Diffusion Tensor Imaging


Posted on 29th March 2008 by Gordon Johnson in Uncategorized

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This series on Advances in Neuroimaging began with a quote from an article describing recent developments with Diffusion Tensor Imaging, or DTI. DTI is essentially a technique that allows us to see pathology in what are called fiber tracts within the white matter of the brain, even though individual axons are too small to be see without a microscope. If you have ever see the an insulation removed phone cable (as opposed to a telephone wire) you will see that inside the large cable, there are many small and colored
Smaller wires. This is analogous to the axon tracts within the white matter of the brain. Even though individual axons are microscopic, they tend to run in pathways with other axons, making a configuration that is large enough to image, with the right imaging method. That imaging method is DTI.

Within the brain, the water molecules tend to conglomerate and move, along the contours of the axon or fiber tracts. If you were to get a several pieces of string wet and then hold them vertically, you would probably see the water running down each strand. This is essentially what can be imaged in DTI. When diffuse axonal injury occurs in concentrated areas in the brain, even though we cannot see any of the individual axons that are damaged, we are able to see an interruption in the flow of water molecules along these fiber tracts. While DTI is certainly not showing all of the axonal damage throughout the brain, it is one more tool to show pathology, and in recent studies may be a strong indicator of those concussions which cause persisting and permanent deficits.

Tailored Protocols in Identifying Pathology in Post Concussion Syndrome


Posted on 28th March 2008 by Gordon Johnson in Uncategorized

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We began our series on “Advances in Neuroimaging” with first our blog on Increased Field Strength – and then yesterday’s blog on Dilated Perivascular spaces. Today, we will discuss the need for tailored protocols in properly investigating Mild Brain Injury and the existence of Post Concussion Syndrome, aka, Subtle Brain Injury.

The difference between a radiologist’s “call” of a normal or abnormal scan may also be dependent on the protocols that a given center is using. In a speech in 2002 I called for what I described as the forensically guided scan. Another more politically correct way to call it is a “tailored protocol or protocol for a specific condition.” When using a tailored protocol, you have a much greater probability of finding an abnormality related to the condition that you are specifically looking for. There can be no argument that a flexible approach to neuroimaging isn’t appropriate. If you find something, it is worth the effort. (Of course corporations and insurance companies will always whine about any extra money of effort to identify any pathology.)

If the radiologist is not directed to seek subtle pathology and applies the same techniques and level of inquiry that would be used in an acute setting where the search is for acute hemorrhage, the chances of a scan finding subtle yet significant pathology go down exponentially.

One of the areas where there may be a major advantage in a tailored protocol, is in the area of hemosidrin staining. Hemosidrin is the stain on brain tissue, left behind by blood that has now been reabsorbed back into the blood system. As an analogy, think of getting a glob of ketchup on a white shirt. When the ketchup first lands, it is clearly visible, has three dimensional mass and continues to spread. You quickly wipe it off, stop the spreading, but there is a bright red spot where the ketchup had been. You wash the shirt, the ketchup is all gone, but a stain remains. A bleed does the same thing to brain tissue. It at first has dimensional mass and will show up on a CT scan. Later, when stil fresh, it will likely show up on a conventional MRI. But as all of the significant mass of the blood has been reabsorbed, all that will be left is the stain. Neuropathologists have known this for generations, because they can see this stain on autopsy. Recent advances in MRI protocols, have created ways in which the magnet and the computer that inteprets the data, can identify this “hemosidrin” staining.

Again, an excerpt from a deposition of a leading neuroradiologist provides significant illumination:

1 Q. With respect to neurotrauma, what
2 typically would have a higher concentration of
3 iron in it?
4 A. Well, injuries — iron is basically
5 a by-product of blood. And when we look at
6 iron in the body, we usually see it when
7 it’s not in red blood cells or normal
8 structures. We usually think of it as
9 hemosiderin, which is sort of an iron stain,
10 basically.
11 So hemosiderin in trauma is what
12 you would look for after the acute phase.
13 If you have someone who is injured
14 immediately and is actively bleeding, or has
15 a lot of bleeding going on in the brain,
16 that’s a very different picture than the iron
17 that I’m talking about. The iron that I’m
18 talking about is leftover or by-product.
19 So after the fact, you had some
20 kind of bleeding in the brain, for whatever
21 reason, but a trauma you would be talking
22 about sometimes shearing injuries can bleed.
23 You can have contusions that will bleed.
24 Hematomas in the brain.
25 But when the blood is basically
1 gone, what’s left behind is a stain, a
2 hemosiderin stain. And that hemosiderin shows
3 up very black on MRI scans. Susceptibility
4 weighed sequences are designed to bring that
5 out.

