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Old 05-07-2008, 01:08 PM   #1
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DEXA Scan vs. QCT

Has anyone heard of measuring bone density with a Quantitative Computed Tomography (QCT)? I just stumbled across this and thought I would ask the group. The literature that I read stated that QCT is a more accurate way to diagnose osteoporosis.

Am I correct that there is no test out there that actually measures bone strength? The DEXA scans measures density, but that isn't necessarily bone strength.

Thanks for your (advanced) input!

 
Old 05-07-2008, 07:42 PM   #2
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Re: DEXA Scan vs. QCT

I just recently had a QCT as a conventional Dexa cannot be done on my spine (being fused with titanium all the way from my sacrum to my neck). It was difficult finding a facility that even knew what it was, much less performed it. The QCT, apparently, is capable of reading around the metal. I do not know how the numbers correlate with the Dexa t-scores but the ortho was pleased with what he saw (let's hear it for Forteo!)
Don't think it is any more a measure of bone strength than the regular scan.
Good luck!







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Old 05-08-2008, 09:56 AM   #3
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Re: DEXA Scan vs. QCT

Hi yef and turtlelady: Turtlelady, congrats on the Forteo, that's fantastic...

I've had 2 QCT's and 1 DXA, and was told that the QCT overestimates the score and the DXA underestimates it. Here's a link from the Univ of WA that explains it. After you get to the initial page and find the QCT para, then continue to see the differences between QCT scores and DXA.

I also have hardware in my lumbar area, but that isn't the reason I had a QCT. Where I live they only had the QCT 5 years ago, while now they have both. You should know that the QCT does a 3d measurement, but the down side other than the overestimation is that it emits a *lot* of radiation.

When I had the DXA done they couldn't scan the area where I have rods and screws, so I have 2 different scores that *can't* be compared. If you want a QCT, make sure that you realize that in the future you can only compare them to another QCT, not a DXA. Hopefully in the future they will eliminate some of the problems with QCT, because it does scan around titanium, and does the 3d picture, but they are hard to find now, since the DXA is considered the gold standard.

So far there isn't a test for bone strength, so we'll have to wait for that.

[url]http://courses.washington.edu/bonephys/opbmd.html#WHO[/url]

(continue through the pages to read the graph on QCT scores v DXA scores.)

Last edited by DesertBloom; 05-08-2008 at 09:59 AM.

 
Old 05-09-2008, 08:40 AM   #4
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Re: DEXA Scan vs. QCT

Thanks, Desertbloom for the web link.

For the time being, I think I will stick to my DEXA scan for my next test. I look forward to the day that they can measure bone strength.

Yef

 
Old 05-12-2008, 01:29 PM   #5
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Re: DEXA Scan vs. QCT

Actually there is a test for bone strength; just apply increasing mechanical force to the bone until it breaks. Such a study was recently done (using bones from cadavers), with the results presented in the article "Evaluation of trabecular mechanical and microstructural properties in human calcaneal bone of advanced age using mechanical testing, microCT, and DXA". MicroCT was a better predictor of bone strength than DXA, but the best predictor of bone strength was the trabecular number. So even if your bone density is increasing, you could be losing bone strength if your trabecular number is decreasing. It's better to have a bundle of many thin twigs instead of a bundle of a few thick twigs.

 
Old 05-15-2008, 04:31 PM   #6
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Re: DEXA Scan vs. QCT

Quote:
Originally Posted by PikaB View Post
So even if your bone density is increasing, you could be losing bone strength if your trabecular number is decreasing.
So....I'm confused....if we're going by T-scores alone, how do we know if our trabecular # is increasing? Is there a new type of DEXA machine that measures trabecular BMD as well as overall BMD?

 
Old 05-16-2008, 05:37 AM   #7
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Re: DEXA Scan vs. QCT

The "trabecular number" has nothing to do with BMD; it is the average number (count) of trabeculae in a given volume of bone. It is cannot be measured by DEXA.

 
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