MRI versus CT Scanning
Dr. Zoran Rumboldt - Radiology
Host: Dr. Linda Austin – Psychiatry
Linda Austin: I’m Dr. Linda Austin. I’m interviewing Dr. Zoran Rumboldt, who is
Associate Professor of Radiology and Chief of Neuroradiology here, at the
Medical University of South Carolina.
Dr. Rumboldt, let’s talk about neuroradiology. Many patients get sent for a CAT scan or an
MRI (magnetic resonance imaging) of the brain.
Can you explain what the difference is between those two procedures,
what you’re looking for and why a doctor might order one versus the other?
Zoran Rumboldt: Well, there is a
fundamental difference in how these images are acquired. CT or CAT scan uses x-rays and a computer to
create images, so it’s more similar to, say, traditional radiological imaging
modalities, whereas MR uses magnetic properties of tissues to create
images. There are, then, differences in
what these different modalities offer in terms of diagnostic quality.
speaking, especially if you’re talking about the brain, MR is clearly the best
modality. However, MR may not be
available 24/7. Some patients may not
tolerate MRI because they can take half an hour, maybe even more. Some patients get claustrophobic. And, also, some patients may have cardiac
pacemakers, or some other devices, which are essentially contraindicated for an
MRI scan or, possibly, some patients may be in intensive care units, with all
the devices attached.
Linda Austin: Is it fair to say, also,
that a patient may not need the MR? For
example, when I think of patients coming into the emergency room after mild
head trauma, they seem to often get CT scans rather than MR scans.
Zoran Rumboldt: Sure. For trauma, certainly, CT is the modality of
choice, at least initially. MRI may help
detect some lesions that are not seen on CT.
But, in terms of patient management, it doesn’t really change it. Finding those lesions does not really affect
treatment, at that point. We don’t know
what we would do differently. CT is
great for finding those abnormalities that require immediate attention, such as
subdural hematomas, or other space-occupying lesions, that are life-threatening
and should be treated immediately.
Linda Austin: So, MR, then, gives you a
much more delicate, refined, detailed picture of soft tissues, correct?
Zoran Rumboldt: That is generally
correct. For instance, patients with
multiple sclerosis, brain tumors, or most intracranial abnormalities are
generally better served with MR.
However, for a number clinical situations, such as trauma, for instance,
CT is more than sufficient. And, since
it’s very fast and readily available, it is the preferred modality. It’s also cheaper. There are certain indications where CT,
actually, may be preferred over MR, for instance, say, evaluation of the
temporal bone. So, for patients with
problems with hearing, perhaps, especially if it’s the middle ear, it’s usually
better visualized with CT.
CT has made significant progress with more physiologic imaging, which was
pretty much reserved only for MRI, that is, CT perfusion and CT
angiography. So, for instance, nowadays,
patients that have a high suspicion of acute infarct, of stroke, would
typically get CT anyhow because, most of the time, that’s the first modality,
although a lot of studies that are published in journals are done with MRI. But, that does not necessarily reflect
real-life situations. So, those patients
get head CT, which is frequently negative.
But, now, we can offer something in addition to that. We’ve been doing that for a number of years
now. We do CT perfusion, which can
detect deficits in the blood supply to the brain, before you see the
abnormality on just plain CT scan.
look at certain mismatches and different aspects of the perfusion. And, we believe that, based on that, we could
tell if the tissue is salvageable or not, or what portion of that tissue may be
salvageable, which, then, can potentially guide treatment. If you don’t have salvageable tissue, you’re
just risking hemorrhage from TPA and other agents that are used to resolve
Linda Austin: I see. Let’s talk a little bit about MRI. Just how detailed is it? I’m sure that there are patients, for
example, who go for imaging because somebody’s concerned about a brain metastasis. How tiny of a lesion can you actually see?
Zoran Rumboldt: Again, it does depend on
how we perform MR imaging. MRI is very
versatile and has a number of different, what we call, sequences. For instance, when you acquire a CT image,
you can change the parameters a little, but it’s essentially always the same
kind of image. With MRI, we routinely do
at least five different things. We get
T1 weighted images, T2 weighted images, flair,
diffusion, and give contrast. So, all
these evaluate the brain, or other tissues, in a different fashion, and each
one of them provides additional information.
each one of those sequences gives us very high spatial resolution, typically,
within a very small area, such as the pituitary gland or, maybe, if we’re
looking for a source of seizures in the part of the brain known as the hippocampus,
or some other part, we can do that. We
can do very high resolution imaging of the entire brain as well, but it takes a
long time. There’s always this sort of
conflict between time and resolution in MR.
The higher the resolution you want to get, the longer it takes to
acquire them. Now, the longer it takes,
it becomes impractical, not just because you cannot keep people there forever,
but also because the people there start to move, so you actually lose image
quality. So, unless you have them under
general anesthesia, it may complicate things further.
Linda Austin: So, it’s a tradeoff?
Zoran: So, it’s a tradeoff. It’s sort of a continuous battle.
Linda Austin: Let’s talk about these
techniques from the patient’s point of view.
I hear a lot of patients talk about worrying about being claustrophobic
in the course of the procedure. You just
mentioned the difficulty with patients starting to move. Can you describe the experience for both CT
Zoran Rumboldt: I think very few
patients would be claustrophobic for a CT scan.
That’s, basically, for two reasons.
One: the gantry, the bore, is very short and fairly wide. So, you do not really have that experience of
being in an enclosed space. At the same
time, the exams are fairly short, a matter of a few minutes.
MR, typically, those bores are longer and narrower, and the exams take, I’d
say, at least 10 minutes and, frequently, over half an hour. So, that would increase your chance of
becoming claustrophobic. Now, having
said that, there are new scanners, and we will be acquiring one in a few
months, that have these wide bores, so they’re getting very close to CT in that
respect. They’re frequently called an
Open Bore, although they’re not fully open.
They just have more space and patients tend to tolerate them much
Linda Austin: Dr. Rumboldt, I know one
of the things patients worry a lot about is just tolerating these
procedures. We talked a few minutes ago
about CT scan not being difficult to tolerate.
How about MRI? What makes that
difficult, and can patients get medication or something to calm them down if
that’s a problem?
Zoran Rumboldt: It’s certainly going to
depend on the patient. A lot of patients
have no problems, whatsoever. We do
provide medications to help them cope with it and, in some cases, it is
necessary, especially in children, I should say. There’s a substantial portion of children, 2
to 10 years of age, who require general anesthesia.
Linda Austin: Thank you so much for
talking with us today.
Zoran Rumboldt: Sure. You’re welcome.
Linda Austin: Bye.
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