Textbook a5

8/3/2019 Textbook a5

1/40

www.teachingmedicalphysics.org.uk 1

Contents

History 2

Radiation Physics 5X-radiography 6CT 7Nuclear Medicine 9PET 11

Radiotherapy 13Radiation Protection 16

Ultrasound 19Ultrasound imaging 19Doppler Ultrasound 21

Optical Methods 23

Endoscopy 23Pulse Oximetry 25Laser Surgery 26

MRI (magnetic resonance imaging) 28

ECG (electrocardiogram) 31

Bioengineering 32Pacemakers 32Medical Engineering 33Cochlear Implants 34

The Future 37

Glossary 38

Acknowledgements 40


2/40

What is Medical Physics?

Medical physics is the application of physics to medicine.A large part of medical physics concerns the use ofradiation to examine and treat the body. Other areas

include medical ultrasound, endoscopy and MRI scans.

History

Most people think that Medical Physics started in 1895 whenWilhelm Roentgen discovered x-rays but, in practice, physicshas been used to investigate the body for much longer thanthis.

Hippocrates (460-377 BC), the Father of Medicine, mayhave been the first medical physicist. Over two thousandyears ago, he wanted to know where an infection was on apatients back. He smeared mud over the patients back ashe knew that infected tissue is warmer and would thereforedry the mud faster.

Technology has improvedsince then, and modernthermography, whichlooks at heat comingfrom the body using aninfrared camera, is verydifferent fromHippocrates' methods.



3/40

When doctors wanted to be able to see inside the stomachand intestines, they first simply used a thin tube with lightprovided by a candle. In 1868 a metal tube was passed down

the throat into the stomach. This was an early prototype ofan endoscope. Large early models were tested on swordswallowers, and were very intimidating, with one manquoted as saying 'I'll swallow a sword, but I'll be damned ifIll swallow a trumpet'. Modern endoscopes are smaller andmore flexible, making endosopy a less unpleasantexamination.

In the future, we will use camera pills that can beswallowed and travel all the way through the digestivesystem without any discomfort.

The most common medical imaging examination today is anx-ray, or radiograph. X-rays were discovered in 1895 byWilhelm Roentgen, who was passing an electric current

through a glass tube with a vacuum inside, when he noticeda screen nearby start to glow. He realised that someinvisible rays from the tube were causing the glow, andcalled them x-rays as he didn't know what they were. He setto work, trying to find out more about these strange rays.

His wife became worried that he wasspending so much time in his lab, andwasn't eating properly or talking toanyone. She finally persuaded him totell her what he was working on, andhe took her into the lab. She tried ohis equipment by putting her handthe x-ray beam for fifteen minutes,and saw an image of her hand appe

on film behind it. This was the firstmedical x-ray image. Roentgen was

utin

ar



4/40


awarded the first ever Nobel prize in Physics in 1901.

Soon after Roentgens discovery, HenriBecquerel, a

ed

it

arie Curie, along with her husband Pierre, continued the

eland,

or a while radiation was hugely fashionable, with people

of

es

a

Frenchman, was experimenting with salts that fluorescwhen exposed to sunlight to see if they would emit x-rays.One cloudy day he left a photographic plate and a uraniumcompund in a drawer, and when he developed the film hefound that it had been exposed to something, even thoughhadnt seen any light. He realised that uranium gave offinvisible rays that could ionise atoms and blacken film. He

called this radioactivity.

Mresearch into radioactive materials, discovering newradioactive elements Polonium (named after her homPoland) and Radium. Bequerel and the Curies shared a Nobelprize for their work.

Fputting radium in water and thorium in toothpaste. Thishealth craze was dangerous though, and ill effects weresoon noticed. Thegirls who painted radium onto the dialswatches developed thoat and mouth cancers from lickingtheir brushes, while people using radioactive productssuffered symptoms such as burns, hair loss, bone diseas

and various types of cancer. Marie Curie herself died fromblood disease linked to radiation exposure (Pierre, thoughsuffering from radiation sickness, died when run over by ahorse and cart) .


5/40

By this time, it had beenrealised that, althoughharmful in large doses, small

amounts of radiation could beused to treatdiseases such ascancer. The radioisotopecobalt-60 became used inradiotherapy machines (seeleft) and today radiotherapyuses high energy x-ray beams

to treat tumours.

Radiation Physics

Ionising radiation can be either alpha or beta particles, or

high energyelectromagnetic waveswith enough energy tocompletely remove an electron from an atom.

How does radiation affect the body?

In large doses, ionising radiationcan be dangerous and cancause burns to the skin and sickness. In medical imagingradiation doses are too low to cause serious damage, though

there are still risks. Radiation can damage the DNA in cells.Sometime the cells can repair the damage, thoughsometimes they cannot and die. This fact is useful in thetreatment of cancer where radiotherapy is used to kill thecells in a tumour. Another problem is that radiation canchange the DNA without the cell dying. This is called amutation, and mutations can lead to the person being more

likely to develop cancer later in life, or can be passed on totheir children, sometimes leading to genetic abnormalities.