Other areas where tailored protocols may come into play is increasing the proximity of the MRI slices thru the brain from the standard 2 mm slices to one mm. In essence, this improvement allows us to see pathology that might exist between the layers of the 2mm slices. Another potential advancement which is not getting much attention yet, is to increase the pixel size of the scan to 1024 by 768, (similar in size to the standard resolution of most laptops) from what is typically something more equivalent to 360 pixels by 240 (more the size of a typical Youtube video.) This type of resolution is now common when scanning for tumors. Why not brain injury? Partially priorities, but also because not enough thought is given as to where to aim this higher resolution. My suggestion is that they should be aimed: at the frontal lobes, particularly the underside of the frontal lobes, the lower brain structures and at the brain stem, areas that are difficult to image conventionally because the structures are small and the skull close by.

With all tailored protocols, there is always a cost benefit analysis. They cost more, require more attention from the neuroradiologist, and in some cases, can involve some loss of image sharpness. They may also extend the amount of time that the patient must stay in the scanner, which can be unpleasant and exceedingly boring. Faster scanning times are eliminating some of that disadvantage, but mostly these scans aren’t done, because no one demands it.

If you are having a scan done on someone with Post Concussion Symptoms, insist on at least the hemosidrin investigation, and hopefully the 1 mm slices. Someday, I believe that the 1024 x 768 resolution will be the norm, at least in the areas most likely susceptible to mild brain injury pathology.

Diffusion Tensor Imaging

Dilated Perivascular Spaces in Identifying Mild Brain Injury

1 comment

Posted on 26th March 2008 by Gordon Johnson in Uncategorized

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We began our series on “Advances in Neuroimaging” with yesterday’s blog on Increased Field Strength – the improvement from the 1.5 Tesla MRI’s to the 3 Tesla MRI’s. Today’s blog will discuss the evolving research that seemingly insignificant evidence of abnormalities on lower field strength scans, can illuminate evidence of traumatic injury. This is particularly true of what is technically called dilated perivascular spaces, also called Virchow Robbin Spaces. In essence, these are areas surrounding blood vessels in the brain, where myelin sheath or other brain tissue is missing, and thus show up as holes (white spots – also called UBO’s – unidentified bright objects) on the MRI scans. The technical term in an MRI report would be “areas of abnormal increased signal intensity.” Myelin sheath is the insulation type substance that protects the length of most multilevel axons in the brain.

Even though the 3T scans allow us to see these bright spots much clearer, this one term, “dilated perivascular spaces”, is still being used to describe lots of very different types of pathology. Again, excerpts from a recent deposition I conducted:

10 Q. We have the term called dilated
11 perivascular spaces that we’ve talked about.
12 Peri meaning?
13 A. Around the vessels. It’s the
14 spaces around blood vessels of the brain.
15 Q. And in a normal brain, what is in
16 those — why are there no spaces?
17 A. Well, there actually are spaces.
18 There’s spaces in everybody. It’s just that
19 they’re very, very small. And in some
20 patients you really see very few, or you
21 don’t really see hardly any, but they’re
22 there.
23 And then if they enlarge, because
24 you have lost substance in the brain around
25 them, then you refer to them as dilated
1 perivascular spaces, or enlarged spaces. And
2 what they fill in with is basically water;
3 cerebrospinal fluid is water.
4 Q. What type of brain matter is lost
5 in these, in the dilated perivascular
6 situation?
7 A. It’s basically a white matter
8 substance of the brain predominantly, because
9 that’s where you — that’s where these
10 perivascular spaces tend to be is mostly in
11 the white matter. So basically what you’ve
12 lost is some of the connecting fibers.
13 Q. Now, white matter is the axonal
14 part of the brain; is that fair?
15 A. Right. It’s the connecting fibers
16 of the brain. I made the analogy earlier of
17 the telephone systems. Telephone systems on
18 the surface of the brain, they’re basically
19 neurons. The connecting fibers are the
20 axons. And those connecting fibers are what
21 make up the white matter.
22 Q. And they call it white matter
23 because it’s white when you autopsy the
24 brain?
25 A. Depending on how you fix the
1 brain, yes.
2 Q. What is it that you’re seeing
3 that’s white? Is it the axons themselves or
4 the insulation around it?
5 A. It’s the insulation around them,
6 the myelins.
7 Q. And when we see dilated
8 perivascular spaces, are we seeing absence of
9 axons or absence of the insulation?
10 A. It could be both. We’re seeing an
11 absence of one or the other.
12 Q. Is the insulation considerably
13 larger in scale than the axons are?
14 A. Yes.
15 Q. Do you have any sense of the
16 magnitude of the difference?
17 A. An axon is on the order of about
18 50 microns. And then it has a mild sheath
19 around it. So that covering around that. So
20 the whole thing is really small.
21 Q. How small is a micron relative to
22 a millimeter?
23 A. It’s a thousandth of a millimeter.
24 Really tiny.
25 Q. So 50 microns would be 1/20th of a
1 millimeter?
2 A. Pretty small.
3 Q. Can you see axons in a human
4 macroscopically?
5 A. Only collections of them. Only
6 bundles of them. Large groups of them. You
7 can’t see 50 micron scales.
8 Q. And relative to the 3-Tessla MRI,
9 what is its resolution in terms of pathology
10 and the smallest pathology you see?
11 A. I think that depends on the type
12 of pathology. I would say in general you’re
13 in the 1 millimeter resolution range.
14 Depending on the pathology, you could go
15 smaller. Some pathology you might have to go
16 a little bigger. I feel very confident
17 calling 1 millimeter lesions.
18 Q. How many axons grouped together do
19 you think you would have to see to be able
20 to see it on the MRI?
21 A. Well, at the very least hundreds,
22 and probably thousands.
23 Q. Some are thicker than others?
24 A. Right.

