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….

Some you may have heard of…X-rays…..CT scans…..MRI

scansAnd new ones you may not have

heard of yet….PET scans…..MEG

are essential in the development of many scanning technologies

Here is your chance to…

Find out the basics of how these scans work

See how important physics is to modern medicine.

X-rays 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…

Skin

Ordinary Light

X rays

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 patient’s body…….

X-rays are absorbed by bone but can pass through skin and

soft tissue

bone

Soft tissue

Photographic

plate

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.

bone

Soft tissue

Photographic

plate

What part of the body do these X Rays show?

Answer:

A knee

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

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.

True or False Challenge…1. X rays are made of the same “stuff”

as visible light. They are both forms of “electromagnetic radiation”.

2. X rays were discovered completely by accident during a physics experiment carried out in 1965.

3. X rays can damage healthy tissues.

CT ScansCT or “CAT” scans take X ray imaging

to

“C” stands for “Computed”

“T” stands for “ Tomography”

In short….CT scanners are complex X ray machinesattached to very clever computersusing complicated mathematics to build up images of our insides.

The patient is placed on a bedThe 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

X ray detector

Patient

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

The image produced is like a “slice” through the body.

ribs

spine

Advantages of CT scans

Images are like “slices” Compared other scanners (MRI and

PET) CT machines are quite cheap.

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.

True or False Challenge…

4. CT stands for Complex Tomography.

5. CT scans make images of your insides in slices. Computers can now take these slices and make a 3D picture of your insides.

6. 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…

Hydrogen1 electron

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.

This causes the nucleus act like a tiny magnet….

N

S

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….

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”

This high energy situation cannot be sustained for long. Many will “flip” back….When this happens energy is released as a tiny

pulse of radio waves !!!

….watch how the magnetic field affects the tiny nuclear magnets

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?

H2OHydrogen in the most abundant element in your body (approx 63% of all the atoms are

H)

Organic molecules that make up tissues like

FATMUSCLE

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.

The tube contains a very powerful magnet….

Using an MRI Scanner…

Most MRI scanners use

magnetsAn 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?

degrees CelsiusThat’s colder than on the surface of Pluto!

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!

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 implantsSome 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

XThe 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

X

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 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

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?

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?

7. 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

“snapshot” images are usefulbut 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…

Introductions to PET(positron emission tomography)

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…ElectronsProtons

NeutronsThese 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….

Ring of gamma ray detectors

Patient

The radio tracer produces positrons which annihilate with electrons in the patients body producing pairs of gamma rays.

The energy and position of all the gamma rays are recorded and turned into an image by a computer.

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.

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