What do Physicists do in

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What do Physicists do in REAL LIFE

• Many work with doctors in the field of
• Medicine

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Doctors often need to look inside our bodies
without cutting them open.
"Medical Physicists"
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

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Here is your chance to

• Find out the basics of how these scans work
• See how important physics is to modern medicine.

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X-rays
Ordinary Light

• Very little ordinary light can pass through skin.
  Its either absorbed at the surface or reflected
  back..
• To see inside we need a kind of light with
  more energy

X rays
Skin
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Taking X rays
The patient is placed in front of a source of
X RAYS
X ray Tube
A photo graphic plate is placed on the other side
of the patient
Most of the X rays pass through the patients
body.
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X-rays are absorbed by bone but can pass through
skin and soft tissue
Photographic plate
bone
X rays that are absorbed in the photographic
plate cause chemical changes. These show as
darkened areas when the plate is developed.
Soft tissue
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X-rays are also partly absorbed by some tissues
in the body this creates a more subtle picture.
Photographic plate
bone
Soft tissue
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• What part of the body do these X Rays show?

A knee
Answer
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Advantages of Basic X ray Imaging

• X rays are easy to produce
• X ray machines are relatively cheap
• In controlled doses X ray images are safe to the
  patient

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Disadvantages of X ray Imaging

• 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.

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True or False Challenge

• 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.

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CT Scans

• CT or CAT scans take X ray imaging to
• C stands for Computed
• T stands for Tomography

another level.
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In short.

• CT scanners are
• complex X ray
• machines
• attached to
• very clever
• computers
• using complicated
• mathematics to
• build up
• images of our insides.

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• 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
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• Looking end on.

X ray tube
X Rays are produced in an X ray tube, pass
through the patient and are detected by the
detector
Patient
The scanner rotates the X ray tube and detector
so the patient is scanned from all angles
X ray detector
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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.

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Advantages of CT scans

• Images are like slices
• Compared other scanners (MRI and PET) CT machines
  are quite cheap.

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Disadvantages of CT

• 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.

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True or False Challenge

• 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.

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MRI

• What do the letters stand for?
• M.. Magnetic
• R Resonance
• I. Imaging
• MRI scanners do not use X rays.

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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

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The simplest atom is
1 electron
Hydrogen
1 proton
Its nucleus contains just one proton
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In the 1940s physicists discovered that the
nuclei of some atoms have a property called
SPIN

• .Like a wobbling spinning top.

This causes the nucleus act like a tiny magnet.
N
S
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After many years of investigation physicists
found they could affect the tiny nuclear magnets
of hydrogen atoms using very strong magnets and
radio waves

• Bring in the magnets.

This high energy situation cannot be sustained
for long. Many will flip back.
.watch how the magnetic field affects the tiny
nuclear magnets
When this happens energy is released as a tiny
pulse of radio waves !!!
S
N
Note The nuclear magnets can line up in two
possible directions
A pulse of radio waves can cause some of the
nuclear magnets absorb energy and flip
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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.

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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)

Water
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Organic molecules that make up tissues
likeFATMUSCLETENDONS etc.

• contain a large number of Hydrogen atoms

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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 !
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• 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.
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• Most MRI scanners use
• magnets

Superconducting
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
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Superconducting materials only work correctly
when they are really cold..

• But not just cold like freezer temperatures.

• Can you guess how cold?

-269
Thats colder than on the surface of Pluto!
degrees Celsius
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To achieve these temperatures the superconducting
coils need to sit in a container filled with
Liquid Helium
Thankfully the patient is insulated from this
extremely low temperature whilst inside the
magnet.
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The magnet used is incredibly strong!

• 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

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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

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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

X
The magnet field produced has to be very steady
and strong
This field causes the Hydrogen nuclei in the
patients body to line up with the field
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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 onthey can make a loud banging noise.
X
More coils provide a 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..
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This information is sent to a computer which uses
it to build up an image .
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CT compared to MRI

• 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.

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View an MRI scan from any angle..
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Are MRI Scans Safe?

• 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.!

BUT
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What is the name of the condition that causes a
fear of
confined spaces

• Claustrophobia

Many claustrophobics cannot have MRI scans
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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

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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
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PET SCANNERS LOOK LIKE CT SCANNERS

• The key differences
• -NO X RAY TUBE.
• -The ring is surrounded by Gamma Ray detectors

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What are gamma rays and positrons ?
A little detour.
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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 its own ANTI
  PARTICLE
• Its.
• equivalent

Antimatter
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The antiparticle of the electron is called a
POSITRON

• When an electron and a positron meet they
  annihilate

The energy released creates 2 gamma rays
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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.
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• 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
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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.
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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.

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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.

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Brief Introduction to MEG(magnetoencephalography)

• MEG is different to all the other techniques
• It doesnt put anything into a patients body.
• No X rays/Strong Magnetic Fields/Radio
  waves/Radiotracers.
• It just measures something that is already there

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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.

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So now you know how important PHYSICS is to
MEDICINE
MRI
CT
MEG
X rays
PET