that can get out and cause a stroke or other
X-ray and CT/MRI are magnificent imaging techniques
that give us very detailed pictures of the
inside of the body. So let’s look at each
of the kinds of x-ray or radiation techniques
used: the plain x-ray, the CAT scan or CT
scan, the fluoroscopy sometimes with angiography
– with an invasive test – or the lung
scan using nuclear-medicine techniques. Let’s
look at each of these.
So let’s look at the plain x-ray. This uses
x-rays – electromagnetic radiation – that
penetrate the body. And in fact the first
x-rays were done here in Germany by a man
called Roentgen. And that’s why we talk
about Roentgen rays or x-rays. It shows the
internal structure of the body. The x-ray
generator produces a similar and smooth beam
of x-rays that projects towards the body.
Organs and bones absorb certain amount of
the x-rays and lungs and so forth where air
absorbs less. And then there’s a photographic
plate or a screen that’s very sensitive
to the x-rays behind and it gives us a two-dimensional
image of the body’s internal structures.
You can see on the example that there is the
heart and the lungs and the ribs.
The CAT scan is a more sophisticated x-ray
machine. It uses the same form of electromagnetic
radiation but it does it in a three-dimensional
manner. And also using a computer program
reconstructs two and even eventually three-dimensional
images. So you can see here what’s going
on. There are images. X-rays are given from
different angles and they produce a cross-sectional
or so-called tomographic image. And these
virtual slices can be put together even to
show us a three-dimensional reconstruction.
This is very good for looking also at the
soft tissues. It doesn’t just show the bones.
There are very specific areas inside the body
that can be displayed such as the various
heart chambers. It shows, at times, the extent
of occlusion in coronary arteries when dye
is administered. So in a sense it’s a sort
of non-invasive technique at angiography.
The patient’s injected with an intravenous iodine
dye and the heart is scanned using a very high speed
CT scanner. And we can actually image the
blood vessels in the heart, the arteries. And here is
a picture of an actual CT scanner.
Fluoroscopy is very much like the plain x-ray
except that we’re looking at a fluoroscope
and we can actually see the heart moving and
sometimes even the blood vessels pulsating
with the fluoroscope. We use the fluoroscope
when we’re also doing invasive testing so
that we can guide the catheters into the right
place to inject dye so that we can see pictures,
for example, of the coronary arteries. Fluoroscopy
uses the same x-rays as I said before and
it gives us moving images of the body’s
With angiography – we’ll mention that
later – that’s an invasive technique where
catheters are placed into the body and dye
is injected directly into various arteries.
And we can visualise the channel to see if
there are obstructions. This can be done both
for the arteries and for the veins when we
want to see if there’s obstruction in either
of those areas and we can also see if there
is obstruction within the heart chambers.
The lung scan consists of an injection as
well as inhalation of radioactivity. What
we do first is to have the patient take a
deep breath. And in that breath there is radioactive
xenon gas and it shows us the distribution
of the air in the lung. Then a different radioactive
substance – there’s a variety of different
ones, one of the commonest is radioactive
technetium – is attached to albumin molecules.
And it’s injected intravenously and it goes
where the blood flow goes in the lung so that
we get a picture of where the air is with
the xenon inhalation, so-called ventilation
scan. We get a picture of where the blood
itself is going in the perfusion scan below.
And we make a comparison. In patients with
clots in the lung – pulmonary embolism – such
as this example, the aeration is normal but
there are multiple areas where the blood flow
is abnormal because there’s obstruction
in the pulmonary circulation from clots.