- [Woman] I agree with that, I actually don't like.
- [Matthew] All right (clears throat)
can everyone hear me okay?
You don't all have to respond.
If you can't hear, you can just send a message
through the discussion or chat function of the,
of the zoom interface and I'll be able to see that
and can can answer or if you're having trouble hearing,
you can just also speak up and, and let me know.
So welcome to "Human Anatomy Through Medical Imaging"
or Rad 396 as it's numbered
in the forthcoming course catalog.
I'm Matt Geeslin.
I'm one of the radiologists here at UVM MC
and one of the co-directors of this course.
You'll hear from Dmitriy Axelrod in the second portion
of this first lecture, who is the other co-director
for this course.
And then you'll hear from a number
of other subspecialty faculties throughout the,
throughout the course as a whole covering all of anatomy.
Today's lecture, well I'll also note this,
you'll be getting communication, obviously,
through Blackboard, which if you're here,
obviously you've got it already.
And Christine Boomer and Jess Mattson Gammel
are also helping out with this course
and do basically the, all of the administrative work
that is required to make this course happen.
And we couldn't do this without them.
And so you'll, you'll also likely be hearing
from them throughout the course.
And so just to put that on your radar.
So I think Jess and Christina
are probably joining today as well.
So hello, and thank you again.
So, let's talk quick about the first lecture here.
Given that this is a course in human anatomy
that is gonna be conveyed through medical imaging and,
and in several of the, if not all of the modalities
in medical imaging, we think it's appropriate
that the first lecture be an introduction to,
to the imaging modalities that you will see
throughout the course.
This is a two-part lecture.
And the first, the first part,
which I will give I'll cover radiography, fluoroscopy,
computer tomography, or CT scans and nuclear imaging.
And this will be very macroscopic
and so there won't be a great deal of detail covered here.
What you will find throughout the,
the lecture is, or are, slides that,
that are marked with some kind of icon.
And those are, can be noted
or remembered as slides that are,
are viewed as particularly important for,
for learning by the lecturer.
You'll also find that it is mentioned
in the syllabus that if it's not in the lecture,
despite the fact that we have textbooks for the course,
which we certainly refer you to for,
for a more detailed description,
what you're responsible for
on the exams is what's, what's covered in the lectures and,
and not beyond that.
But reviewing the text is also helpful.
It puts things in context for,
for the anatomic concepts that we, that we covered here.
So the goal of this first lecture
with imaging modalities is to introduce the modalities
as a whole and, and these modalities that we use
to convey the anatomic structures
and the relationships between those structures
throughout the course,
and then do just sort of a qualitative survey
of the physics underlying each modality.
They're not gonna be any equations or anything like that.
It's just to give you an appreciation of the physics
that have to be attended to when you,
when you think about image modality development and,
and utilization thereafter.
But before we go into that we'll,
I'll introduce a slide here that will be relevant
throughout the course and that is the anatomic planes.
This slide is taken from Moore and Dalley,
one of the texts for the course.
Here you can see "Clinically Orientated Anatomy."
(clears throat) Which is available
through Dana Medical Library.
And here the planes, as we term them medically,
are the sagittal plane here on the left,
the frontal or coronal plane,
we use the term coronal here. in the middle.
And then the axial plane here on the right.
And we'll recur to that,
that becomes particularly relevant
with three dimensional reconstructions
or multiplane reconstructions, which are used in CT and MRI.
So to, to some degree of the physics.
When we think about particular the modalities
that we'll be discussing today, radiography,
fluoroscopy, CT, and nuclear medicine,
we have to think about them in the context
of the electromagnetic spectrum.
So here probably a familiar figure to,
to many, if not all of you,
we have the electromagnetic spectrum.
In the middle here, visible light.
Just to the left of visible light ultraviolet light.
And, and just to the left of visible light
is when things start to become worrisome
for damage to the human.
And, and so the first several modalities we,
we will review are, use x-rays as sort
of the workhorse for image generation
and the last one, nuclear imaging, uses gamma rays,
as well as alpha and beta rays.
One thing to note with regard
to the electromagnetic spectrum,
and I have some equations listed down here.
It's not because it's, you know,
required for memory or, or deployment.
It's just to give you a sense of the relationships
between the variables.
So on the left side of the electromagnetic spectrum,
you'll note that the wavelength is quite short,
the frequency is high.
So if you look at the energy here related to frequency,
you'll note that they are directly proportional,
and you also can tell, oops, going back,
from the electromagnetic spectrum,
shorter wave length has higher frequency, higher energy.
As we to go to the right side of the spectrum,
we have a longer way of length here
resultant to lower frequency and a resultant lower energy.
So let's begin with radiography.
We'll go through the radiation used in these modalities.
So radiography being the modality.
Then we'll go over the generation of,
of the radiation used, how we detect that radiation,
and display it to form an image,
and then some of the uses for this modality.
And if you ever see a link in the PowerPoint
or in a, a PDF of the lecture, you can,
you just copy paste that into a browser,
and it will have a relevant, a relevant video.
In this case it's one of radiography.
All right, so when we think about radiography,
let's begin with generation of x-rays.
Here to the right we have a illustration
or a cartoon of an x-ray tube.
And an x-ray tube is required for the generation of x-rays.
In this process of x-ray generation from an x-ray tube,
electrons are quote unquote,
"boiled off" what is called a filament.
And the filament here is this green wire
within the cathode component of an x-ray tube.
And when these electrons are boiled off,
that is called thermionic emission of electrons.
Once the electrons are off the filament here,
they travel, or they exist in the space
between the cathode and the anode.
And a high voltage is applied between the cathode
and the anode in order to attract
and accelerate the electrons across the space,
and to collide them with the anode here.
This entire structure here is called the anode.
Upon striking the anode,
the electron, the electrons upon striking the anode,
a variety of events that occur,
including the one we're interested in
which is x-ray radiation.
We also produce things that,
that are not useful for image generation,
including photo electrons, auger electrons,
and of the least use but of some
of the most significant design aspect of an x-ray tube
is the large amount of heat that is generated
when these electrons are accelerated at the anode target.
And this small little red line here denotes the target.
You'll note one up here as well.
And I'll explain why you see that on the next slide.
So with respect to the heat that is generated
on the focal spot, again, red lines on this anode.
When, when the electron beam collides with,
with the anode we rotate or modern elect,
x-ray tubes, rotate the anode, denoted here by this arrow,
so that that heat is dispersed and,
and this avoids the entirety of the electrons accelerated
across that space colliding with one point on the anode.
This is important because of heat generation.
And with regard to that heats
or temperatures can reach up to 4,000
or above 4,000 degrees Fahrenheit during
what's called an exposure,
which is really just saying while the,
while the x-ray tube is on.
So as a result of that,
the anode has certain material requirements,
chief among them being
that it has a very high melting temperature.
Two metals are often used one being tungsten,
which you'll also note at least in former,
former light bulbs, the filaments is tungsten and,
and another is molybdenum.
Once the x-rays are generated, they exit inferiorly here,
the x-ray window.
