Interactive Transcript
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So the next thing I wanted to
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discuss is kinetic curve assessment.
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And this is referring to what happens
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to the contrast as it enters a lesion
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or an area of tissue over time.
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And we consider abnormal enhancement to
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be enhancement of higher signal intensity
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compared to the background enhancement.
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on a contrast-enhanced scan.
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And, you know, as we saw from our examples
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of background parenchymal enhancement,
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sometimes it can be a little difficult
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to sort out what represents background
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and what actually represents an enhancing
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focus mass or non-mass enhancement.
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But we're going to evaluate our enhancement
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on the first post-contrast scan.
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And then we evaluate at multiple time points.
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Because in our protocol, we take three
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time points after contrast is administered,
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and then we can use those time points to
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create a curve and we look at the uptake of
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contrast and then the washout of contrast
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in tissues after contrast injection.
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So the rate of contrast uptake and
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washout depends on perfusion of the
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tissue, capillary permeability, the blood
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volume, the contrast media distribution
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volume, and local anatomy and physiology.
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And tumors often have highly permeable
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vasculature and rapid blood flow, so they
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tend to enhance earlier and more significantly
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than the surrounding breast tissue.
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And malignant lesions tend to have rapid
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initial enhancement and delayed washout.
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And benign lesions tend to have slow
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initial enhancement and progressively
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increasing enhancement over time.
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Unfortunately, it's not that easy, and
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there's a lot of overlap between the two.
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So when we look at kinetic curves, we're going
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to look at the initial phase, which is the
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first two minutes after injecting contrast.
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And contrast enhancement can be slow, medium, or
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fast, depending on how quickly that curve rises.
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And then the delayed phase,
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which is after two minutes.
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Is called either persistent plateau or
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washout, and persistent is going to be an
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increase in signal over time. Plateau will
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be no change in signal over time, and washout
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will be more than a 10 percent decrease
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in signal over time in that delayed phase.
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So just to show that graphically.
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This is what the enhancement curve looks like
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so our x-axis is time after injection, and
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our signal intensity is along the y-axis.
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So in that initial phase, the first two
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minutes, we can have slow enhancement,
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medium enhancement, or fast enhancement.
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And then the delayed phase can either be
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that type one or persistent enhancement where
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the enhancement continues to rise over time.
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Plateau or type two, which is that sort of flat
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curve, and type three or washout, which is the
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contrast is decreasing over time at that point.
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So the delayed phase is kind of important, and
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type one curve, as we said, was persistent,
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that continuous increase in signal over time.
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Type two is the plateau or flat curve, and type
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three is washout, which is an initial increase
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followed by a decrease in contrast enhancement.
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What we're trying to do, you know, this is in
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the ideal world, our malignant lesion would
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have this type of curve shown in red here.
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And basically rapid, rapid initial enhancement
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and then a washout over time, whereas a benign
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lesion might have a slow initial phase followed
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by persistently increasing signal over time.
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Eventually, benign and malignant might
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cross, but they're, that's pretty far out.
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And what we're trying to exploit
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with MRI is the difference between
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this peak for malignant lesions.
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And this lower level
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enhancement for benign lesions.
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So that there's that contrast difference.
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So on our early post-contrast phase images, our
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first sequence after contrast administration,
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that's when we have the best chance to pick
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up the difference between this malignant type
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curve and this benign type curve. Unfortunately,
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because there's overlap between the way
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the benign and malignant areas enhance, we
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can't, we can't always tell the difference,
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but you know, that's the general idea that
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you're, you're trying to exploit this, this
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space in the early post-contrast phase.
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So to show you some examples of what kinetic
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curves look like, this is a patient who has
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some non-mass enhancement in the right breast.
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And we've put a cursor over this
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area, and we have a color map.
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So most of our kinetic software—there are
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a variety of different vendors for this—but
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they'll do a color overlay of the entire image.
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And if you put a cursor over an area of
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interest, then you'll generate a curve
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based on the area indicated by that cursor.
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So for this portion of tissue that's
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indicated here, we have this time-intensity
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curve, which shows rapid initial rise and
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then persistently increasing over time.
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So this is a persistent delayed kinetics, and
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this is rapid initial enhancement, but this
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in general is a persistent curve and in.
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A lot of the kinetic software
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packages will colorize this type
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of curve as blue for persistent.
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The next type of curve is plateau.
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So we can see here, there's a mass here in the
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left breast.
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There are actually several masses in the left
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breast, but this one colorizes green, which
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is for plateau with this type of software.
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And when we put a cursor over it, we see
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that there's a rapid initial rise, and
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then the delayed phase is relatively flat.
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So this is a plateau-type curve.
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The third type is washout, and showing my
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cursor over an interpectoral lymph node.
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here, which is colorized as red.
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And when you put a cursor over
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it, this is the resulting curve.
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So we see a rapid initial rise
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and then a fall or decrease in the
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contrast enhancement over time.
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So this is the washout-type curve.
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And to evaluate kinetics, we
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use a kinetic software package.
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We see a color overlay of the entire
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breasts that we can scroll through, and
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then if there's a certain lesion that's
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of interest to us—a focus or a mass or an
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area of non-mass enhancement—we can move
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a cursor over it and generate that time
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intensity curve and take a look at that.
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And keep in mind that initially we thought
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kinetics would be very important, but over
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time what's been found is that morphology
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is usually more important than kinetics.
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And as spatial resolution has improved over
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the last few decades in MR technology,
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we can really see morphology
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even down to the size of small foci.
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So usually morphology is going to
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trump kinetics for most cases.
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