What do Physicists do in…
“REAL LIFE”
Many work with doctors
in the field of
Medicine
Doctors often need to look inside
our bodies without cutting them
open….
are essential in the development of many scanning technologies
Some you may have heard of…
X-rays…..CT scans…..MRI scans
And new ones you may not have
heard of yet….
PET scans…..MEG
Here is your chance to…
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
Find out the basics of how these scans
work
See how important physics is to modern
medicine.
X-rays
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Very little ordinary light
can pass through skin.
It’s either absorbed at the
surface or reflected
back…..
To “see” inside we need a
kind of “light” with more
energy…
Ordinary Light
X rays
Skin
Taking “X rays”
X ray
Tube
Most of the
X rays pass
through the
patient’s
body…….
The patient is
placed in front of
a source of
X RAYS
A photo
graphic
plate is
placed on
the other
side of the
patient
X-rays are absorbed by bone but
can pass through skin and soft
tissue
Photographic
plate
bone
Soft tissue
X rays that are absorbed in the photographic
plate cause chemical changes. These show as
darkened areas when the plate is developed.
X-rays are also partly absorbed by some
tissues in the body this creates a more
subtle picture.
Photographic
plate
bone
Soft tissue

What part of the body do these X Rays show?
Answer:
A knee
Advantages of Basic X ray Imaging

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X rays are easy to produce
X ray machines are relatively cheap
In controlled doses X ray images are safe
to the patient
Disadvantages of X ray Imaging
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
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In large doses X rays can be harmful to
health
Images are only “shadow prints” in one
“plane”…..no 3D information
Imaging of soft tissues and organs is not
always very detailed.
True or False Challenge…
1.
2.
3.
X rays are made of the same “stuff” as
visible light. They are both forms of
“electromagnetic radiation”.
X rays were discovered completely by
accident during a physics experiment
carried out in 1965.
X rays can damage healthy tissues.
CT Scans
CT or “CAT” scans take X ray imaging to
“C” stands for “Computed”
“T” stands for “ Tomography”
In short….
CT scanners are
complex X ray
machines
attached to
very clever
computers
using complicated
mathematics to
build up
images of our insides.
The patient is placed on a bed
The scanner (X ray machine) is the shape of a ring
The patient is slowly moved through the ring
as the scan takes place…
Looking end on….
X ray tube
Patient
X ray detector
X Rays are
produced in an
X ray tube, pass
through the
patient and are
detected by the
detector
The scanner
rotates the X ray
tube and
detector so the
patient is
scanned from all
angles
There are no photographic plates in CT scanners.
All images are created by computers using the
information they receive from the x-ray detector
ribs
spine
The image produced is like a “slice” through
the body.
Advantages of CT scans

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Images are like “slices”
Compared other scanners (MRI and PET)
CT machines are quite cheap.
Disadvantages of CT

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Still use X rays that can damage healthy
tissues (in large doses).
Imaging of soft tissues is improved but
still not always as detailed as doctors
require.
True or False Challenge…
4.
5.
6.
CT stands for Complex Tomography.
CT scans make images of your insides in slices.
Computers can now take these slices and
make a 3D picture of your insides.
With CT scans the patient receives a lower
dose of x rays than with a standard X ray
machine.
MRI
What do the letters stand for?
M……….. Magnetic
R………… Resonance
I…………. Imaging
MRI scanners do not use X rays.
MRI Explained...
Your science studies
have shown you that
your body is made up
of living cells…
Which are made up of
molecules …
Which are made up of
atoms
electron
neutron
proton
The simplest atom is…
1 electron
Hydrogen
1 proton
It’s
nucleus contains just one proton
In the 1940’s physicists discovered
that the nuclei of some atoms have
a property called “SPIN”…
….Like a wobbling spinning top.
N
S
This causes the
nucleus act like a
tiny magnet….
After many years of investigation physicists
Bring
in
the
magnets….
found
could
affect
the tiny
nuclear
This
high they
energy
situation
cannot
be sustained
magnets
ofwill
hydrogen
atoms using very
for
long.
Many
“flip”
back….
….watch how the magnetic field affects the tiny nuclear magnets
magnets
and
radioaswaves…
Whenstrong
this happens
energy is
released
a tiny pulse of
radio waves !!!
S
N
ANote:
pulse The
of radio
nuclear
waves
magnets
can cause
can line
some
upofinthe
twonuclear
possible directions
magnets absorb energy and “flip”
This tiny pulse of radio waves
that can be detected and
analysed.
The timing, and the energy of
these signals, reveals information
about the Hydrogen atoms and
what types of molecules they are
attached to.
So what has all this got to do with
looking inside your body?

What is your body mostly made of?