So more x-rays are generated
than just exit the x-ray window,
but we are only interested in capturing those
that exit the x-ray window
because they are traveling in the correct direction
for image generation.
Everything else is absorbed by the encasement here,
usually lead, of the x-ray tube.
All right, so here I have the x-ray tube turned
on its side for illustrative purposes,
and we'll think about now detection
of our x-rays that we have generated.
So once the x-rays exit the x-ray tube,
they diverge toward the patient in straight lines.
So think of this as a point source.
Upon reaching the patient, these x-rays will interact
with various tissues in the patient labeled here.
So we have heart, we have back.
This would really be vertebral bodies.
So we have lungs, lots of air in the lungs.
And then we have some peripheral soft tissues here
denoted in gray along the outside of the patient.
X-rays are attenuated or another,
another way to think about it that is stopped
by the tissues within the patient,
as a function of the density of the tissue
with which they interact.
So if you have a high density tissue like bone,
bone is going to do a good job stopping x-rays.
So bone will attenuate an x-ray.
When you, when you stop an x-ray prior
to it getting to the detector,
that information or lack of information is used
in image display.
So thinking about image display,
here we have our x-ray tube, which is our source.
Our x-ray divergence toward the patient.
A very simple detector drawing here behind the patient,
where the x-rays are detected,
and then the ultimate display.
So once an x-ray interacts with the detector, right?
That, that means that it got through the patient.
In so doing that x-ray will interact with a detector
and an, and an energy conversion takes place.
So the, the incident x-ray and photon
will be converted to, to electrical energy.
So we're going from electromagnetic energy
to electrical energy and,
and we're using that electrical energy
to create a signal that is then used for image display.
And this image display, it produces a map
in the case of radiography and,
and computer tomography, and fluoroscopy
of the relative density or,
or attenuation of patient tissues
through which the x-rays have passed.
So the spectrum of x-ray attenuation ranges from,
of course, entirely, which can be the case in bone
or partially, which you might see in soft tissue
or not at all, if it just goes through air,
such as certain, certain areas of the lung.
So here we have it, the relative densities.
White on an x-ray, for example,
corresponds to significant attenuation
for a conventional radiography.
So here we see white corresponding to the bones,
bones we know are dense relative to soft tissue
and certainly to air, and so that attenuates
or stops the x-ray before it gets to the detector.
And the detector can assign, produces,
is able to, is able to display that
in comparison to the other relative densities
through which the x-rays pass.
Same example, black corresponds to little or no attenuation,
i.e. a large number of x-rays made it
through this part of the patient in this case the lung,
and then interacted with the detector.
(clears throat) All right, this is a great segue for the,
the classically described radiographic densities.
So here we have them numbered one, two, three,
three again, four, and five.
So number one air, or lung, air being in lung,
is the lowest of the radiographic densities.
So it's very lucent.
Number two, here this one is a little bit tricky
to perceive because there's, it's kind of hard
to find fat on an, on an x-ray.
Much easier to find it on CT.
But here we have what is a fat plane
between two muscles like the,
the latissimus dorsi peripherally here,
and the serratus anterior.
Three, we have soft tissue shown here,
three and three and shown up here as well.
And in this case, that would be muscle
and overlying skin.
Four, we have bone, so we have four here
on the lateral clavicle throughout.
We have all of the ribs, the scapula,
we also have a four on the finger, bone on the finger.
And then the fifth is metal and here we have a foreign body
in the patient's finger staple.
All right, so some examples and uses
of radiography here shown we use radiography
for quick scanning for pathologic processes.
So radiography is great for detecting fractures,
great for detecting foreign bodies,
usually pretty good
at detecting cardiopulmonary emergencies,
such as a pneumothorax, which we have an example of here.
This, this lung is too black compared
to the contralateral left side of the lung,
which is hyper dense or of increased density.
And that's because there's too much air here.
And that's because there's air
between the chest wall and the lung.
So it's in the pleural space
and that is termed a pneumothorax.
All right.
Brief examples of radiography.
Fluoroscopy, again, we'll go through this
in the same format.
The radiation used, how we make it,
how we detect it and how we use it to display an image,
and then finally some uses.
So fluoroscopy suite, here we have two examples.
On the left, we have what's called
a biplanar fluoroscopy suite.
This is typically used in more complex image interventions,
such as neurointerventional, radiology,
or innervate body interventional radiology.
Here on the right, we have a gastro GI fluoroscopy suite,
which is optimized for doing procedures,
such as barium or Omnipaque swallows, contrast swallows,
swallow studies, so we're looking at the esophagus,
the stomach and, and the small bowel
and large bowel as it goes through the body.
Image generation, when we think about fluoroscopy.
So again, fluoroscopy uses x-rays just like radiography.
And so we need an x-ray tube, we need a detector,
and we need a mechanism for displaying the image.
A big advantage of fluoroscopy is in
that it can be done in real time.
And that's why it is used for image guided interventions.
It's particularly useful for image guided interventions.
Additional areas where you'll see fluoroscopy,
which we described previously is the barium swallow,
so you're swallowing a radiopaque agent such as barium,
and you're watching that agent travel through the,
the esophagus, stomach, and more distal to that,
as it goes through the body.
An additional one, coronary angiography,
both YouTube videos are provided here.
Other, other uses included,
include image guided interventions,
which I touched on briefly, including neurovascular,
cardiovascular, peripheral vascular, and joint injection,
as well as gastrointestinal diagnosis and,
and rarely intervention.
Computed tomography, same pattern.
What's our radiation.
How do we make it?
How do we detect it?
How do we display it?
And what do we use this modality for?
All right, so here we have, just checking the time.
Here we have two images of a CT scan
or the one on the left with the scanner cover removed.
So here we can see the row of detectors.
We talked a little bit about detectors in,
in the previous modalities, in particular radiography.
So that is, that is the mechanism.
That is the part of this machine,
which allows us to convert our electromagnetic energy,
our x-rays into electrical energy
so we can get an electrical signal and make an image.
Up here, directly across would be the x-ray tube
or the source.
In here, image on the right.
We have just a CT scanner with (clears throat)
Excuse me, with the cover on.
So this is what it looks like.
So the components going a little more detailed
include a power source, of course,
the x-ray tube or tubes,
many CT scanners actually have two,
two x-ray tubes in them, which allows more,
more clever and sophisticated image reconstruction
as well as diagnosis based on each,
each x-ray emitter or each x-ray tube
putting out x-rays of a different energy.
And if you print out x-rays of a different energy,
you can, you can do work with those different energies
for image reconstruction and, and diagnosis.
We have a table mechanism for positioning the patient
and moving them through the scanner.
We have the scanner console here,
including the computer room,
where also the image reconstruction software is deployed.
So the process of obtaining a tomographic image
or a CT image is, is not,
it's very similar to, it's not dissimilar,
it's very similar to obtaining a radiographic image.
We have an x-ray tube here, focal spot shown.
We have the rays, x-rays, divergent from that tube
traveling toward the patient.
And then we, the patient here is the purple and the yellow.
And then we have a row of detectors to detect the,
the x-rays that are incident upon,
upon that row of detectors here again.
