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Quantum and Nuclear

Inside Story: Physics in Medicine

Physics Narrative for 11-14 14-16

Inside Story was produced by the Institute of Physics and the Medical Research Council.

In this collection you'll find physics narrative for positron emission tomography (PET) scans, colonoscopies, magnetic resonance imaging (MRI) scans and radiotherapy, as well as a 'treat the tumour' interactive. 

Browse more resources on teaching medical physics, including worksheets, presentations and teaching guidance here.

Atomic Nucleus
Quantum and Nuclear

Magnetic Resonance Imaging

Physics Narrative for 11-14 14-16

Magnetic Resonance Imaging (MRI) uses a magnet, strong enough to pick up a car, to produce detailed images of your internal organs.

Doctors can use MRI to see which parts of the brain are active when you perform certain tasks or feel certain emotions and sensations.

How MRI Works

A large proportion of the human body is made up of fat and water, both of which contain lots of hydrogen atoms. In fact, you are made up of approximately 60% hydrogen atoms. Magnetic Resonance Imaging (MRI) works by measuring the way that these hydrogen atoms absorb and then give off electromagnetic energy.

When you have an MRI scan, you lie inside a machine that contains a powerful magnet. The nucleus of a hydrogen atom is like a tiny magnet so, by lying in line with the strong magnetic field inside the scanner, all your hydrogen nuclei line up too – just like a compass needle lining itself up with the Earth’s magnetic field.

The scanner also has several electric coils which create variations in the strength of the magnetic field at different points in your body. This means that each hydrogen nucleus experiences a slightly different magnetic field strength, which is important for detecting where exactly they are.

A pulse of radio waves is used which gives enough energy to the hydrogen nuclei for them to change direction. When the pulse is switched off the nuclei revert back to their original position and each nucleus gives off energy in the form of a radio wave. The frequency of these waves depends on the strength of the magnetic field where each nucleus is and this means that the scanner can work out the location of each nucleus.

The radio waves given off also allow the scanner to work out what type of body tissue the hydrogen nuclei are part of. This information is used to create a map of the different types of tissue in your body.

Functional Magnetic Resonance Imaging (fMRI) is a type of MRI that allows you to see which parts of your brain are active when you perform different tasks or feel certain emotions and sensations.

Brain activity requires energy and a good supply of oxygen-rich blood. The scanner can see the increase in blood flow to the most active parts of the brain because it can detect the difference between hydrogen nuclei in oxygenated blood and those in de-oxygenated blood. In this way the scanner builds-up a 3D map of which parts of the brain are working particularly hard.

fMRI mapping of the brain is used to find out how the brain carries out mental tasks and what parts of the brain are responsible for different brain disorders.

Examples of MRI Scans

You can use MRI scans to see what parts of the brain are active when your subject is doing various different things. Here are examples showing five different stimuli.

Pain

MRI scan image highlighting the areas of the brain involved in feeling pain.

The scan shows the regions of the brain that became more active when the subject's hand was heated to a painful level. Pain involves both sensation and emotion so different types of pain result in different areas of the brain being active.

Using fMRI scientists can start to understand how pain works, and how it might be possible to reduce painful experiences.

Love

 

MRI scan images highlighting the areas of the brain involved in feeling love.

Fear

 

MRI scan images highlighting the areas of the brain involved when feeling afraid.

The scans show that when your subject is frightened, a brain structure called the amygdala becomes more active.

The amygdala is responsible for generating a range of negative emotions such as sadness, anger and disgust. It becomes less active when people perform non-emotional tasks, which is why keeping yourself busy when you're sad can make you feel better.

Joy

 

MRI scan image highlighting the areas of the brain involved when feeling joyful.

Your scan shows the regions of your subject's brain that become more active when he watches his football team score a goal.

Although some of these areas are related to the feeling of joy, some may be a result of different influences, such as the anticipation of a goal being scored. Deciding what the subject should do or see to isolate an emotion is perhaps the hardest part of fMRI studies.

Smell

 

MRI scan images highlighting the areas of the brain activated by smell.

The scan shows the brain areas that are activated by smell. Smell is a complex sense and several different parts of the brain are needed to work out what a smell is, where it's coming from and whether you like it or not.

