0:01

I would be remiss as a University of Pennsylvania

0:05

Neuroradiology fellow graduate if I didn't go through the

0:09

signal intensity characteristics of

0:12

intraparenchymal hematomas on MRI.

0:14

This was work that was done in the late 1980s and

0:18

early 1990s by a series of neuroradiologists,

0:23

including Bob Grossman, John Gamori, Scott Atlas,

0:28

Bob Zimmerman and David Hackney.

0:31

These were my mentors as I was a fellow,

0:35

and they went through the signal intensity characteristics

0:38

of hematoma based on the chemistry.

0:40

I'd like to share that with you.

0:43

The two concepts that you have to understand in order

0:46

to be able to analyze a hematoma on MRI

0:51

are proton relaxation enhancement,

0:53

which we usually refer to as pre, PRE.

0:56

And proton-electron dipole-dipole interaction.

1:01

Proton relaxation enhancement is due to the inhomogeneous

1:05

magnetic field that hematomas cause.

1:09

And this is usually due to T2 shortening effects,

1:13

secondary to concentration of charge within

1:17

a cell versus outside a cell.

1:20

And this will be the major factor

1:22

accounting for T2 shortening,

1:24

which means dark signal on a T2-weighted scan with

1:27

deoxyhemoglobin, that marker of acute hemorrhage,

1:31

and hemosiderin, that marker of chronic hemorrhage.

1:35

This is field strength-dependent, and therefore the dark

1:38

signal intensity on T2-weighted scan will vary depending

1:42

upon whether you're at low field strength.

1:43

For example, 0.15 tesla versus three tesla,

1:47

where it will be very dramatic.

1:49

The second concept I mentioned

1:52

was proton-electron dipole-dipole interaction.

1:55

We use the term "PEDDI" for this.

1:58

PEDDI refers to a T1 shortening effect

2:02

that occurs secondary to

2:04

the methemoglobin molecule's affinity for water.

2:07

The water molecule is able to approach the methemoglobin

2:11

molecule, and it leads to T1 shortening of water

2:15

protons in proximity to the methemoglobin molecule.

2:20

T1 shortening leads to bright signal

2:23

intensity on a T1-weighted scan.

2:26

And this is a field strength-independent property.

2:30

Let's look at the various components of

2:33

hematomas over the course of time.

2:36

The acute hematoma is dominated by deoxyhemoglobin.

2:40

This is an intracellular compound that leads to proton

2:45

relaxation enhancement and T2 shortening.

2:49

It is therefore field strength-dependent and will be very

2:51

dramatic as you go to gradient echo scanning or

2:55

susceptibility-weighted scanning.

2:57

Deoxyhemoglobin,

2:58

because it's a mark of acute hematoma

3:01

is often associated with bright signal intensity

3:05

around the hematoma,

3:07

secondary to the edema in the acute phase.

3:10

So what one has is an intact red blood cell

3:13

that has deoxyhemoglobin within it

3:16

and no deoxyhemoglobin outside the red blood cell,

3:20

which leads to a bar magnet effect

3:24

causing T2 shortening and dark signal on a T2-weighted scan,

3:28

and it usually occurs from 6 hours to three

3:31

days after the initial insult.

3:33

These are pulse sequences and CT scan showing

3:38

acute hematoma and deoxyhemoglobin.

3:42

The acute hematoma is bright on the CT scans,

3:47

hyperdense because of the globin content,

3:50

not the iron content but the globin or hemoglobin content.

3:54

On a T1-weighted scan,

3:55

and I'm showing this

3:57

is a T1-weighted time of flight MRA.

4:01

You see that the signal intensity of the acute hemorrhage

4:05

is isointense to low intensity on T1-weighted scanning.

4:10

This is fast spin echo T2-weighted scanning.

4:14

The fast spin echo scan shows dark signal intensity from

4:19

deoxyhemoglobin and proton relaxation enhancement,

4:24

T2 shortening effect.

4:26

This is the FLAIR scan.

4:30

And this FLAIR scan shows the same thing,

4:33

dark signal intensity, because it has T2 weighting

4:36

within the FLAIR scan.

4:38

This is your DWI scan.

4:40

And the DWI scan also shows dark signal intensity

4:45

because it has T2 weighting.

4:46

This is the ADC map showing dark signal intensity

4:50

but not due to cytotoxic edema,

4:52

but dark due to the presence of hemorrhage.

4:56

This is an SWI scan, a susceptibility-weighted scan.

4:59

As I said,

5:01

susceptibility-weighted imaging shows greater sensitivity

5:04

to blood products than fast spin echo.

5:07

And we could see that by the blooming effect and the size

5:10

of the hematoma between the T2 fast spin echo scan

5:14

versus the susceptibility-weighted scan.

5:15

You could see just how dark this is,

5:18

almost as dark as the bone

5:19

on the susceptibility-weighted image.

5:22

And finally, we have a post-gad T1-weighted scan.

5:26

And as you see,

5:28

the deoxyhemoglobin,

5:29

the acute hemorrhage is somewhat

5:31

low on T1-weighted imaging.