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so I'd like to welcome you to our
radiology course we're going to begin
this course by discussing some
background of radiology and how it all
began and then I'd like to give you some
basics of the of an introduction to
imaging we'll talk about some basic
things that you'll see throughout the
course including the densities that are
seen radiographically and we'll give you
an introduction about radiographs and
about CTS as well so radiology was
discovered by Wilhelm Rankin in 1895 in
Germany he was actually studying the
effects of a vacuum tube equipment when
an electrical charge is passed through
and he noticed that a cardboard box
painted with the fluorescent material
glowed when it was placed adjacent to a
cathode ray tube he realized that this
was due to a type of ray which he called
an x-ray so there are four basic
radiological densities they are air fat
fluid and calcium these are the four
that you'll see over and over again in
all of the different types of imaging
modalities that you'll encounter there's
also a fifth type of density which is
metallic and we see this more and more
frequently as patients have multiple
metallic objects placed within them such
as prostheses and valves so conventional
radiography is also called an x-ray and
it's produced by ionizing radiation you
see two examples here of a normal chest
x-ray and a normal abdominal radiograph
or an abdominal x-ray these are also
called plain films so there are multiple
terms that really signified the same
thing a radiograph a plain film or an
x-ray are really all the same thing
there are two basic principles of
conventional radiography there's what's
called summation of shadows so that
means that images are created by
multiple overlapping tissue densities
and the density of the object increases
as you have more overlap there's also
the silhouette sign which will come up
over and over again and that just means
that the edges of an object are seen it
only if it interfaces with an object of
a different density so as you can see
here this area appears very dense and
that's because you have overlapping of
multi
objects or a summation of shadows we
have the thoracic spine we have the
heart and we have the mediastinal
structures all overlapping with each
other here you can also see there's
actually a little bit difficult to
differentiate here between something
that's going on in the lung and the
right heart border and this is an
example of the silhouette sign so
whatever is going on here which is
actually an area of pneumonia is
silhouetting the right heart border so
we don't see it any longer if you look
at the left heart border that actually
interfaces with normal lung and so we do
see this well because it's two objects
of different densities orthotic or THOG
'''l imaging is actually very important
when it comes to radiographs radiographs
really should be obtained in at least
two different projections whenever
possible because what you're doing is
you're looking at a three-dimensional
structure and you're using a
two-dimensional image to take a look at
it so if you don't perform it in two
different views it's hard for you to
identify the location of an abnormality
so let's take a look at an example here
we see what appears to be a metallic
column within the midline of the chest
on this single 2d frontal view so where
in the body is this located is this
anterior to the heart or is this
posterior to the heart it's actually
very difficult or impossible to say just
based on this single 2d image so what we
need is a lateral image to show us the
exact position these two images together
will tell us exactly where this object
is located so it helps us identify that
this object is located posterior lean
and this is actually a spinal stimulator
so it's very important whenever you do
any kind of plain film imaging to do at
least two different views whenever
possible so how about computer
tomography or CT this is again known as
a CT scan or a cat scan the official
term is computed tomography this
actually uses higher levels of ionizing
radiation than a radiograph does and a
CT image is created and it's actually a
matrix made up of thousands of different
pixels pixels are measured in Hounsfield
units so this is again an
Courtin concepts that may come up over
and over again with CT scans Hounsfield
units are based on how much x-ray beam
is actually absorbed by the object and
it reflects the density of that object
so it ranges from a scale of negative
1,000 to positive one thousand air has
the least Hounsfield units it measures
about negative one thousand Hounsfield
units bone is close to one of the
highest Hounsfield units so it measures
anywhere between four and six hundred
Hounsfield units and again this is
somewhat of a range these aren't exact
numbers and they can vary a little bit
by individual this is an example of what
a CT scanner looks like so you can see
that the patient will lie right here and
this table actually goes inside the bore
this rotates and creates an image CT
scans can be evaluated using multiple
different window levels so CT scans are
obtained in just one projection so we
have an axial image right here which is
a single slice cut through the body and
it's performed it's performed only in
one set of windows however
post-processing allows you to evaluate
this in multiple other window levels so
we can see here this is called a long
window because you can see the lungs
very well this one here is called a bone
window because you can see the bones
very well and this is all done actually
by the radiologist at their own
workstation so it involves no additional
radiation to the patient
CTS can also be evaluated in multiple
planes so CT images are post processed
again in two different planes which
doesn't require react juez ition of
different images so the axial is the
plane that is most commonly done and
that is looking at the patient from
their feet up to their head so the
images that we were just looking at are
axial CT images sagittal images actually
look at the patient from one side to the
other and I'll show you an example
coronal images or the third different
plane is looking at the patient from the
front to the back so let's take a look
at an example of sagittal and coronal
images so this here is an example of a
sagittal image you can see that it's
it's looking at the patient from one
side to the other
this is anterior
and this is actually the sternum this
here is posterior so you can see the
thoracic vertebrae and you can see the
spinous processes on this side we have a
coronal image so looking at the patient
from front to back you can see here both
lungs you can see the heart right here
and you can see a portion of the liver
by convention this side of the CT scan
is always the right side of the patient
and this side is always the left side of
the patient so again it's as if you are
looking at the patient and the patient
is facing you
CTS can be performed with or without
intravenous contrast contrast is
iodinate it's Anaya donated solution and
it's administered really for vascular
evaluation or any structures that
contain vascularity it's helpful in
determining enhancement and
differentiating between different
adjacent structures so it's almost like
the silhouette science seen in
radiography if you take a look at this
non contrast image of the chest you can
see that the heart is pretty much of
equal density all throughout it's very
difficult to identify the different
chambers of the heart however if you
look at this contrast enhanced
examination right adjacent to it at the
same level you can see that now we can
identify the different chambers of the
heart very easily because in between the
chambers of the heart you have the walls
of each chamber which help you
differentiate between a contrast filled
structure and a structure that doesn't
fill with contrast
so intravenous contrast is a low ionic
low osmolar solution it contains high
levels of iodine which is what's
absorbed by the x-rays and that's what
makes the image appear white it's
excreted by the kidneys and because of
that there's a contraindication in
patients who have renal failure because
it can cause acute tubular necrosis
which may or may not be reversible
patients may have an allergy to contra
CT contrast and the symptoms can range
quite significantly from hives to
anaphylaxis
so if a patient reports an allergy to CT
contrast than CT contrast cannot be
administered in that patient usually
even with Medi
patience on board depending on the level
of allergy that they've had in the past
oral contrast is another way of
performing a c-team and this actually
helps distend and define the bowel
what's most commonly used is dilute
barium sulfate and the patient drinks
this solution approximately a thousand
to 1500 milliliters of it orally and
it's usually performed about it's
usually given about 60 to 120 minutes
prior to the examination so this patient
drinks the solution and then they wait
for approximately two hours or so and
then the exam is performed and this
allows the oral solution to get down
into the small and large bowel
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you