Visible Light
Quantum and Nuclear

Colonoscopy

Physics Narrative for 11-14 14-16

Colonoscopy is a technique that doctors use to look inside your large intestine - or colon - and check that everything is okay.

To do this they use an endoscope, which is a long flexible tube with a miniature camera and light at the end.

As they guide the endoscope through the colon a video screen will show the view from the camera. This allows the doctor to inspect the surface of the colon and look for any unusual features.

 

Photograph of an endoscope

How Colonoscopy Works

Your colon is the final section of your digestive system and it is here that any remaining water and nutrients are absorbed from your digested food to produce faeces or stools. The stools are then stored in the last part of your colon, your rectum, until you are able to go to the toilet and excrete them.

 

Diagram of the intestine

As they guide the endoscope through the colon a video screen will show the view from the camera. This allows the doctor to inspect the surface of the colon and look for any unusual features.

Colonoscopy uses an endoscope, which is a long flexible tube with a miniature camera and light at the end. Digital cables running through the tube carry video signals from the camera to a TV screen that gives your doctor a full colour view of your colon. Light is fed along the tube using fibre optic cables. Endoscopes also often have built-in instruments that are controlled by wires running through the tube alongside the digital cables and can be used to perform minor surgical operations during the colonoscopy.

During a colonoscopy, the flexible tube of the endoscope is inserted into your colon through your rectum. Perhaps surprisingly, this is uncomfortable rather than painful, but you will be sedated beforehand to minimise any discomfort. The obvious drawback with putting a camera into your colon to see what it looks like, is that it is normally full of partially digested food and faeces! To allow your doctor to see your colon rather than the remains of what you've eaten, you will be put on a diet of clear liquid for a couple of days, followed by a strong laxative just before the colonoscopy.

Once the endoscope has been inserted, your doctor is able to control the camera position and the amount of light as they direct it along your colon. If any suspicious looking areas are found, your doctor will use the built-in instruments to take tissue samples for later analysis.

Colonoscopies are used to look for any evidence of cancer or other diseases in the colon and any tissue samples taken during the procedure are analysed under a microscope. The early detection of diseases, including cancer, greatly increases the effectiveness of treatment.

Colonoscopy Images

Below you will see some still images taken from footage of a colonoscopy, highlighting certain features.

Feature 1

 

Image from a colonoscopy, showing benign diverticulum

The small hole you can see is the opening of a diverticulum. This is a small pouch that bulges out through a weak spot in the outer layer of the colon wall, like an inner tube that pokes through a hole in a tire. About half of all people over 50 have diverticula (plural of diverticulum) and in most cases they do not cause any problems.

Feature 2

 

Image from a colonoscopy, showing a biopsy being taken of the mildly inflamed area

In this mildly inflamed area the blood vessels are more prominent. Notice the biopsy being taken. A biopsy is where a doctor takes a sample of their patient's tissue sample, which will be sent to a lab for further tests to see if anything is wrong.

Positron
Quantum and Nuclear

PET Scans

Physics Narrative for 11-14 14-16

Positron Emission Tomography (PET) is used to look at how your body uses substances such as glucose, ammonia, water and oxygen. Seeing how these molecules move through your body, and where they are being used, allows your doctor to check for anything unusual that might suggest the presence of disease.

How PET Scanning Works

Positron Emission Tomography (PET) is used to look at how your body uses substances such as glucose, ammonia, water and oxygen. Seeing how these molecules move through your body, and where they are being used, allows your doctor to check for anything unusual that might suggest the presence of disease.

By tracking how your body uses glucose, a PET scan can produce images of cancerous tumours and help your doctor work out what treatment is best. Your body uses glucose - a type of sugar - for energy so cancerous tissue, which uses more glucose than normal body tissue, will show up as a bright area on the PET image.

If oxygen is used as the tracking molecule, PET scans can be used to image brain activity and look at blood flow in the heart to detect coronary heart disease and other heart problems.

To allow the molecules to be tracked, radioactive isotopes are attached to them before they are injected into your body. A radioactive isotope is an unstable atom with too many or too few neutrons in its nucleus. In PET the isotopes used have too few neutrons. This makes them unstable and eventually their nuclei will split, releasing positrons - positively charged electrons- in the process. When these positrons come into contact with electrons in neighbouring atoms they generate gamma rays. The PET scanner detects these gamma rays and works out where in your body they have come from, and hence the location of the molecules being tracked.

