0:01

So the next thing I wanted to

0:02

discuss is kinetic curve assessment.

0:06

And this is referring to what happens

0:09

to the contrast as it enters a lesion

0:13

or an area of tissue over time.

0:15

And we consider abnormal enhancement to

0:18

be enhancement of higher signal intensity

0:21

compared to the background enhancement.

0:23

on a contrast-enhanced scan.

0:26

And, you know, as we saw from our examples

0:28

of background parenchymal enhancement,

0:29

sometimes it can be a little difficult

0:31

to sort out what represents background

0:34

and what actually represents an enhancing

0:38

focus mass or non-mass enhancement.

0:42

But we're going to evaluate our enhancement

0:45

on the first post-contrast scan.

0:48

And then we evaluate at multiple time points.

0:52

Because in our protocol, we take three

0:55

time points after contrast is administered,

0:58

and then we can use those time points to

1:01

create a curve and we look at the uptake of

1:06

contrast and then the washout of contrast

1:08

in tissues after contrast injection.

1:12

So the rate of contrast uptake and

1:14

washout depends on perfusion of the

1:17

tissue, capillary permeability, the blood

1:20

volume, the contrast media distribution

1:23

volume, and local anatomy and physiology.

1:27

And tumors often have highly permeable

1:29

vasculature and rapid blood flow, so they

1:33

tend to enhance earlier and more significantly

1:37

than the surrounding breast tissue.

1:40

And malignant lesions tend to have rapid

1:43

initial enhancement and delayed washout.

1:46

And benign lesions tend to have slow

1:48

initial enhancement and progressively

1:51

increasing enhancement over time.

1:53

Unfortunately, it's not that easy, and

1:56

there's a lot of overlap between the two.

2:00

So when we look at kinetic curves, we're going

2:02

to look at the initial phase, which is the

2:04

first two minutes after injecting contrast.

2:08

And contrast enhancement can be slow, medium, or

2:11

fast, depending on how quickly that curve rises.

2:15

And then the delayed phase,

2:17

which is after two minutes.

2:19

Is called either persistent plateau or

2:22

washout, and persistent is going to be an

2:25

increase in signal over time. Plateau will

2:27

be no change in signal over time, and washout

2:30

will be more than a 10 percent decrease

2:33

in signal over time in that delayed phase.

2:36

So just to show that graphically.

2:38

This is what the enhancement curve looks like

2:42

so our x-axis is time after injection, and

2:46

our signal intensity is along the y-axis.

2:49

So in that initial phase, the first two

2:51

minutes, we can have slow enhancement,

2:56

medium enhancement, or fast enhancement.

2:59

And then the delayed phase can either be

3:01

that type one or persistent enhancement where

3:03

the enhancement continues to rise over time.

3:07

Plateau or type two, which is that sort of flat

3:11

curve, and type three or washout, which is the

3:14

contrast is decreasing over time at that point.

3:19

So the delayed phase is kind of important, and

3:24

type one curve, as we said, was persistent,

3:26

that continuous increase in signal over time.

3:30

Type two is the plateau or flat curve, and type

3:33

three is washout, which is an initial increase

3:37

followed by a decrease in contrast enhancement.

3:42

What we're trying to do, you know, this is in

3:44

the ideal world, our malignant lesion would

3:47

have this type of curve shown in red here.

3:52

And basically rapid, rapid initial enhancement

3:55

and then a washout over time, whereas a benign

3:59

lesion might have a slow initial phase followed

4:04

by persistently increasing signal over time.

4:07

Eventually, benign and malignant might

4:09

cross, but they're, that's pretty far out.

4:13

And what we're trying to exploit

4:15

with MRI is the difference between

4:18

this peak for malignant lesions.

4:21

And this lower level

4:23

enhancement for benign lesions.

4:25

So that there's that contrast difference.

4:27

So on our early post-contrast phase images, our

4:31

first sequence after contrast administration,

4:34

that's when we have the best chance to pick

4:37

up the difference between this malignant type

4:40

curve and this benign type curve. Unfortunately,

4:43

because there's overlap between the way

4:45

the benign and malignant areas enhance, we

4:48

can't, we can't always tell the difference,

4:51

but you know, that's the general idea that

4:53

you're, you're trying to exploit this, this

4:56

space in the early post-contrast phase.

5:00

So to show you some examples of what kinetic

5:03

curves look like, this is a patient who has

5:07

some non-mass enhancement in the right breast.

5:11

And we've put a cursor over this

5:13

area, and we have a color map.

5:15

So most of our kinetic software—there are

5:18

a variety of different vendors for this—but

5:21

they'll do a color overlay of the entire image.

5:25

And if you put a cursor over an area of

5:27

interest, then you'll generate a curve

5:29

based on the area indicated by that cursor.

5:33

So for this portion of tissue that's

5:35

indicated here, we have this time-intensity

5:37

curve, which shows rapid initial rise and

5:41

then persistently increasing over time.

5:44

So this is a persistent delayed kinetics, and

5:47

this is rapid initial enhancement, but this

5:50

in general is a persistent curve and in.

5:53

A lot of the kinetic software

5:55

packages will colorize this type

5:58

of curve as blue for persistent.

6:03

The next type of curve is plateau.

6:06

So we can see here, there's a mass here in the

6:09

left breast.

6:10

There are actually several masses in the left

6:12

breast, but this one colorizes green, which

6:16

is for plateau with this type of software.

6:19

And when we put a cursor over it, we see

6:21

that there's a rapid initial rise, and

6:25

then the delayed phase is relatively flat.

6:27

So this is a plateau-type curve.

6:31

The third type is washout, and showing my

6:36

cursor over an interpectoral lymph node.

6:41

here, which is colorized as red.

6:43

And when you put a cursor over

6:45

it, this is the resulting curve.

6:47

So we see a rapid initial rise

6:49

and then a fall or decrease in the

6:52

contrast enhancement over time.

6:54

So this is the washout-type curve.

6:57

And to evaluate kinetics, we

6:59

use a kinetic software package.

7:03

We see a color overlay of the entire

7:06

breasts that we can scroll through, and

7:09

then if there's a certain lesion that's

7:11

of interest to us—a focus or a mass or an

7:14

area of non-mass enhancement—we can move

7:16

a cursor over it and generate that time

7:19

intensity curve and take a look at that.

7:22

And keep in mind that initially we thought

7:25

kinetics would be very important, but over

7:27

time what's been found is that morphology

7:30

is usually more important than kinetics.

7:32

And as spatial resolution has improved over

7:37

the last few decades in MR technology,

7:39

we can really see morphology

7:43

even down to the size of small foci.

7:48

So usually morphology is going to

7:51

trump kinetics for most cases.