X-Rays and things like them
So, you want to know more about X-Rays and things eh?
Well, here are the basics. We could get very technical here but
you will be pleased to know I will try to be as brief as I can.
First the simple X-Ray. An X-ray is basically the same
as any photo or holiday snap but it uses a different sort of `light`
to make a picture. Ordinary light as we all know bounces off things
like walls, floors and bodies and does not pass through them.
If it did, we would be able to see through everyone. X-Rays are
a special sort of `light` that instead of getting blocked by solid
objects like our bodies actually passes right through them.
When an X-Ray is taken, a machine that make the X-Ray
beam is put on one side of the body and a film that is sensitive
to X-Rays is put on the other. The X-Ray is shone from one side
of the body, through it and onto the film on the other side. Where
the body is soft, such as in the tissuey bits, the X-Rays get
through easily so more of them go through the body onto the film
behind. Where the body is harder and thicker, such as in the bones,
the X-Rays get through less so less reach the film behind. When
the film is developed, the parts where less of the X-Ray got through
show up and we get, for example, an outline of the bones.
There is, of course, a catch to X-Rays...they are a
form of radiation so there is a very slight risk associated with
them. X-Ray radiation can increase the risk of cancer but only
in very large doses. There is lots of X-Ray radiation around us
all the time however and so the extra risk from medical X-Rays
is very small indeed.
One important point should be mentioned here though.
The dose of X-Rays is very different depending on what is being
looked at. When a chest X-Ray is done, we are mainly looking at
the tissues in the lungs so a very tiny dose is needed, one that
you would get naturally over a few days anyway. If, however, an
X-Ray of the back is needed many many many more X-Rays are needed
to get through the thick bones of the back to get a good picture.
The radiation dose is far higher. (Although still very low generally).
It is for this reason that your Doctor may be reluctant to order
an X-Ray if you have backache. (besides which, an X-ray is rarely
useful in backache as the cause usually will not show up.
Now a word about Scanners. These are the machines
that you will all have seen on TV where someone lies down on a
moving table and goes into a tunnel like thing. How does one of
these work I can see you all asking? Well, actually, the principle
is very simple. Imagine shining a torch at someone that makes
a long straight beam of light ( like a laser beam... a long thin
straight beam ) Now imagine if the torch was an X-Ray Torch making
a beam of X-Rays.
If you shone the torch through a soft bit of the body
like a muscle, most of the `light` would come out of the other
side. If you shone it through a thick bit like bone, not much
of it would come out. You would know what was inside by how strong
the beam coming out of the other side was.
If you knew the right information you could work out
how much bone and how much tissue (or whatever else) was blocking
the route of your beam. Here is the clever bit. In a CT scanner,
the beam is rotated around a complete circle all the way around
the body. The computer in the machine therefore knows how much
bone or tissue there is at any point in the body. it can use this
information to produce a picture of a `slice` of the body. The
picture not only can show up bones, but other different tissues
as well.
MRI scanners are a more advanced way of looking at
the body and produce clearer images than CT scans (An example
is the one above). No X-Rays are used in MRI scanners. Magnetic
Resonance Imaging uses very powerful magnets to produce strong
magnetic fields. The magnetic and electrical fields in the scanner
are rapidly changed and this causes the protons within hydrogen
atoms, particularly in water molecules to change direction. They
change back after the forces are released and in so doing release
small amounts of energy which can be detected. Powerful computers
use this information to create an image.
BACK TO MANOR
MAGAZINE MAINPAGE