6/40

X-Radiography

X-ray radiography is one of the most commonly usedmethods of diagnosis. It can be used to examine broken orfractured bones, teeth, the digestive system, the lungs andto detect breast cancer.

X-rays are produced when electrons hit a metal, which inhospital x-ray tubes, is usually tungsten. The x-rays thenpass through the body and onto either a film cassette or

digital detector (like in a digital camera).

Structures in the body likebones are very dense andcontain elements such ascalcium that have a highatomic number. This makesbone absorb a high proportion

of the x-rays. Soft tissues likefat and muscle allow more x-rays to pass though. The bodycasts an x-ray shadow onto thefilm. Where the x-rays havepassed though bone, the film isless exposed so it looks white;

where they have not passedthough anything the film isexposed and turns black; and where the x-rays have passedthrough soft tissues the film has different levels of grey.



7/40

In order to make some parts of the body show up better,contrast media with a high atomic number can be used.This can be a 'barium meal', where the patient drinks a

liquid containing barium (atomic number 56) which makesthe digestive tract show up clearly on x-rays, or the patientcan have an injection ofiodine (atomic number 53) whichmakes the blood vessels stand out (this is calledangiography).

CT (computed tomography)A CT scan (sometimes called computed axial tomography, ora CAT scan) also uses x-rays.

In a CT scan the patient lieson a table and is movedthough a doughnut-shaped

machine. It creates imagesthat are slices through thepatient.

It does this by moving the x-ray tube and detector in acircle taking x-ray images ofthe slice from all anglesaround the body.

A computer then processesthese images to produce across sectional image (apicture of a slice through thebody).



8/40

CT scans are useful as they can show a range of verydifferent tissue types clearly: lung tissue, bone, soft tissueand blood vessels.

By adding together CT s3-D images can begenerated.

lices,

They are often used to planradiotherapy treatments.

CT is useful for diagnosing internal inuries in trauma victims.

Because a scan takes only a couple of minutes it can findproblems quickly and save their lives.

One problem with x-ray CT is the radiation dose to thepatient. A scan of the abdomen gives a dose of 10mSv,which is equivalent to the natural background radiationexposure over 4 years. This is about 100 times more than a

standard chest x-ray.



9/40

Nuclear Medicine

Nuclear medicine uses radioactive isotopes (radioisotopes)to image the body. X-ray images show only the structure ofthe body, so they can be used to see things like brokenbones and some tumours. Unlike x-ray images, nuclearmedicine can show the function of the body. It follows whathappens to certain chemicals so it can be used to see if anorgan is doing its job properly. The chemicals, called

tracers, are 'labelled' with a radioactive isotope and theirpath followed through the body.

The radioisotopes areproduced in generatorswhere isotopes with longhalf-lives (e.g.molybdenum-99, half-life67 hours) decay toisotopes with shorterlives (e.g. technetium-99m, half-life 6 hours).

The shorter half-lives are necessary so that the radioactivityof the patient does not remain much above its normal

background level for longer than necessary.


The isotope with theshorter half life is drawnout of the generator in asolution and can be madeinto a range of differentdrugs(radiopharmaceuticals) thatare absorbed by different


10/40

parts of the body. The radiopharmaceutical is drawn up intoa syringe shielded with lead and its dose checked before itis injected into the patient.

sotope

The gamma rays given offby the radioisotope aredetected by a gamma-camera (a detector thattakes images with gammarays) which is connected to

a computer and gives animage of where the iis in the patient. Theimage shows where thedrug is absorbed.

If several pictures are takenover a period of time it canalso show how quickly theisotope is absorbed.

These three images show thebuild up of a tracer in the

kidneys over time. We can tellthat the left kidney isblocked, as the tracer hasntbeen able to reach it.



11/40

PET (Positron Emission Tomography)

Positron Emission Tomography (PET) scanning uses beta+

emitting isotopes.

The isotope decays emitting a positron (which is a positiveelectron, also called a beta+ particle, and is a particle ofantimatter). The positron can only travel about 1mm before

losing its energy and slowing down.When it slows down enough, it will

meet a negative electron from anearby atom, and they will'annihilate', leaving no particles.Their energy is converted into twogamma rays which travel in oppositedirections so that momentum isconserved.


A PET scanner has a ring of detectorsso that both gamma rays are seen,and is connected to a computer

which can work out where the gamma rays came from andproduces an image.

Not all hospitals

have PET scannersas they need large,expensive machinescalled cyclotronsnearby to producethe positron-emitting isotopes.The isotopes have a

shorter half-lifethan the gamma emitters used in traditional nuclear


12/40

medicine (e.g. Carbon-11, which has a half-life of20.5mins).

PET imaging is often used todetect tumours. As cancers aregrowing quickly they need a largesupply of energy, which they getfrom glucose. A chemical calledfluoxyglucose can be labelled withpositron emitting fluorine-15,

which then collects in the tumourand shows up as a bright spot inthe PET scan (like in the rib in thepicture on the right).

Some PET scanners now have a CTscanner next to them so both types ofscan can be done at the same time. Thiscan easily be done as both types ofscanner are shaped.

This image is a combined PET/CT image.The excellent contrast from the PETscan, in which the brain and bladdershow up as bright red, is combined withthe anatomical detail from the CT(shown in grey).



