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Home > Archive > Radiology > January 2005 > CT
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| Hello,
i have to undergo abdominal and pelvic CT and they told me it would be
done using both oral(3% Hypaque) and IV(Omnipaque) contrast.In the
hospital told me to come day earlier to drink one half of the oral
contrast,for better opacification of the bowel,and the other half
couple of hours prior to the study.Isn't taking of the first half of
the oral contrast a day before a bit too early?Every single
abdominal/pelvic CT protocol i read says oral contrast is taken 3-4
hours prior to the study(whole quantity)
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| Danny wrote:
> Hello,
>
> i have to undergo abdominal and pelvic CT and they told me it would be
> done using both oral(3% Hypaque) and IV(Omnipaque) contrast.In the
> hospital told me to come day earlier to drink one half of the oral
> contrast,for better opacification of the bowel,and the other half
> couple of hours prior to the study.Isn't taking of the first half of
> the oral contrast a day before a bit too early?Every single
> abdominal/pelvic CT protocol i read says oral contrast is taken 3-4
> hours prior to the study(whole quantity)
>
When do they take a scout film?
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| Joseph 2005-01-27, 8:43 am |
| This is quite interesting. Could you please share the reasoning for
this after your exam?
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| richard.epstein@alum.mit.edu 2005-01-27, 8:43 am |
| The reason to take the oral contrast the day before is to give it time
to get all the way through the colon.
Usually you drink it the night before, about 12 hours before the test.
So people will get the contrast to
the colon after only a few hours, but a lot of the time you don't get
good bowel opacification without the contrast
the night before.
Many protocols don't give contrast the night before for practical
reasons. i.e. You have to make an extra
trip to pick up the contrast, Emergency studies cannot wait 12 hours,
etc.
Worst comes to worst, in some people the contrast from the night before
might have already gone through the
colon and been passed.
In the case of oral contrast, there is no "scout" film (image without
the oral contrast). Since the oral contrast
is contained within the bowel, this usually doesn't cause confusion.
I have seen an appendicolith (stone in the appendix) missed because of
oral contrast. Some centers don't give
oral contrast for all cases - for example when looking for a renal
stone.
-Rich
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| richard.epstein@alum.mit.edu wrote:
> The reason to take the oral contrast the day before is to give it time
> to get all the way through the colon.
> Usually you drink it the night before, about 12 hours before the test.
> So people will get the contrast to
> the colon after only a few hours, but a lot of the time you don't get
> good bowel opacification without the contrast
> the night before.
>
> Many protocols don't give contrast the night before for practical
> reasons. i.e. You have to make an extra
> trip to pick up the contrast, Emergency studies cannot wait 12 hours,
> etc.
Yes, my understanding is that you give the patient barium enema for a
colon exam rather than oral contrast on the same day of the exam.
Plus, if you administer the contrast orally, you may find residual
barium in the small intestine in the same film as well. The image with
the colon superimposing with the small intestine -- how good is it for
diagnosis?
> Worst comes to worst, in some people the contrast from the night before
> might have already gone through the
> colon and been passed.
>
> In the case of oral contrast, there is no "scout" film (image without
> the oral contrast). Since the oral contrast
> is contained within the bowel, this usually doesn't cause confusion.
I thought scout films were necessary for all exams with contrast.
> I have seen an appendicolith (stone in the appendix) missed because of
> oral contrast. Some centers don't give
> oral contrast for all cases - for example when looking for a renal
> stone.
For a kidney stone, contrast has to be injected intravenously.
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| Rich,
thanks for the answer.What worries me,is that my docs suspect chronic
appendicitis,and that's one reason why i am undergoing CT.I surely
don't want to pass all of my oral contrast and ruin the exam!If i take
Oral contrast some 4-5 hours prior to the exam,will it provide good
opacification of the small bowel?
Dan
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| richard.epstein@alum.mit.edu 2005-01-27, 8:43 am |
| I agree with Andrew. Protocols differ by center, and in the end, it
often doesn't make a lot of difference.
I've diagnosed appendicitis without IV or oral contrast. I've seen it
missed with both oral and IV contrast. It's normal to have the contrast
in both the small and large intestine. They will not "overlap" on the
CT images.
Do what your doctor (radiologist) requested. They're the ones who need
to read the study.
To another poster - we don't always get pre-contrast images in CT.
Mainly because of time and radiation dose.
Many chest and abdomen/pelvis studies are done only post-contrast.
To another - some sites don't inject (or give oral) for a kidney stone.
IV contrast in the collecting system of the
kidney can obscure a stone. Other places like it, it can help find the
ureters and help see if there is
hydronephrosis. We used to do a non-contrast study and if that didn't
answer the question, follow with
an iv contrast study.
-Rich
-Rich
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