For a more detailed explanation of the pathology of diffuse axonal injury, see http://subtlebraininjury.com/Neuropath

A dilated perivascular space on a 3T scan is no longer a vague bright dot but now has definition, measurable size and distinguishable shape. A neuroradiologist may be able to distinguish between such dilated spaces that can be caused by trauma, from other disease processes. .

25 Q. Is there weighting that goes into
1 your differential diagnosis when you look at
2 a dilated perivascular space in terms of more
3 likely trauma, more likely aging, more likely
4 microvascular? Is there — can you look at
5 the character in relation to the location of
6 perivascular spaces and shift a probability of
7 one diagnosis versus another?
10 THE WITNESS: Well, one of the
11 things that I’m looking at right now are
12 different types of perivascular spaces. And
13 we have a study that we’re conducting where
14 we’re looking at — I actually think there
15 are two types of perivascular spaces. There
16 are perivascular spaces that I would refer to
17 pathologic, and perivascular spaces that would
18 I would consider developmental.
19 So I’m going to eliminate the ones
20 that have — and what you’re asking me I’m
21 going to separate out the developmental ones.
22 The developmental ones, I think are
23 very round. They’re usually in the deep
24 basal ganglion region of the brain. They’re
25 very common. They can be extremely large.
1 They’ve been described in literature to be
2 well over a centimeter in size. Very big.
3 But I don’t think they ha ve any clinical
4 significance at all.
5 Then there are dilated perivascular
6 spaces that I think are pathologic, meaning
7 that something caused them, whether that is
8 aging, whether that is a disease process,
9 whether that’s trauma.
10 I think that differentiating
11 between those requires you to look at a
12 variety of factors. And that is, does the
13 patient have any other disease condition?
14 What is the age of the patient? What are
15 the size of these perivascular spaces relative
16 to the age of the patient? Are they greater
17 than you anticipate for that patient’s age?
18 Is the location predominately in areas of the
19 brain where those particular disease processes
20 are most common? Do they fit together in that
21 way?
22 So my opinion is that we probably
23 will be able to over time improve our
24 differential diagnosis. I think we can put
25 it into two categories right now. Andhttp://www.blogger.com/img/gl.link.gif then
1 I think beyond that it really requires
2 correlating it with clinical information, the
3 age, and the locatihttp://www.blogger.com/img/gl.link.gifon of the perivascular
4 spaces.

In summary, we have now covered improved field strength and dilated perivascular spaces. In tomorrow’s blog, we will address the need for tailored protocols in properly investigating Mild Brain Injury and the existence of Post Concussion Syndrome, aka, Subtle Brain Injury.

Advances in Neuroimaging


Posted on 25th March 2008 by Gordon Johnson in Uncategorized

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My topic for the rest of this week is advances in diagnosing brain injury thru improved neuroimaging. A recent study out of BYU, highlights some of the exciting changes that occurring, “New study shows brain changes from concussion
By Elaine Jarvik, Deseret Morning News Published: Monday, March 17, 2008.
See http://deseretnews.com/dn/view/0,5143,695262379,00.html

The Deseret article begins:

“Even after a severe concussion, a brain can look normal and healthy on a traditional brain scan. But now a study co-authored by a Brigham Young University psychology professor, using a new kind of MRI technique, reveals brain changes that are subtle but significant.”

