time consuming if you have to do it often.

There are some great ideas in this thread:
-   using the grid as a measurement guide
-   using 40mm (if available) on the ruler vs 10mm for more accuracy
-    using the ceph tooth size vs IPSoft tooth size (which usually alerts you that there is a disparity in sizing if they differ)

Don this last idea of using tooth size disparity (ceph tooth vs IPSoft tooth) for resizing may have some merit (where there is no ruler for calibration).  If so would you use the upper or lower incisor? My guess the upper incisor but the lower incisor may be a little clearer on the ceph.

It seems tedious to have to go through the whole ceph tracing even when you know there is an obvious size discrepancy- ie. It would be nice just to place two points at the start on the ruler to gauge the size of the film and calculate (to work out the magnification factor) to save time.

One tip- when I have done my first ceph tracing I usually make a quick copy of the ceph and move the condylion  and A (or Gn) points on the second ceph to the ruler and calculate, to save mucking up the first one. You can always delete the second ceph if you want or just leave it in your records.

I know there are no plans to make any changes to IPSoft in the near future, but an ability to quickly calculate (with a couple of measurement points) and resize a ceph within IPSoft would have to rank high on the list of desired features.

Regards Terry Rose

[croberts]

If your cephs are coming from the same x-ray source once you have determined the correct adjustments, the process is usually very fast.
I use photoshop elements ( the cheap version - about $100) I also use photoshop to import my torque template overlays.
Import ceph into photoshop, click on "image" then  "resize" and change resolution to 96 and then change pixel width to 1000, click 'save as' and save as a tiff file into the patient's file.
This is then imported into dentalcad.
The first few times you do it, you need to check your calibration as described previously, but  as soon as you place the incisor, you know if you are close or not.
Once you have worked out the correct adjustments for your machine, it is quite fast and reproducible.

It is important that the ceph is corrrect, since this has a direct bearing on our VTO. If our VTO is incorrect then our ability to use the torque templates is reduced and therefore our diagnosis is compromised.

Campbell

[gtakenaga]

I have a digital Ceph machine and the image is about 10% too big. I spoke with my manufacture (Instrumentarium) and at this time, 1:1 calibration cannot be done with their machine. My problem is that my images from this machine were even bigger 3 years ago and then after some update and maintenance 1 year ago the image are slightly smaller but still too big. The worse part now is when I do VTO overlays the images do not match up size-wise. Needless to say it was driving me crazy trying to make progress or finishing VTO overlays. HOWEVER!

I FOUND A SOLUTION! AND IT IS SIMPLE

I cannot take credit for this solution. This solution came from someone who works with Gerhard. I do not remember his name.

Solution: 1. original ceph needs to have a ruler on the image in millimeters. See picture below.
             2. open original ceph in dentalcad
             3. go to view > Grid  Lines. The grid line in centimeters with millimeters markings will show up   
                 superimpose onto the ceph. Click and hold Ctrl + Shift to move the ceph to line up
                 your ruler to the gridlines. Check the calibration of the gridlines to the ruler on the original
                 ceph. If they do not line up then your calibration is off. See picture below.
             4. Download IrfanView at www.irfanview.net
             5. Open digital image of ceph in IrfanView
             6. Go to Image > Resize/Resample > set width to 885 pixels and preserve aspect ratio. It
                 is possible you will need to play with the width settings to get the correct calibration. Save
                 the image with the new settings.
             7. Upload the calibrated ceph to dentalcad and repeat above steps to compare the gridlines with
                 the ruler markings. Adjust the width again if it is still off, but otherwise you should be done
                 and have a ceph that has 1:1 ratio for accurate measurements and more importantly be able
                 to do VTO overlays accurately.

[ Attachment: You are not allowed to view attachments ] This is an example of one of my digital ceph. The ruler is mounted on the nose piece of the ceph machine.


[ Attachment: You are not allowed to view attachments ] This images is a close up of the ruler on the ceph with the markings not able to line up with the grid lines. The first centimeter gridline is lined up but the second gridline one is about 5% off and the third gridline is 10% off.

[ Attachment: You are not allowed to view attachments ] This image is a close up of the ruler on the calibrated ceph with the markings that are now able to  line up with the grid lines. Width = 885 pixels, preserve aspect ratio.

I hope this helps,
Glenn

[DMcGann]

I just received my first 3D ceph image, taken for a POS instructor at a 3D imaging center. 
1. Calibration was too large:  by Co-A method, 100mm measured 126mm
2. Also confirmed by Derek (Brian Liao) grid method, 40mm measured approx. 50mm
3. VERY DIFFICULT to see the structures of the palate and lingula symphysis of the mandible.
4. EASY to read nasion, porion, condylar head, orbitale.
5. Nose soft tissue was 'broken", so hard to trace smoothly.
6. Numbers cover the ceph image.  The screenshot below was the full screen, I could not show you the full face.  When numbers cover the image, you need to "crop" any unnecessary stuff (eg. brain) in dentalcad after importing.  Filter-rotate, adjust size of dotted line, crop, ok.
7. there is ONLY 1 page (numbers do not go to second page) for model measuring and Ceph, which includes the image + numbers.  If you scan or do not crop vertically, you may get the numbers on top of the image. To edit the part under the numbers, you need to turn off nomenclature (check box on left), make edit and do again since keeps coming back!
8. File was VERY LARGE, with the starting import of the case being 57Mb and my ending size after more dental vto (copy of the ceph) being 127Mb.
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