Detectors, x-ray tube or the x-ray source.
And so we'll note here the word profile and,
and sort of a graph that is displayed
along the course of the row of the detectors.
Pay attention here to, to these individual x-rays
as they travel toward the row of detectors and,
and think about whether they are passing
through the patient, not through the patient,
through the peripheral, or are they outside of the patient
or through the middle of the patient.
So you can see this one here passes entirely
through the air.
So it goes, it goes past the patient
without passing through it.
You'll see this profile here is a graph
of the intensity of the x-ray on the,
or the summative x-rays on the, on the detector.
So when an x-ray is not stopped
before it gets to the patient,
or x-rays are not stopped before they get
to the detector, I'm sorry.
You have a higher intensity of x-rays on the detector.
And that's what this profile is, is represented.
And this profile is used mathematically
to ultimately create the image that is displayed for,
for CT scans.
So relative to the outside or beyond the patient,
look right through the middle of the patient
and you'll know it's the lowest profile
or the lowest intensity of incident X-rays.
This next series of figures shows basically the same thing.
To the left here pretend this, this ribbon arrow,
if you will, is the row of detectors
as it goes around the patient
so that the detector spins around the patient
as the patient is moved on the table through the machine.
And as a result of moving the patient while you spin the,
the source and the detector,
you image the entirety of the area
of the patient that you wanna image.
So in this case, it looks like they're trying
to image the patient's chest.
I can see the arms here, see the patient's chest here.
The cartoon or the illustration to the right here
shows how the x-ray intensity or the profile changes
with different projections or different angles
of the focal spot relative to the patient.
So here we have it directly above the patient passing
from front to back, going through the lung,
the heart, the peripheral soft tissues.
And we can see the varying intensity
of the x-rays that are incident on the detector,
based on the tissues through which they pass
on their way to the detector.
Here taken from another point.
Remember this is that, that scanner gantry
that's twisting around the patient.
So it's moved to the left a little bit,
and now it's shooting x-rays through the patient
from a different angle.
And as a result, it produces a different,
an x-ray intensity profile.
And all of this is taken together
and math done based on it
to produce the reconstructed image.
So we have x-rays go through the patient,
hit the detector, produces the profile.
That profile is converted from electro magnetic
to electrical energy that produces an electrical signal.
That signal is used in the computer,
received by the computer, used by the computer
with complex mathematics to ultimately create
an image display, which we have here on the far right,
which is a coronal chest CT.
And I have here denoted lung windows.
You won't be responsible for windows.
It's just to, to illustrate
that you can window CT images differently
to highlight certain features of,
of the anatomy which you are imaging.
So back to anatomic planes,
which I said is gonna be particularly useful
when you think of cross-sectional imaging like CT and MRI.
We have here the sagittal plane,
so we can see the spine nicely profiled.
We have the coronal plane,
we can see the liver and the kidneys
and the spleen nicely profiled and the bones of the pelvis.
And then we have the axial plane,
which I'll note, I don't have it labeled here,
but it is actually the left of the image,
which is the right of the patient.
And sometimes, sometimes if you forget that and it's,
if it's relevant based on the image you're considering
you can, you can use a little cheat
to figure out right and left by knowing the side
of the organ that you're looking at.
So in this case, we have a liver which, which you know,
or will learn as on the right of the upper abdomen.
So this one we know.
Barring any anatomic abnormality, of course,
we know that we're on the right side of the patient here.
(sighs) All right, some quick uses of CT scan.
CT is used a great deal in, in medical imaging
and as you can see here, there are several uses.
So we have a head CT scan.
We have an axial chest CT in the axial plane
of a chest CT scan, which you've seen already.
We have a coronal CT scan of the abdomen,
showing the abdominal organs here, liver, small bowel,
large bowel, spleen, stomach to name a few,
you'll go into more detail with that as you get
to the chest abdomen section of this course.
And then reconstructed cardiac CT showing
what is likely the left anterior descending artery here
displayed showing coronary plaques.
I'm sorry, left coronary artery here showing plaques,
areas of stenosis, and this reconstructed
to show the sagittal projection of the heart
in this case, the left ventricle,
as well as the axial projection of the heart
in this case here left ventricle.
And finally a 3D reconstruction also obtained with CT.
Quick comment on contrast administration.
So CT, one of the additional uses of,
or pieces of CT that make it quite useful is that you can,
you can add contrast agent,
which is something that attenuates x-rays,
and you can add that by adjusting it
so it goes through your gastrointestinal system
from esophagus to stomach, to small and large bowel.
You can also give contrast or administer contrast
through the, through a peripheral vein,
in which case you will be opacifying the vasculature.
And you can, you can image at different times relative
to the time point at which you injected
to produce different a enhancement pattern for your image.
So we have that shown here.
We have an unenhanced CT scan.
So in this image or two images on the top left,
no contrast was administered either ingested
or intravascular.
The image on the top right,
we have two contrast agents on board.
We have an intravenous contrast agent,
which can be inferred by opacification of the portal
and hepatic veins within the liver.
We also have an, an oral contrast agent
that has been administered and that is,
can be, can be inferred by the relative opacification
of the small bowel here, left hemiabdomen,
and the large ball here, right hemiabdomen.
And then lastly, here we have a different phase
of intravascular contrast administration,
the arterial phase.
So here we can see the aorta shown here in,
in cross section or in the axial section
and as well the aorta and portions
of the heart shown coronally.
And just drawing your attention here.
So we have an axial image, right?
Portal venous phase axial image, arterial phase.
Note the difference in the appearance of the kidney,
there's the kidney, portal venous phase
and the kidney on the arterial phase,
the enhancement pattern varies.
And that's illustrated here best probably with the kidney.
All right, on to nuclear medicine.
So same, same pattern, right?
Radiation first.
How do we get it?
How do we detect it and how do we display it?
And then what do we use this modality
or these modalities for clinically?
To the right here which, which is shown
and can be seen by clicking the link
to the website is a cardiac nuclear medicine test
looking for cardiac viability.
So they're looking there, looking for areas
of decreased blood flow or perfusion is the,
is the word used in, in the heart.
And you can see it shown here
in multiple different projections.
So an axial, sagittal and, and coronal.
Okay, so nuclear medicine, some basics here.
The radiopharmaceutical is a term
you'll become familiar with
and radiopharmaceuticals are compounds
that contain small amounts of radio isotopes.
Radio isotopes themselves are produced (clears throat)
Excuse me, in nuclear reactors or particle accelerators.
Radio isotopes upon being produced are then tagged
onto certain molecules based
on their biologic characteristics.
Once a radio isotope or biological molecule are joined,
a radiopharmaceutical is born.
Upon administration of the radiopharmaceutical the,
the drug migrates to the region of the body where,
where the specific molecule is biochemically processed.
And that underlies the whole point of a radiopharmaceutical.
We want these agents to be taken up
in particular areas of the body
to emit radiation from there
and then we detect that radiation.
We infer based on their concentration in certain areas,
the presence of the body, the presence,
or absence of the pathologic process.
All right.
