0:00

The post-contrast, T1-weighted,

0:03

fat-saturated images are performed using the

0:05

same parameters as the pre-contrast image.

0:08

However, we do these at three different time points, which

0:10

takes into account the dual blood supply to the liver.

0:13

The liver gets about 75 percent of its blood supply from the

0:16

portal vein and about 25 percent from the hepatic artery.

0:20

Now, the timing can be performed using a fixed delay or an

0:23

individual delay utilizing a test bolus or bolus tracking.

0:27

Here we have the first phase that we get,

0:29

which is often known as a late arterial phase.

0:32

We obtain this approximately about 30 seconds

0:34

after intravenous injection of contrast.

0:37

And you know you have a good late arterial phase

0:40

images if you see enhancement of the hepatic

0:42

artery over here as well as early enhancement

0:46

of the portal vein that you can see over here.

0:49

This is a very important sequence to get

0:51

right because it allows stratification of

0:54

liver lesions into one of four categories:

0:56

whether they're hypervascular or enhanced very

1:00

avidly early on, whether they're isovascular,

1:03

whether they're hypovascular, or avascular.

1:07

The next phase is the portal venous phase.

1:09

This is obtained at about 70

1:10

seconds after injecting contrast.

1:13

And in this one you're going to see very homogeneous

1:15

opacification of the liver, as well as opacification

1:18

of all the vessels in the liver, including the

1:20

portal veins over here, as well as the hepatic veins,

1:23

the right hepatic vein, the middle hepatic vein,

1:25

and the left hepatic vein.

1:27

The final phase that we get is known as a

1:29

delayed equilibrium or interstitial phase.

1:32

You'll see it used differently

1:34

depending on who's talking about it.

1:36

And we typically obtain these at about

1:38

three minutes after intravenous injection.

1:40

Now depending on the case, we may obtain a

1:42

fourth post-contrast image at about ten minutes.

1:45

This is typically used if you're suspecting a

1:47

malignant liver lesion called a cholangiocarcinoma.

1:51

And if you're using an agent with partial

1:52

hepatobiliary excretion, we're going to

1:53

obtain a final phase at about twenty minutes.

1:56

As we go through the cases today, we'll

1:58

certainly come across cases where we

1:59

utilize that twenty minutes delayed phase.