What is the chemical name of water?
H2O
Hydrogen in the most abundant element in your
body (approx 63% of all the atoms are H)
Organic molecules
that make up tissues like
FAT
MUSCLE
TENDONS etc.
contain a large number of Hydrogen atoms
It took physicists over 40 years to turn their
discovery of nuclear magnets into images of the
human body.
But the results are amazing…
All this from manipulating the magnetic properties of hydrogen
nuclei !
The patient is placed on a bed and then moved into
a large hollow tube.
Using an MRI Scanner…
The tube contains a very powerful magnet….
Most MRI scanners use
magnets
An electric current passes
through a massive coil made
of a special
“superconducting” material
This creates a very strong
magnet (x 20000 times
stronger than earths magnetic
field)
This may seem like a really easy way to create a strong magnet
but there is a catch……
Superconducting materials only
work correctly when they are really
cold…..
But not just cold
like freezer
temperatures….
Can you guess how cold?
That’s colder than on the surface
of Pluto!
degrees Celsius
To achieve these temperatures the
superconducting coils need to sit in
a container filled with…
Thankfully the patient is insulated from this extremely low temperature whilst
inside the magnet.
The magnet used is incredibly
strong!
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Stand 1m away with a large spanner in
your hand…. you would not be able to
hold on to it.
Patients have to remove all metallic
objects and credit cards…
Patients may have metal objects inside
their bodies…
Patients may be asked the
following questions:

Have you ever worked in the army or metal
working industry?
Metal fragments (especially in the eye) could become dislodged

Do you have a pacemaker?
If yes you cannot have an MRI scan

Do you have any dental implants
Some could become magnetised

Do you have any metal pins or staples in your
body?
Some could become magnetised and need to be checked that they will hold
in place during the scan
With the patient safety check
complete the scan can begin…
The part of the body
to be scanned is
placed in the centre
of the primary
magnet
The magnet field
produced has to be
very steady and
strong
X
This field causes the Hydrogen nuclei in the patients body
to line up with the field
Three further coils are embedded into the
tube….GRADIENT MAGNETS… these are used to
fine tune the magnetic field so particular body
parts and tissue types can be focused on.
The patient will know when
these magnets are switched
on…they can make a loud
banging noise.
More coils provide a
X
pulse of radio waves that
cause some of the “nuclear
magnets” to flip….
The machine waits and records any radio signals that
are then emitted by the patients body…..
This information is sent to a
computer which uses it to build up
an image ….
CT compared to MRI
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CT scanners scan a patient in “slices” but
the angle of the slice depends on how the
patient is positioned in the machine.
MRI scanners scan a whole section of the
body then the doctor can request to view
a slice of the patient at

any angle…
MRI scans can reveal a lot more detail.
View an MRI scan from any angle..
Are MRI Scans Safe?
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Research has failed to show up any risk to health
Patients do not feel a thing….not even a tingle!
Scans typically take 30 mins+
Staying still and putting up with clanging noises are
the only discomforts a patient has to suffer!
a further group of people may find it
impossible to have an MRI scan….!
What is the name of the condition
that causes a fear of…
“Claustrophobia”
Many claustrophobics cannot have MRI scans
True or False Challenge?
It is dangerous for a patient to stay in an
MRI scanner for too long
8. Superconducting magnets are cheap to
make and use.
9. Claustrophobics are not allowed to have
CT scans
7.
Introductions to PET
(positron emission tomography)
“snapshot” images are useful
but doctors sometimes need “real time”
pictures of how parts of your body are
functioning…
e.g. How your heart is
functioning.
Moving images can be achieved
with MRI but PET scanning can
give excellent results…
PET SCANNERS LOOK LIKE CT SCANNERS…
The key
differences:
-NO X RAY TUBE.
-The ring is
surrounded by
“Gamma Ray”
detectors
What are “gamma rays” and
“positrons” ?
A little detour….
You will have heard of…
Electrons
Protons
Neutrons
These are the building blocks of atoms.
Physicists have discovered a whole host of other particles
that exist !!!
AND ASWELL: Every particle has it’s own ANTI PARTICLE…
Its….
equivalent
The antiparticle of the electron is
called a…
When an electron and a positron meet they
annihilate…
The energy released creates 2
gamma rays
PET scan patients are injected with a
specially created substance called a
“RADIOTRACER”….
Usually a “Radioactive” type
of glucose.
The radiotracer is a source of
positrons which leads to the
production of gamma rays…
INSIDE THE PATIENTS BODY!
These pass through the patients
body and are picked up by the
scanner.
Looking at the scanner: end on….
The radio tracer
produces positrons
which annihilate
with electrons in
the patients body
producing pairs of
gamma rays.
Patient
The energy and
position of all the
gamma rays are
recorded and
turned into an
image by a
computer.
Ring of gamma
ray detectors
The radiotracer concentrates itself in
certain tissue types…
This glucose
type
radiotracer has
concentrated
itself in high
glucose using
cells like the
brain, kidneys
and cancer
cells.
PET Scans are very expensive…
The biggest cost is in the production of the
RADIOTRACERS.
The hospital needs to have access to a
“CYCLOTRON” to create them
(several million euro to buy one!)
Radiotracers have to be used straight after they are produced….they
cannot be stored.
True or False?
10. PET scanning poses no risk to patient
health. Doctors can use them as often as
they like.
11. “Antimatter” is just an idea invented by
science fiction writers.
12. Gamma rays are also a form of
“electromagnetic radiation” like light and X
rays.
Brief Introduction to MEG
(magnetoencephalography)
MEG is different to all the other techniques…
It doesn’t put anything into a patients body….
No X rays/Strong Magnetic Fields/Radio
waves/Radiotracers.
It just measures something that is
already there…
Your body is full of tiny electric
currents!
These tiny currents produce tiny magnetic fields
MEG is able to measure some of these.
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MEG is mostly used to
image brain activity.
MEG scanners measure
tiny magnetic fields
produced by electrical
brain activity.
These fields are so weak
(10,000 million times
weaker that the earths
magnetic field) that the
scanner needs to be in a
specially shielded room.
So now you know how important
PHYSICS is to MEDICINE