So, couple more basics on, and distinctions in particular,
with nuclear medicine compared to other,
other modalities that we reviewed today.
So nuclear medicine involves the detection
of radiation that has been administered
from within the body.
So the radiation is inside the body
and it's being emitted from within the body.
And we are detecting it as it, as it (stammers)
exits the body, if you will, using our image detectors and,
and the radiation again is gamma, beta, and alpha rays.
CT, the other modalities that we reviewed,
CT, radiography, and fluoroscopy involve the administration
of radiation from outside the body,
passage of that radiation through the body,
and detection of that radiation
on the other side of the body.
Another point about nuclear medicine is
that it can be used for both diagnostic purposes,
as well as therapeutic purposes.
So because these, these agents, or the radiopharmaceuticals,
emit radiation, they can not only be detected,
but as you probably know, radiation can be used
to destroy unwanted tissues such as malignancies or cancers.
And so you'll, you may find as the course progresses,
that certain, certain uses of therapeutic radiation
are reviewed for, for the purpose of,
of reviewing certain anatomic concepts.
All right, so nuclear medicine process.
Cyclotron on the left, that's used
to produce the radiopharmaceutical.
The radiopharmaceutical is administered into the patient.
The patient is scanned on, on the machine,
in this case a PET CT scanner and,
and the radiation emitted is detected by the machine.
So in this case, we have a PET CT scan,
which produces three separate,
three separate sets of images, a CT scan, a PET scan,
and then a combined CT PET scan.
So these are the most useful of, of these two,
this set of three images.
And here you can see areas of increased metabolic activity.
So in this case, we have a mass in the right hilar,
you know, the right hilar region,
which is likely why the patient
was being imaged in this case.
Additional uses, so here's an example of a bone scan.
Again the, the agent used for bone scan,
which I review here, it's called Technetium 99.
You don't have to know that aspect
but it travels to sites of increased bone turnover.
And as a result, this agent has avidity
for skeletal metastases.
And so here we have an example of a bone scan
with multiple skeletal metastases.
And then another, another and probably the most
widely known use in nuclear medicine
is the PET CT scan, which was,
was what we looked at on the first image.
So here we have a PET CT scan, a fused image
in the coronal plane.
And we have an area of increased metabolic activity.
It's a mass in the left upper lung.
And we know based on the increased metabolism,
or we infer, that it is likely a malignancy.
Malignancies having relative increased metabolism.
But not all areas on PET CT are areas of,
of abnormal increased metabolism.
Here we have that shown on this axial plane
showing the outline of the left ventricle,
which is also understandably hypermetabolic.
And then the last point about PET CT scan,
which is similar to what we noted in bone scan
is that nuclear medicine takes advantage
of biochemical processes.
In the case of PET CT scan,
the radiopharmaceutical is injected and,
and taken up by, by the cells of interest
in which it is further broken down.
Tumor cells, as we talked about previously
have have a higher metabolic rate compared
to normal cells in most cases.
And, and thus this compound is metabolized
relatively increased by by tumor cells.
And so we'll see a higher concentration
of our radiopharmaceutical
and thereby the radiation emitted in, in abnormal cells.
And so if we have that perfectly demonstrated here
with this increased, area of increased metabolism
in a mass where it doesn't belong in the leftover lung.
So thank you, questions, if you have any,
you can also send Dmitriy or myself an email
Dmitriy is gonna start right now.
And again, thank you for being here.
We look forward to having you in the course.
Dmitriy is getting set up here.
Do you guys have any questions in the meantime?
- [Woman] I think someone posted a hypothetical question
about x-rays in the chat.
That seemed kind of interesting.
- [Matthew] Okay, let's see here.
Oh, chat, yep, sorry.
I said I was gonna look at these
and then got carried away.
So we can hear you.
Know anatomic locations that you described, no.
Are you supposed to know the anatomic locations?
No, certainly not yet.
I guess that's, that's the short answer there.
No, don't worry about that yet.
It's, it's merely to, to illustrate whatever point
I was trying to make, trying to make about the,
the image modality that, that I was describing.
Would angiography be performed in the biplanar suite?
Yep, that's it would.
So in particular cerebral angiography.
And the reason for that is because localize
in the vessel that you are trying to opacify
or evaluate, hopefully it's opacified,
although it may not be and that's why you're
in the cerebral, why one would be
in the cerebral angiography suite.
So, so yes, let's see.
Weird theoretic.
So question, it's not a weird question, so don't worry.
Is the layout of the CT scanner source
and detector similar enough to standard 2D x-ray
that one would be able to simulate a 2D x-ray
from a stationary CT scanner?
Let's, let's come, I'll remember that.
I'll take that question down
and I'll answer it in the next lectures.
'Cause Dmitriy is ready to get started.
So I'm, I'm going to, and there are two more here,
so I will write those down and I'll answer them
in the next lecture, if that's okay,
which will be Wednesday and I'll sign off here
and let Dmitriy get started.
- [Dmitriy] Everybody this is Dmitriy.
Can you guys hear me?
- [Student] Yeah, we can hear you.
- [Dmitriy] Okay, great, thank you.
Sorry, I got held up by some clinical patient care issues.
I'm gonna start up my PowerPoint here.
I was hoping to get an ultrasound machine in here
to show you guys how it works,
but I'm not sure that's gonna be.
Well, I couldn't get it (laughs)
I just got held up.
So here's my screen.
Let's see.
Okay, do you guys see my PowerPoint here?
Just to make sure.
- [Student] Yeah, we can see it.
- [Dmitriy] Okay, great, thank you.
Okay so (clears throat)
Welcome everybody, I'm Dmitriy Axelrod.
I'm the co-director of this course.
Hopefully you had a great time with Dr. Geeslin
and that he's shown you how you can make some mutations
with our radiation and such.
This will be something completely different.
We will look at some non-radiation,
non-ionizing radiation based imaging techniques.
So we'll start with ultrasound.
So the way that ultrasound works is different
from the x-rays that you were talking about earlier
and nuclear medicine,
which is on the electromagnetic spectrum.
We work in the ultrasound or the sound spectrum,
and the sound spectrum here is described,
infrasound, acoustic sound, which is the sound
that we can actually hear, ultrasound,
which is sound above what we can hear.
It goes anything above 20 Hertz.
So for humans, anything between 20 Hertz
and 20 kilohertz is a acoustic sound.
And so while the electromagnetic spectrum is,
describes the moving, movement of charge particles,
sound as a mechanical energy disturbance of,
of a medium, and in the case of audible sound,
the medium is air.
So it's mechanical disturbance of air that we are,
our eardrums, are able to hear as sound.
So again, ultrasound is anything that's above audible
or above 20 kilhertz here.
So why is ultrasound important?
Why is it so, so amazing?
And it's certainly come, come a long way,
but the important thing about ultrasound is that it's,
no ionizing radiation is used
and in the diagnostic range of frequencies of ultrasound,
there is no soft tissue damage at all.
And we'll talk about safety a little bit later.
