0:00

The third group of sequences that we utilize

0:03

in evaluating liver lesions are the T1

0:06

weighted in and out of phase sequences.

0:08

These are performed without intravenous

0:10

contrast and performed without fat saturation.

0:14

So here we can see the T1 out of phase

0:16

sequence and the in-phase sequence.

0:18

These are gradient echo sequences

0:20

performed with breath holds.

0:22

The in-phase sequence is obtained at an echo time,

0:25

at which fat and water protons are aligned with one

0:28

another, while the out-of-phase sequence are obtained

0:31

at an echo time where fat and water oppose one another.

0:33

From a practical perspective, this means that

0:35

anywhere where you have a fat and water interface,

0:38

such as the edge of the liver with the adjacent

0:39

fat, you're going to see this very, very dark line.

0:42

And this is known as the India ink artifact.

0:44

So what do we use these sequences for?

0:46

Well, we use it to detect the presence of hepatic

0:49

steatosis, and this is identified as a loss of signal

0:53

within the liver parenchyma on the

0:56

out-of-phase sequence versus the in-phase sequence.

1:00

We can use the spleen or potentially the

1:02

paraspinal muscles as an internal control.

1:05

The latter two organs should not lose

1:07

signal on the out-of-phase sequence.

1:09

The in-phase sequences, because they're obtained

1:11

at a longer echo time, will show increased

1:13

susceptibility artifact associated with any

1:17

eclipse, any metallic deposition, and even gas.

1:20

So if you're looking for gas within a liver lesion,

1:23

you're going to look at the in-phase sequence for that.

1:25

These sequences can also be used to detect the presence

1:28

of hyperintense T1 signal within any liver lesions,

1:32

though this is better detected on the isotropic fat

1:35

suppressed sequences, which we'll talk about next.