This article is talking about a technology called DTI imaging, but to fully understand the advances in neuroimaging, it is necessary to understand some basics about the science of neuroimaging and improvements in both the magnets and the software to interpret the raw information has changed.

The last three years have been an exciting time to be a brain injury lawyer because the implementation of 3 Tesla MRI scanners for clinical diagnosis of mild brain injury has resulted in an exponential increase in the number of abnormal scans for our clients. But increased field strength is part of the equation.


Tesla is the measurement of the strength of a magnet. 1.5 Tesla (1.5 T) is the current prevalent maximum field strength of MRI scanners found in US hospitals, with many facilities having scanners with weaker field strengths. While research facilities have been using considerably stronger field strengths than the 1.5 for at least five years, it wasn’t until mid 2004, that 3 T MRI scanners began to appear for clinical use. As I write this in March of 2008, there is likely a 3T MRI scanner at most major university medical centers, although many of these may still be restricted to research only applications.

One way to conceptualize the improvement in scanners is to compare such to similar improvements in the mega pixel capacity of a digital camera. An 8 mega pixel camera has roughly twice the resolution of a 4 mega pixel camera, and while the difference in MRI scanners don’t quite track a pure arithmetic improvement, the analogy holds quite nicely. After all, MRI scanners are essentially cameras, that use as the contrast agent, the vibrations of magnetized protons, instead of light.

My examination of a leading neuroradiologist, will a bit technical, will assist those who want to understand the details of these new advances:

My examination of a leading neuroradiologist in a recent case, may be helpful to understand the basic principles:

23 Q. My understanding is that MRI
24 imaging essentially uses an especially powerful
25 magnet with respect to 3-T to make the
1 molecules inside the brain resonate; is that
2 correct?
3 A. Correct.
4 Q. Explain what’s really going on
5 there.
6 A. What happens with an MRI
7 examination — for example, you mentioned
8 specifically 3-T. Well, the T stands for
9 Tesla. The more — the higher the Tesla
10 number, the more power the magnet. Which
11 really translates to your ability to see
12 smaller things.
13 So in many ways it’s analogous to
14 a microscope. If you have a higher powered
15 microscope you can see things better than you
16 can a lower powered microscope. An MRI
17 scanner is a higher powered. An MRI scanner
18 you can see things — many things you can
19 see better.
20 It’s not absolutely universal that
21 you see everything better, but for the most
22 part you see things much better on a higher
23 field strength magnet.
24 No matter what field strength
25 magnet you’re in, if I put you in an MRI
1 machine, basically what happens is that the
2 protons, which are part of the water
3 molecule, tend to line up with a magnetic
4 field.
5 So right now your water molecules
6 and your protons are just random in the
7 direction. They have a direction, and that
8 direction is random all over the place.
9 When I put you in an MRI machine,
10 they all line up. They all line up with a
11 magnetic field. And then what we do is we
12 give a radio frequency pulse. And it’s
13 basically very, very similar to an FM radio
14 wave. It’s almost the same energy as an FM
15 radio wave.
16 And basically what we do is we hit
17 your body with what’s called a radio
18 frequency pulse, which is really similar to
19 an FM radio wave. So it’s not dangerous.
20 There’s nothing bad about it. But what it
21 does do is it knocks those protons out of
22 that alignment.
23 And then as those protons come
24 back into alignment, they come back into
25 alignment at different rates, different speeds
1 based on the tissue, which is referred to as
2 a relaxation time.
3 So that the time it takes for
4 those protons to come back into alignment is
5 different for the skin, for the bone, for the
6 skull, for the cerebrospinal fluid. They all
7 have different rates.
8 The computer then assigns a gray
9 scale. So it’s kind of like paint by numbers.
10 If the relaxation rate has a certain number,
11 then it gets a certain color.
12 So basically, the computer does
13 something that’s completely analogous to paint
14 by numbers, and creates a picture out of
15 that.
16 And we do that with different
17 settings, depending on what we’re looking for.
18 And we can emphasize different tissues.

Increased field strength is only part of the breakthrough in neuroimaging. As more and more pathology is seen on these scans, neuroradiologists are realizing that what were considered to be insignificant findings on lower field scans, are of the pattern and nature most likely explained by traumatic forces, not disease processes or normal variants.

Dilated Perivascular Spaces in Identifying Mild Brain Injury