The other thing about ultrasound is that it's real timing
that as we're scanning, we're seeing what,
what is happening in the patient,
and we can adjust our scanning parameters
or adjust where we're scanning based
on what we're seeing right away,
instead of a, more of a shotgun approach
with something like CT or, or x-ray
where we're just imaging an entire area
and trying to figure out what we, what we see.
Here in ultrasound, we pick what we wanna see
and we try to see the best we can in real time.
And over the last many years,
it has become much more portable.
As you can see here, there are handheld wifi probes
that you can take anywhere, anywhere you want
as long as you have a cell phone.
And so it has made ultrasound very accessible,
relatively inexpensive, and really ubiquitous,
including something called point of care ultrasound,
which is where a non radiologists are able to use ultrasound
in their clinics or in the ER, to make diagnoses,
without having to involve the Department of Radiology,
which in some cases is, is good
and in some cases is questionable.
But a very important diagnostic tool, nevertheless,
with appropriate training.
So this is kind of one of the images
of early ultrasound equipment, as you can see.
Not terribly portable, and this was done as an experiment
in a, in a water bath.
And the reason there's a water bath is
because you need to have a medium
for the mechanical, you know,
energy disturbance to happen in.
And we'll kinda get into that in just a second
about why you need to have some kind of a medium.
So what are some physical concepts in ultrasound?
Sound can't exist without a medium,
and that's why in a vacuum, you can not,
there is no audible sound.
And so it's produced again by mechanical disturbance
of the particles in that medium.
And it's, you know, it's a transfer
of kinetic energy when that disturbance occurs.
So this transfer of energy results
in alternating compression and refraction
of the particles in that medium
as the sound wave propagates within the medium
and diagnostic ultrasound operates at anywhere
between one and 20 megahertz.
And you remember anything above 20 kiloshertz
is above audible sound so ultrasound.
This graphic doesn't seem working
but a transverse wave is one that goes like this,
which is what this is.
And longitudinal wave is basically a compression of the,
of this spring, ya know, closer together and further apart.
And so this graphic here shows that in here there's a,
there's a progression or sorry, compression,
and here there's, there's rare fraction.
So here you can see the particles are coming closer together
and they're coming further apart here.
And so as the sound propagates,
it keeps causing this compression in rare fraction.
So how do we generate an ultrasound image?
So the transducer that we use transmits sound waves
into the body and the sound waves are reflected off
of the different interfaces inside,
that it meets inside the body.
And then when it meets these interfaces,
the sound bounces off and comes back
and returns to the transducer.
And that's how we see what's happening inside.
And then an image uses, the information is then used,
to create an image based on what sound waves come back
to the transducer.
So the first part where the transducer transmits sound
or pressure waves into the body.
And so the way that works inside the probe
is that the electricity is applied
to something called a piezoelectric crystal
and piezo means in Greek pressure,
electric from the word electrum or amber,
because when you, if you were, apparently if you rub amber,
it causes an electrostatic phenomenon
so that's where the word electric came from.
And then most natural crystal,
and that's what was used originally
in ultrasound probes is quartz, but it's,
it's very difficult to use because you have
to shape it appropriately.
And so now ultrasound probes use man-made materials
to improve the performance of the crystal.
And that's why the ultrasound probes that we,
that come along with the machine are very, very expensive.
Some of the probes are up to, you know, 15,
$20,000 just for the probe.
That's not even including the machine itself.
So those, those crystals are very expensive.
So what happens is the alternate current,
alternating current is applied to the crystals,
which results in vibration of those crystals
and the vibration applies mechanical,
results in the mechanical pressure
or a pressure wave that is exerted
onto the adjacent body part.
So the, the wave is produced by vibration
of those crystals on the skin.
And so then the sound waves are reflected off
of the interfaces and then when they,
when they reach, ya know, various organs inside the body
and then the sound waves return to the transducer
and then the, this piezoelectric crystal works
in the opposite way and converts the,
the pressure energy or the mechanical electric
that comes back from the body to the transducer,
converts it to electrical AC current.
And then the AC current is what goes back to the machine
and tells the machine what the probe is, quote unquote,
"seeing" inside the body.
So these crystals work in both ways, forward and backwards.
So the image is generated based
on when the returning waves are received
or heard by the transducer.
So the structures are displaced closer to the probe.
So here is what we call the footprint of the probe.
This is a curved probe here.
And if a object is really close to the probe,
the sound wave being reflected off
of that object will return sooner.
And so this scalp of this little baby,
the sound off the scalp, reflecting off the scalp,
return to transducer first.
And that's why the scalp is first
in the image closest to the transducer.
And the further away we go, when we get to the ventricles
of this head, you know, the further out we go,
the longer any of these echoes took to get back
through the transducer after being admitted.
And so, again, the structures are displayed closer
to the probe were the first waves
to return back to the probe
and the structures are displayed farther,
farthest on the image from the probe,
were the last waves to return back to the probe.
And you can see, you know, sort of the fidelity
of the closer structures is much better than fidelity
of the farther structures,
because many more sound waves get bounced off here,
than the ones that get bounced off back here,
because there weren't as many left anymore to bounce back.
So, so what's the importance of the ultrasound gel?
And if any of you have had an ultrasound,
you know, you get covered in this goopy stuff,
and what it does is it prevents any air gaps
between the probe and the, the body,
because when, when the sound beam
or the sound pulse, encounters an interface
of two materials which have a large difference
in their propagation velocity,
most or all of the beam ends up being reflected.
So between the probe and the air,
there's a very large difference in propagation velocity
and so most the sound beam will get reflected
right back to the probe so you get no information.
So if you don't put gel between the probe and the skin,
all the air that gets trapped between the probe
and the skin will reflect a lot of the sound beam
and so you have very poor image.
The gel kind of matches the difference
between the propagation velocity of the,
of the probe and the propagation velocity of the body.
And so all the sound beam,
or as much of the som beam as possible,
gets from the probe into the, into the body.
And so, and this is because of acoustic impedance,
which is, which is dependent on this propagation velocity.
And we're not gonna really discuss acoustic impedance here.
It's, it's too in depth.
So the gel, again, it eliminates that large velocity change
caused by air between probe and skin.
So you can see the propagation velocity of air is 330
whereas most of our sort of soft tissues
are in the 1500 range.
So that's too much of a difference
and so most of the sound wave would be reflected.
All right, so this is hopefully gonna work
and will allow us, or allow me, to use Dr. YouTube
to show you guys the concepts we just discussed graphically.
Let's see if this works.
(faint music)
Let me see if I can fast forward here.
(faint music)
- [Narrator] The heart of most ultrasound systems
is a device called a transducer,
which uses an array of piezoelectric crystals.
- [Dmitriy] So here's one wave of crystals.
- [Narrator] Vibrates when an electric signal is applied,
producing high frequency sound pressure waves,
which we call ultrasound.
- [Dmitriy] Before I go on,
can you guys hear the captioning or no?
- [Student] Yeah, we can.
- [Dmitriy] Okay, good I was.
Otherwise I could do it.
Okay, here we go.
- [Narrator] More importantly, this type of crystal
can also work in reverse.
It can produce electrical signals
when it detects high-frequency sound pressure waves.
