New and Potential Clinical Applications of Microbubble Sonography

Opening Remarks and Dedication

I have no relevant financial relationships to disclose,
but I might have three others that are not financial.

If you look at this picture, I'm really not an astronaut,
though it is hard to believe, I think.

But some people call me spacey at times,
but my first name really is not Kevin either.

And this presentation I wanna dedicate in memory
of my mother,
because she always encouraged me to think big.

And here's John ALD Kennedy describing his wish that the country be dedicated.

As he said, we choose to go to the moon in this decade
and do the other things, not because they are easy, but
because they were, they're hard.

And I think I put the challenge to everyone to think big.

My mother would've done that too.

Objectives

Objectives, both the diagnostic
and therapeutic applications of microbubbles.

First, diagnostic part to look at tumor response,
to use ultrasound as molecular imaging to label
microbubbles to go to particular areas,
to decrease collateral damage, for example,
for oncologic treatment therapy.

The microbubble can be used for therapy
and delivery of drugs through sono porion.

And I will talk about this enhanced treatment of,
for example, Alzheimer's
or brain tumors that normally there's a blood-brain barrier,
which works very effectively.

The microbubbles can be used to improve drug delivery,
and this is very exciting.

I wanna also familiarize you with a new term,
theranostics, which is a combination of diagnostics
and therapy because the border between
diagnosis and therapy now is being blurred.

So this is a new term. As I said.

I'll talk about tumor response assessment with microbubbles
labeled microbubbles and therapeutic applications.

Research Support

This is my research support.

Thus far I'm very appreciative of
several NIH grants, several grants from the A IUM,
discovery grants.

I'm appreciative of Philips
healthcare helping us out,
and Broco and lenius.

Tumor Angiogenesis Concepts

Okay, firstly, let's
Get some concepts down concerning tumor angiogenesis.

The picture on the left is an scanning electron micrograph
of a few millimeter breast tumor.

And as you can see, this breast tumor
has multiple tiny vessels surrounding it.

And it's the theory of Dr.
Judith Folkman that in order for tumors to grow from
maybe a few millimeters to a centimeter
or so, they have to incite a new blood supply
neo angiogenesis.

And they do this through what's called
Vasogenic Endothelial Growth Factor vegf.

And what it produces is a tumor
that has actually very irregular central blood flow.

There's areas of necrosis that occur very early on,
and we know that tumors have increased interstitial pressure
because they don't have the typical ordered lymphatics
that normal tissue has.

Now, if we look at the vessel process in tumor angiogenesis, again,
I've referenced a beautiful article
with these diagrams.

What happens first is that there's fenestration
of the basement membrane surrounding the small capillary endothelial cell.

And then the fibroblasts come through this endothelial
cell gap, and they set up a scaffold for
neo vessels that eventually are made patent in the center of the vessel.

And thus, there is new blood supply to the tumor.

This is a comparative scanning electron micrograph
from Peter Choi and his colleagues at the NIH.

On the left, we see an artery going to an arterial,
going to a capillary, going to a small venous
structure, going to a venial.

And this is very organized hierarchy of vessels.

On the right is a comparable scanning electron micrograph
of a tumor.

And as you can see, hopefully the new blood vessels
are very irregular in their caliber,
very clustered, very abnormal.

And if you're a red blood cell, just like going
down a highway, you have an interstate going
to a smaller road, going to a back road, et cetera,
very organized here.

If you're a red blood cell, you just have a whole bunch
of blind ending crazy network of vessels.

And of course, at least I think this indicates why we see
increased washout phase, at least in some
of the tumors that we see and have studied.

This is a beautiful diagram from Scientific American,
an article written by Dr.
Jane from Harvard, who is an expert on tumor angiogenesis.

And I wanna make a few pertinent comments.

So, diagrammatically, here's the tumor,
and here the blood vessels supplying this tumor,
but tumors produce these tiny irregular
blind ending, chaotic appearing vessels.

Well, why is this important?

Well, because in order to get the best chemotherapy and
trying to understand how
to best treat lesions, we can understand that all these
abnormal vessels, the concept of these abnormal vessels have
to be taken care of.

And perhaps if we get rid of these vessels,
we have a more efficient way of treating the tumor.

Again, microscopically tumor vessels are leaky,
as shown in this diagram.

They're very irregular.

They're not hierarchical in nature.

