Hi, this is Pam Johnson an, I'd like to present my second resident [UNKNOWN]
presentation, which addresses the question, when do I need a noncontrast CT.
In the old days, patients were scanned often
with non contrast, Venus phase, and delayed phase.
Just everyone routinely imaged.
Now we really have to tailor our protocols.
We're concerned about radiation exposure, and we
have to think carefully about when we're going
to include specific acquisitions, and it has to
be indicated by the clinical question being asked.
So, when do I need a nonconstrast CT?
The answer: Not often.
It is no longer indicated for hepatic and pancreatic CT.
And let's talk about when we do need a noncontrast CT.
So, the indications include a patient who comes in to the ER with
acute chest pain and you're concerned
about an aortic dissection or aortic pathology.
This is specifically to identify an intramural hematoma, and
I'll show you a nice example in a minute.
Second indication, patients who are being imaged
following endoluminal stent placement, requiring noncontrast CT.
I will show you examples why this is part of that protocol as well.
The adrenal protocol includes a non-contrast
CT, the renal protocol in patients with
hematuria or who have a potential mass
that's being characterized require a non-contrast CT.
And as we all know, the renal stone protocol is simply a non-contrast CT.
So patient with acute chest pain in the E.R., we typically perform a
gated arterial phase if we're concerned about ascending aortic pathology.
And you really should perform a
precontrast scan to identify intramural hematoma.
An intramural hematoma is a, is a form of
pathology that has similar clinical implications as a dissection.
So if there's an intramural hematoma in the
ascending thoracic aorta, that patient may require emergent surgery.
This is something that you don't wanna miss.
If it's limited to the descending thoracic aorta then it is initially treated like a
Type B dissection depending on the configuration,
and the appearance, and the patient's clinical presentation.
So here's the next example of
a non-contrast CT showing an intramural hematoma.
You see the high density crescent along the wall, and as you can
see, the Hounsfield units measurements is in the range of 70 Hounsfield units.
Clearly there's an intramural hematoma.
Once you administer IV contrast, the density within
the aortic lumen makes it very hard to
determine whether that is intramural blood or just
some plaque along the wall of the aorta.
So, the non-contrast acquisition is essential.
Here's another patient with an intramural hematoma.
Just to show you the difference between the pre-constrast and the arterial phase.
On the precontrast we see the arrows, in
the ascending aorta showing the high density crescent, but
after you've given IB contrast it looks very similar
to just simple mural thrombus or some crescentic plaques.
Remember patients with acute chest pain in the ER gotta do a precontrast acquisition.
Patients who have had aortic stent and a luminal stent
placement need a noncontrast study as part of their protocol.
At Hopkins, we do a precontrast, an arterial phase and a venous phase.
The purpose of the precontrast scan
is to demonstrate calcification or surgical material
that, on an arterial phase, will look like an Endoleak or even a pseudoaneurysm.
So I'll show you a really nice example here of what we're looking for.
You see if you just had the arterial phase on
the right you might be concerned that that patient has
an endo leak within the aneurism sack but comparing to
the precontrast scan, we can see that this is just calcification.
So really essential in these patients to distinguish [UNKNOWN]
from calcification or surgical material is the non-contrast phase.
For the adrenal adenoma imaging for a patient with adrenal mass, and
you were trying to characterize whether it's an adenoma, we do a
pre-contrast acquisition, the reason being that most adrenal adenomas are lipid rich,
and they will have low attenuation, less than 10 on pre-contrast CT.
If it's less than 10, we know it's an adenoma, and we can stop imaging.
This is the cutoff that I use based on
a really good paper from the late 90s that showed
high sensitivity and specificity when the Hounsfield units are 10
on the pre-contrast study, I'm confident that that's an adenoma.
Some people will go a little bit higher with
their cutoff, but this is the one that I use.
And here's a really nice example of an adenoma measuring 0 Hansford Units.
This is because of the presence of microscopic fact.
If the Hansford Units are higher, and you're concerned
that it, or you're, you suspect that it may
be lipid pore adenoma, then we go on to
perform the wash out part of the adrenal protocol.
Okay, so I hope that helps.
The next topic that I will be presenting is, what am I missing on a noncontrast CT?
Thank you very much.