When a transducer directs ultrasound waves into the body,
they pass right through the skin
and into the internal anatomy.
As the waves encounter tissues
with different characteristics and densities,
they produce echoes that reflect back
to the piezoelectric crystal.
This happens more than a thousand times a second.
Return echoes are converted to electric signals,
which a computer converts into points of brightness
on the image corresponding to the anatomic position
and the strength of the reflective echoes.
A medical transducer contains a larger way of crystals,
which allow it to make a series of image lines
that together form a complete image frame called a sonogram.
In addition, all the crystals are repeatedly activated
many times in such a way that a complete image frame
is formed around 20 times per second.
- [Dmitriy] All right so get, that gives the idea
of basically what I talked about 15 years,
15 minutes in less than a minute, which begs the question,
why don't you just watch YouTube videos to learn anatomy?
And I don't have a good answer to that question.
But let's move on, so probe selection.
So again, these are the probes I was discussing.
There are different types, some are external probes.
So this is the curvilinear probe, I mentioned.
This is a linear probe.
This is what we call a hockey stick probe.
And I think it's called a hockey stick all over the world,
not just in Vermont, because of our hockey history,
but this one here is called an intracavitary probe.
So this is an endovaginal probe.
So this allows us to see things like uterus
and ovaries much better by doing transvaginal ultrasound.
And depending on which probe you use,
the profile of the sound beam is gonna be different.
So for example, here in a lineary probe, you know,
the sounds comes out just straight out,
whereas in a curvilinear probe, it comes out at an angle
and so you see a lot more of the body than you would
with a linear probe.
Whereas with a phased-array probe,
you have one focal point of,
of where the crystal emanates its beam
and it gets fanned out and then comes back
in the same fanned out way to the probe.
And so you're able to get, for example,
between the ribs with this phased-array probe,
but you won't have as much resolution as you would
with a curvilinear probe or a linear probe.
So you're gonna have a harder time seeing.
Okay, this is a different type of a probe.
This is from endoscopists.
So a gastroenterologist can go in and do,
you know, do endoscopy, take a look at the stomach,
take a look at the duodenum
and then they can use an ultrasound
through the same endoscope here to look
at the pancreas because you can't see the pancreas
from the lumen of the stomach,
but they can look at the pancreas through the wall
of the stomach and if they need to,
they can biopsy a pancreatic cancer
or any kind of pancreatic mass with this needle here
that is guided by the ultrasound machine.
So this is what the gastroenterologists can do
in their endoscopy suite.
This is a transrectal probe
and urologists use transrectal probes
to guide their biopsies of the prostate gland.
And so this is another utility,
and unfortunately there are a lot of prostate biopsies,
which are very uncomfortable,
but are needed to look for prostate cancer.
So you can see, this is a needle here that goes
into the prostate gland here
and the ultrasound machine here,
the probe is right up against the rectum,
imaging the prostate, and guiding this needle
into where you want to biopsy the prostate gland.
So when you select the probe,
you look at the profile of the probe,
but you also look at the frequency of the probe.
And so the lower the probe frequency,
the deeper the penetration of the sound beam
into the soft tissues,
but you get lower resolution.
If you remember, I showed you in that,
in that little baby head, the farther that things were
the more, the less clear they became.
And so if you think about it,
well, so then the high frequency probe
won't penetrate as deeply,
but you will have much better resolution
of all those things that are just under the probe.
So you'll see things much better that are nearby.
And if you think about it, let's say you lived in a,
you know, in a house or an apartment building,
and you had a neighbor who was playing
some really loud music,
for the most part what you will hear is that,
is the deep bass, sort of the, if you think of what,
you know, I don't know dubstep or something,
and, and you hear the bass,
but you won't really hear the treble
because that's the high-frequency portion of the music.
So the low frequency, those bass sounds,
will penetrate deeper and will penetrate
through the walls and into your own apartment.
Okay, so here are some images generated by various probes.
So here are two linear probes here.
This is the linear probe I was telling you about
that had the flat face, like this,
and shot the beam straight out.
You can also do some fancy electrical work
and activate these little crystals in a,
at a different time point and that helps you steer the beam.
So even though it's a linear probe,
based on how the sound beams are interacting
with each other, it steers the beam to one side or another.
Here's another probe that's also linear,
but it has a profile like the curvilinear probe.
And again, that's based on how,
the way that these crystals get activated.
And that's, you know, this is not important for this class,
but just more point of interest that you can do
fancy things with, with what you have at baseline.
And here's a curvilinear probe,
and you can see that the kind of the resolution here
in the linear probe is trying to do fancy things
to imitate a curvilinear probe.
The resolution here is not as good as
with the curvilinear probe here.
And also you have to look at, you know,
this is the frequency of the probe.
So this is a higher frequency probe.
So it'll have nicer images nearby.
Remember the higher, higher the frequency the,
the less deep the penetration,
but you'll have a better resolution nearby.
Whereas this probe can penetrate deeper
and you can see deeper structures much better.
You can see this aorta here,
much better than the aorta here.
This is the same patient.
And this is a sector probe and the sector probe
remember I said it's, it's got a small footprint.
It's a, it's a really small probe.
You can get into tight spaces with it,
but the resolution isn't gonna be as good,
because it's trying to do a lot of things
with a very small footprint.
All right, so let's move on to safety of ultrasound.
And I'm gonna try to go a little bit faster here,
because this is all very interesting,
but we have to talk about MRI still.
So again, no ionizing radiation.
So there is no cell or gene disruption
with ultrasound, thankfully,
in the, in the diagnostic range,
but it is still mechanical energy transmitted
into the soft tissue so we are still governed
by the ALARA principle, which is the principle
that we have to use as, which is the,
As Low As Reasonably Achievable principle,
which means that we should use as little invasiveness
into our patients as possible.
And so the energy that's emitted
by the probe can also be focused.
And in that case, just like in a magnifying glass.
And so in that case, it could cause damage
and harm because you were focusing mechanical energy
and it could cause cell disruption.
So it's very important to remember that it's,
it's very safe, but in the diagnostic range.
And so, and the biggest source of harm
in ultrasound is untrained users.
And so they, they can either hurt patients
by putting too much energy into their bodies.
They can also misdiagnoses and say that nothing's wrong
when in fact there's something is wrong
and they can also make the wrong diagnosis
saying something is wrong but it's not the thing
that they said is wrong.
And so it's not just the, the physical harm of ultrasound.
It's also the diagnostic harm.
So the, you know, the energy that the ultrasonic imparts
onto patients soft tissues is measured
in the thermal index and mechanical the index.
And these are, these are terms
that you don't have to remember just important
to sort of discuss since we're talking about it.
And the thermal index is basically the absorption
of that mechanical energy by the tissue converted into heat.
Whereas the mechanical energy is that when,
when the sound beam causes refraction
or the pulling apart of particles, it can do that in a,
in a way that can cause gas bubbles within our bodies.
And so it can cause cavitation or make holes inside organs
if the, if the sound beam is high energy enough.
And so in the diagnostic range, which is set by the FDA,
ultrasound is safe when used
by properly trained individuals.