So the tumor microenvironment,
we have dysfunctional vessels, which I've described,
produce conditions of low oxygen, hypoxia,
and high acidity.

Well, why is this important?

Because the ability to treat tumors, for example,
in radiation, is related to their hypoxic
or non hypoxic state.

Radiation in certain chemotherapies that require oxygen
to kill are ineffective in tumors.

This is important. Immune cells
that might attack cancer cells cannot
function in an acidic environment in the tumor
without oxygen.

Hypoxia causes changes to gene activity
and promotes tumor cell migration
in healthy tissues.

The fluid backup tumors, tissue swells,
and this is shown in the clinical world
as lymphedema, for example, causing painful symptoms.

Fluid pressure drives tumor generated proteins
and cells toward healthy tissues into lymphatic vessels,
increasing the chance of metastases.

So if we kind of understand what is shown in this diagram,
I think we understand a little bit about tumors
and how to not only diagnose them,
but potentially treat them.

Microbubbles Introduction

This is just a
Funny slide.

Dr.
Michelle Robin, who is chief of ultrasound in Birmingham,
three hours south of Nashville.

And I were walking at the World Federation meeting in
Seoul, Korea in 2006.

And we came across this
and I said to my wife, I said,
this looks like macro bubbles.

We had just gotten outta session
concerning microbubbles.

So, what we're interested in microbubbles, these are small structures, about a third
the size of a red blood cell.

Here's the animation showing a capillary.

And the blue balls are conceptually a microbubble.

Now, when we look at a slab of tissue,
it would take a hundred vessels with blood flow to get a adequate doppler signal.

But really in cancer, the
action is at the capillary level, not at the larger vessel.

So that if we could calculate the true perfusion defined
as blood flow in ML per second over a particular volume,
we could actually understand tumor dynamics a lot better.

And when we look at the equation,
which I'll show you in a minute, for perfusion,
there's an alpha and a beta.

Well, by understanding what we're seeing with microbubble profusion,
we can actually calculate these two parameters
and thus come up with a estimation,
a very close estimation, relative estimation of perfusion.

Microbubble Properties

Okay, the microbubbles are small.

They're made up of a central gas surrounded
by a lipid shell.

And their diameter is one, is two to 15 microns.

Understanding a red blood cell is about seven microns.

And when exposed to ultrasound,
they resonate, they oscillate.

They, as you can see here from this diagram,
they can go from five microns to 50 microns in their oscillation.

It's this oscillation that produces a harmonic
that allows us to image them relative
to surrounding echoes.

So our signal over noise is much better
because these microbubbles can be imaged
with harm harmonics.

This is a picture of the definitive microbubbles.

And as you can see, they're pretty homogeneous in size.

And you can see them compared to the micro,
to the scale at the bottom, which is five microns.

Now, this is a picture courtesy of Dr.
Caskey and his colleagues at uc Davis.

And this is a picture, kind of a animation, kind
of a neat animation of
the microbubble oscillating, and then breaking.

Perfusion Estimation with Microbubbles

So to estimate profusion, as I mentioned, this is the formula that we're looking at the alpha and the beta.

Now, to do accurate assessment of profusion,
one has to get the iv ready
and an infusion rather than a bolus injection.

And achieve a steady state,
then increase your mechanical index,
which basically breaks all the bubbles.

And then you watch the reperfusion,
and you can calculate the beta from the slope of this line,
and the alpha from the slope of the line
and the beta from its height.

And you can come up with a number
that roughly quantitate perfusion.

Tumor Response Applications

So let's look at the first new application
that is tumor response.

There's a group of physicians in
France at their cancer hospitals led by Dr.
Nancy LaSalle.

This was first very nicely
detailed in an article in radiology in 2011 where
they studied patients with hepatocellular carcinoma
and their response to anti-angiogenic treatment.

And she found that the waveform
and analysis that I went over were quite predictive
of tumor response.

And in cancer, what's called the progression-free interval.

And in fact, overall survival.

So the microbubble profusion assessment does correlate
to both short term and long-term tumor response.

A similar study was reported by Williams looking at
the tumor response of microbubbles, a tumor response
to an anti angiogenic agents in renal cell carcinomas.

And he found that the findings on microbubble profusion
actually predicted tumor response much earlier
than changes in tumor size, which is the resist
category used for CT assessment of tumor response.

There is other papers that have used this
and I've including them here.

There's a recent paper on perfusion changes
in cervical carcinoma with successful anti
with oncologic treatment.