This information is then used to generate a series of images that use different colours or degrees of brightness to show the changing concentration and location of the molecule over time.

The radioactivity of the isotope decreases with time, so to get a good series of images the PET scan has to be performed as soon as possible after you've been injected.

Although having a PET scan means you are injected with a radioactive substance, the dose of radiation involved is about the same as you would be exposed to naturally over two or three years. This means that your body isn't damaged, although you wouldn't want to have lots of scans in a short period of time.

PET Scan Images

Below you will see three sets of PET scans of three people's brains.

Healthy Patient

Set of 6 PET images, showing healthy patient's brain

This scan is from a healthy 70-year-old control patient. The FDG scan looks typical for the age with a good cortical signal (that is in the outer rim of this transverse section through the brain).

Patient with Alzheimer's Disease

 

Set of 6 PET images, showing brain of patient with Alzheimer's Disease

Alzheimer's disease (AD) is a condition where the brain gradually deteriorates, leading to changes in a person's behaviour, as well as severe short-term memory loss and cognitive impairment.

AD is usually diagnosed by assessing the patient's memory and intellectual function through verbal tests. Brain imaging using PET can confirm a diagnosis as patients with Alzheimer's will typically show a reduction in glucose use in the cerebral cortex - the thin, outermost layer of the brain responsible for many complex brain functions including memory, language and consciousness.

Patient with Brain Tumour

 

Set of 6 PET images, showing brain tumour

Brain tumours are areas of tissue where the cells have mutated and are replicating uncontrollably. Mutation can occur as a result of normal brain cells coming into contact with radiation or harmful chemicals, which damage the DNA of the cells.

PET scans are useful for identifying tumours because they use more energy, and therefore glucose, than normal tissue. The FDG tracer, which is a form of glucose, occurs in higher quantities at the tumour site and this shows up as a bright area on the PET image.

Ionising Radiation
Quantum and Nuclear

Radiotherapy

Physics Narrative for 11-14 14-16

Radiotherapy is a method of treating cancerous tumours using targeted beams of radiation. The radiation is delivered by a linear accelerator, which can rotate around the patient's body to deliver the radiation from different angles.


How Radiotherapy Works

Not all cancers are the same and different tumours need different treatment plans. The three main forms of treatment are surgery, chemotherapy (using drugs) and radiotherapy (using radiation).

Radiotherapy uses precisely targeted beams of high energy photons to damage the cells of a cancerous tumour, making them unable to reproduce and spread. The high energy photon beams are created and delivered using a clinical linear accelerator which can be rotated around the patient to deliver the radiation from any direction.

Screen shot from radiotherapy planning software showing a cross section of the body and positioning of beams on the tumour.

Screen shot from radiotherapy planning software showing a cross section of the body and the levels of radiation caused by the beam placement in the above image.

The radiation can damage healthy cells as it passes through normal tissue on its way to the tumour. To reduce this damage, the radiation is fired at the tumour from a series of different directions. This ensures that the cancerous tumour will receive a full dose whilst the surrounding healthy tissue receives a much lower dose.

Plan a radiotherapy treatment to a patient with a cancerous tumour in their lung using our treat the tumour interactive.

Electromagnetic Radiation
Quantum and Nuclear

Treat the tumour

Classroom Activity for 11-14 14-16

In this activity, students use an interactive radiotherapy treatment planner for a patient with a cancerous tumour in their lung.


Apparatus and materials

Each student will require a photocopy of the instructions.

The classroom activity

  1. Target the beams of high energy photons at the tumour by repositioning the beams around the linear accelerator. Reposition the body itself using the bed controls in the top right corner.
  2. Adjust the exposure time on each beam to ensure you've exposed the tumour to enough radiation to remove it.
  3. Healthy tissue is also damaged by radiation, so you have to make sure that the tumour receives the required dose without damaging the tissue surrounding it. 

The radiation can damage healthy cells as it passes through normal tissue on its way to the tumour. Discuss with students how firing radiation from a series of different directions ensures that the cancerous tumour will receive a full dose whilst the surrounding healthy tissue receives a much lower dose.

More information about radiotherapy and linear accelerators can be found on this page

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Bed Controls

Radiotherapy complete

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