And so the thermal index and the mechanical index are,
are limited by the ultrasound machine itself.
You have to remember though in,
in babies who smaller than adults, or fetuses,
they're more sensitive to, to heat.
And so you don't wanna, in first trimester,
overheat a fetus because you could cause defects
in forming normal organs.
And so you have to be careful.
And so when we do imaging of the fetus,
we have to limit how much Doppler
and color ultrasound we are doing, because these two things,
impart the most energy in a diagnostic machine.
So we talked a little bit about,
we're gonna skip this particular video,
but we talked a little bit
about how ultrasound can cause capitation and heating.
In fact, certain machines are designed
in such a way that they, they are supposed to cause a lot
of heating and so that it can heat up to a hundred
or 600 degrees Celsius and cause coagulation.
And that can be used to focus a beam of ultrasound
and treat things like fibroids in the uterus and,
and sort of burn them without having to cut them out.
And it can also treat prostate cancer.
And you can, some people treat liver tumors
by heating them up
and basically cooking them inside the body.
And you do it in such a way that you focus the beam
that the tumor itself gets cooked,
but nothing around it is cooked and,
and no fava beans if you guys know what that means.
So, oops, and then you can do noninvasive plastic surgery,
which is basically they're heating up the collagen
that's under the skin to straighten it out as it,
as it sort of heats up, breaks up,
and as it cools off, it straightens out
and you get rid of wrinkles.
By the way I, if anybody's interested,
I do this on the side, on the weekends.
So give me a call.
No problem.
So contrast agents in ultrasound.
That's something that we talk about a lot with CT and MRI,
but you can also have it with ultrasound
and it can characterize lesions inside organs.
It can also characterize vessels
and you have the added benefit of not having nephrotoxicity
like the contrast agents used in CAT scan and MRI.
And the contrast agents are composed
of these little micro bubbles inside of sort
of fat lobules and they get injected intravenously,
they're tiny little micro bubbles
and while we're scanning a particular lesion,
let's say in the liver, we watch the,
we watch the bubbles come, come pouring into the lesion.
So here's a nice example of that.
Let's do a quick, so here's an ultrasound.
They found this mass here.
And they're gonna inject some contrast.
You're gonna watch it sort of light up.
Shortly, here we go.
So they start and inject the ultrasound contrast,
no contrast yet you start to see those gas bubbles coming in
through all the vessels.
And now the lesion is filling up with the micro bubbles.
And so, you know, this is what we call enhancement.
And we call it enhancement in CAT scan, MRI,
and this is what enhancement is on ultrasound.
Okay, so some descriptive terms that we use in ultrasound.
We use the word echogenicity
which is the amount of echos or interfaces inside something.
Something that's echogenic or hyperechoic
is brighter than adjacent tissues.
And remember everything here is relative.
Something that's isoechoic is the same
as the adjacent tissues.
Something that's hypoechoic has less echos
or is darker than adjacent tissues
and something that's anechoic at all,
or completely anechoic, has no echoes at all
and is much darker than the adjacent tissues.
So here's an example of a hyperechoic lesion.
It's brighter than the adjacent liver here.
Something that is isoechoic
and hypoechoic usually has very little sort of
useful information for, for diagnostic purposes
and then something that's oh,
so here's a mostly isoechoic lesion, here is normal liver
and this lesion is pretty similar to the liver nearby,
and it's a lot harder to see
when you don't have calipers on it.
So here is a liver lesion here.
Whereas it's very useful to have an anechoic lesion here,
which is basically a simple cyst
and it can be, in short just ignored all together.
And it's again, fluid filled structure, always benign.
Hang on a second.
I'm getting a, just wanna check the chat thing.
Oh, okay, so it's a question about what type
of gas is being used and concerns for embolism.
No, so it's not just a pure gas.
It's gas inside of micelles.
And so these, yeah, so it's,
it's these micro bubbles that are,
are inside of micelles and so they're safe.
In fact, they're used as what we call bubble studies
in cardiology to see if they cross into the,
from right side of the heart to left side of the heart
and that's expected and they don't cause embola
into the brain or anywhere else
and they just get absorbed into the tissues.
So they are, it is a safe thing to inject.
So not straight air, just to be sure.
It is a, it's a saline solution with these micelles
of gas inside of them.
The gas is protected by the, by the little lipid molecules.
So how do we use ultrasound?
The applications of ultrasound are wide here
and there's lots more.
There's, I just wanna show you real quick
about what the different types of ultrasound here.
And so, you know, so here's the 2D ultrasound.
Just, this is what we think of when we think of ultrasound.
Oop, let me go back and just.
This is what's called 3D ultrasound,
which is basically a probe gets a large, you know,
large volume of data and reconstructs it
in three dimensions.
You have to have, it's mostly done for fetal imaging
because the fetus is surrounded by fluid
so they're able to sort of do this kind of post-processing.
And then the 4D ultrasound is when you can,
can watch a baby moving around live in there in the uterus.
So that's kind of the, some of the terminology
from that perspective.
Okay, and just remember, you know,
for those of you who end up having children,
that the more scans you end up doing,
the more heat you're imparting onto your fetus.
So don't do it willy-nilly,
especially in the first trimester.
Later on when they're just about ready to come out,
you just wanna see them that's, it's okay.
There's not that much heating.
So let me just make sure I answer all the chat questions
before I go on to MRI.
Okay, good.
All right, so MRI and this,
a lot of this information was taken
from a colleague of mine,
was a physicist much smarter than I am.
So definition of nuclear magnetic resonance.
Nuclear, its property uses nucleus to give us the signal.
And so in MRI for diagnostic purposes,
that nucleus is hydrogen, which is just a single proton.
That's basically what we're imaging is the hydrogen proton
in everybody's bodies.
And so the magnetic properties of the nucleus
is what we manipulate with nuclear magnetic resonance
and MRI imaging.
And the hydrogen is one of the few nuclei
that has a magnetic moment so we're able to image it.
And thankfully, most of us are made of predominantly water.
And so lots of hydrogen molecules in us.
And then resonance is object that resinates
when they're exposed to forces at their natural frequency.
And so a example of something like that is,
is a guitar string or when the singers
are breaking wineglasses with their voice
because the match, match the resonance frequency
of the glass material.
And then same thing with the, with the bridges and the wind
is that the, the frequency of the wind gusting
matches the frequency of the bridge.
So this was a cave drawing found several thousand years ago,
predicting the MRI is going to founded in 1947
by Dr. Bloch and Purcell.
And the first clinical magnetic resonance imaging
was obtained in 1977.
So I spent some time figuring out how to squeeze all
of MRI physics into one page and this is what it is.
So you guys can, only parts of this will be tested.
Sort of the, the left mid and the left lower part
you have to memorize and the rest don't worry about.
So where does the MR image come from?
And so it's this thing, that's where it comes from,
and it comes from there and we read it and we're done
and we just move on with our day, but how does it do it?
And so, again, we're made of fluid about 70%.
And, and we, the only thing that for the most part,
the only thing that the MRI machine sees is the,
is the protons that, that's in the water.
And again, these protons have a magnetic moment
which has a vector.
And so it's, and these protons are always spinning like this
and wobbling, so it's not a straight spin.
It's always wobbling back and forth
and we call that wobble the pre-session.
Just like a spinning top here.
So again this nucleus or this proton,
it's constantly spinning and constantly wobbling.
So inside the tube, most of the protons in our body,
once we're in the tube, get aligned in the same direction
by this B0 coil.
So there's a coil that exerts a magnetic field
and that's what we talk about
when we say three Tesla magnet, or 1.5 Tesla magnet,
it's that B0 field that we're discussing.
And that's the strength of the field inside that,
inside the tube here.
And so the stronger the field,
the more molecules align along the
whatever vector you want them to align.
So that's B0 field, that's what this B0 is.
And then we use something called these gradient coils.
And what these gradient coils do is they apply
slightly different fields in different directions
inside of, of the tube, inside of the bore.
And that based on the alignment of the protons
along the way of the bore, we know exactly where,
where a proton is because we know exactly where,
how it should be sort of spinning or wobbling or precessing.
And so here, the protons are wobbling in a difference,
in a different way than they are wobbling here
and here and here.
And so in fact, not only that within this single slice,
in every little dot in that slice there the,
the protons are wobbling in slightly different way
because of these gradient coils.
And so, additionally the, after these gradient coils
sort of encode location in our body,
we send out a radio-frequency pulse,
which transfers a little bit of energy
into a specific area in the field.
So we tell it where to go, which slice,
and based on that, it excites those protons a little bit.
And, and as it, as those protons relax,
it creates our image.
And I'll, I'll try to get into it a little bit.
Don't worry about getting too far
into the weeds of the physics of this.
Hopefully it will be okay.
So looks like he has a, have a lecture at 4:00.
I'll try to go a little bit faster.
So I'll go to the important slide.
So this is a receive coil.
So once, once your protons go back
to their normal form they, they emit some more energy
and the receive coils receive that and make an image.
By the way, if you guys need to go, go ahead and go.
These are gonna be recorded
and you can watch the rest of it at the end.
So again, after the, the RF beam is sent into the body,
the protons reflects back to their original state
and release the energy back
and that's how we get our image in.
And then the four-way transfer happens,
which is a magical thing.
And that creates our image that looks like this.
So I'm not gonna, this is not gonna be tested.
So I'm not gonna go through it.
If you guys want to read through it, you can,
but we'll just move on.
And so we'll talk about MRI safety
because that is important.
A three Tesla magnet is what we use clinically
to image our patients,
but it can also is strong enough to pick up a little car.
Unfortunately, MRI can also be dangerous
and if the wrong things are pushed into the MR room,
they get pulled in to the MR magnet,
and unfortunately they can kill people,
especially if one of these gets thrown in there.
So anything that's ferromagnetic can be acted on
by the magnet and get pulled in.
That's why we have to all change into a proper attire
before we go into the MR room.
Patients go through a detailed questionnaire
about prior metallic fragments in their body
and their eyes and documentation of medical devices
in the body is very important.
Some are MRI safe and some are not, some implants.
So here's an example where this BB in somebody's eye
is very important because this could make them go blind
if they're go into the magnet and this moves,
if they aren't blind already, that is from the BB.
And this for example is a little shard of metal
in somebody's calf, not gonna cause any problems.
The worst that could happen is it might get
a little bit warm inside the magnet.
But this is the one that we wanna make sure we don't miss.
And this is a famous actor who was here earlier,
and this was not MRI safe
so we couldn't put him in a magnet.
Oop, sorry, we're not gonna go through this.
This is a, you guys can Google Quench very loud.
More MRI safety, so the RF pulses that we sent
into the body impart a little bit of energy
in the soft tissues and cause heating.
Again, this is clinically most important in fetuses,
especially in first trimester,
who should not get heated up.
Sedated patients who can't tell us
that they're getting heated up
or they're getting burnt can also be a problem.
And any patient that has issues
with regulating their temperatures.
Magnetic fields that are higher than three Tesla
can cause actual nerve stimulation
and alter enzymes function in our bodies,
but they're not used clinically.
It's very loud in there, if any of you been in MR.
So we have to make sure we use ear protection
for our patients.
The gadolinium contrast that we use to,
for our MRI, can rarely cause something called
nephrogenic systemic fibrosis and/or organ deposition.
This is making a lot of headlines now in the brain.
This more, this happens in renally impaired patients,
the NSF, the organ deposition is felt through,
nobody understands exactly who gets more
of the brain deposition than, than others.
That's still being investigated.
And, and all these things are regulated by the FDA.
So what's MRI good for?
For soft tissue resolution.
Here's a, here's a brain of a, of a young child.
You can see the CAT scan, you can kind of see things.
You can kind of see the difference
between the different soft tissues.
Whereas here, the difference is superb.
You can see the (stammering)
the gray matter and the white matter difference.
You can see where the ventricles start and stop.
You can see the vessels.
It's, it's amazing.
In the abdomen, everything's a little bit washed out.
Whereas here you can see the cortical measure,
the differentiation of the kidney, much better.
The spleen and the liver,
all the internal structures of these organs is much better.
And of course, in the shoulder,
they're comparing x-ray to CAT scan to MRI.
You can see even the little slips inside the muscles,
much better than you can in anything else.
So soft tissue resolution, very important.
It's not very good for air.
So here are the lungs.
You can see the lungs on CAT scan here on the bottom.
You can see some of the architecture of the lungs,
whereas on the MR, you see nothing.
It's just a black void.
Same thing with cortical bone.
You can't, there's not many protons in there.
It's just black.
And unfortunately, metallic artifacts here.
There's a metallic shunt here that causes artifact.
This patient's brain is not blowing up.
It's just the artifact from the metallic implanted device.
Some of the terms we use in MRI.
Intensity, which is the relative,
as opposed to echogenicity that we use in ultrasound.
It's the relative brightness on the screen.
It's spit out by the four-way transfer
which is that magical formula.
Something is relatively hyperintense,
it is brighter than another tissue in comparison.
So here is hyperintense compared to the kidney
or hyperintense compared to the liver.
So fat is hyperintense to liver on this image.
Or isointense, which is the same as another tissue
in comparison or hypointense which is darker.
So here's lung again, which is hypointense to the liver
and the spleen next to it.
And it's all, again, and it's all relative.
In each sequence you might,
you might get out of an MRI scanner might look different.
So applications of MRI are various and,
and all new uses are always being discovered.
And for example, more recently evaluating
for fibrosis in the liver using non-invasive
without having to biopsy the liver to figure out
if the patient has a fibrosis and cirrhosis.
Also looking at liver iron deposition with MRI,
as opposed to having to biopsy the liver
to be able to see that.
And that's it.
I apologize I went over.
Again, these are all recorded.
You can go back and read, and look at them again
and go through them again.
Feel free to reach out to us if you have any questions
on particular lectures,
or if you have any questions about anything.
About the course that is.
Anybody have any questions at the moment?
Great, thank you all so much for joining
and have a great rest of your day.
- [Woman] Thank you.