13/40

Radiotherapy

Radiation is not just used for diagnosis, but for treating

cancer as well. This is called radiotherapy.

Radiotherapy uses the fact that ionising radiation damagescells, and high enough doses can kill them. The cells incancerous tissue divide very rapidly. This makes them moresusceptible to damage by radiation than healthy cells, sothere is a higher chance that they will be killed. Even so,care has to be taken to ensure that only the malignantcancer cells, and not the surrounding healthy tissue, receivea high dose.

This is done bymounting thesystem on a ring sit can rotate

around thepatient, with thetumour at thecentre of therotation. In thisway the tumourgets a higher dose

of radiation than the surrounding healthy tissue.

o

Originally, radiotherapy machines consisted of a cobalt-60source which emitted gamma rays which irradiated thetumour. Modern hospitals use linear accelerators (linacs forshort) instead to produce very high energy x-ray beams,with a higher energy than the Cobalt-60 gamma rays. In theUK, medical physicists are required by law to calibrate the

linacs to ensure that the best possible treatment is given.Each treatment requires careful planning. This involves



14/40

deciding which directions to irradiate the tumour from,what dose to give and, in new machines, what shape regionto expose.

The size, shape and locationof the tumour are worked outusing CT or MRI scans. Isodosecurves, which join points thatwill receive the same dose,are drawn onto this CT scan.

Brachytherapy

In Brachytherapy (meaning short-distance therapy),radioactive material is inserted into the body, inside or nearto the tumour. This means the tumour receives a high dosewhile the surrounding tissues have a smaller exposure.

Here, tiny pellets of radioactiveiodine-125 have been implantedinto the prostate gland.

These pellets will not be removed,but have a fairly short radioactive

half-life so that after a while theywill become inactive.



15/40

The Gamma Knife

The gamma knife is not reallya knife, but a way ofperforming brain surgerywithout cutting through theskin, muscle or skull. It uses201 radioactive cobalt-60sources to irradiate the bCobalt-60 emits gamma

and has a half-life of 5.26years.

rain.rays

The first stage in treatment is to fit a metal frame to theskull, which is done using four screws under localanaesthetic. The rigid frame allows the radiotherapy to beperformed very precisely.

Then, the treatment is planned using CT or MRI images, sothat the sources are correctly targeted, to irradiate thetumour and avoid healthy tissue, especially sensitive regionsaround the eye and cochlea.

The Cobalt-60 sources are positioned in a hemisphere. Thepatients head, held in the frame, is held inside a helmet

with 201 holes to precisely target the radiation. Whentreatment starts, the patients head is moved inside theunit.

The gamma knife is used to treat benign and malignanttumours, blood vessel malformations, some pain conditionsand some movement and psychiatric disorders. In 2006,there were three in the UK (two in London and one inSheffield).



16/40


17/40


How can we protect ourselves?

There are many ways to reduce the dangers from radiation.

The first is only to use it when necessary. Before peoplerealised it was dangerous, shoe shops used to x-ray peoplesfeet to check that new shoes fitted properly. This no longerhappens as the benefit did not justify the risk. However,the benefits of seeing where a bone is broken so it can besafely and properly mended are considered worth the smallextra risk.

Every x-ray examination has a strict controls about themaximum radiation dose a patient can be given, and thepatient can be covered with lead-rubber shield to protectthe parts of them not being examined from the radiation.This is especially used to protect reproductive organs sothere is less risk of a mutation being passed on.

People such as radiographers and nurses who work withradiation every day will leave the room or stand behind alead shield when a procedure takes place, as the risk ofdeveloping problems due to radiation exposure increaseswith total dose. They also wear film badges which aredeveloped regularly to check the dose they have recieved.


18/40

What jobs do medical physicists do?

Medical physicists work in many areas of the hospital.They are often responsible for maintaining andcalibrating sophisticated equipment like MRI scannersand linear accelerators. They may develop new ways ofusing equipment to diagnose and treat unusualconditions. They may also be responsible for hospitalcomputer systems. In general, they ensure that all thehigh-tech equipment needed in a modern hospital isworking well so patients can be diagnosed safely andquickly.

Many medical physicists also work in research inuniversities, industry and hospitals, improving existingtechniques and developing completely new ones. People

such as Sir Godfrey Hounsfield and Sir Peter Mansfieldhave won Nobel prizes for their work in CT and MRIrespectively.

Who does medical physics?

Roughly half of medical physicists are women and halfare men. If youre considering a career in medicine,physics or engineering, then medical physics may appealto you.

Medical physicists use a wide range of skills includingwriting computer programs, inventing new equipment,

and working with patients.



19/40

Ultrasound

Ultrasound imaging

Ultrasound uses sound waves with frequencies between1 and 10MHz to look inside the body. These frequencies aretoo high to be heard by humans. The ultrasound waves, likeall waves, can be reflected, refracted or transmitted at

boundaries. It is the reflections, or echoes, which are usedto produce ultrasound images.


A gel is used so the probe makesgood contact with the skin. It sout pulses of ultrasound, andmeasures the time taken to detect

the echo and the strength of thesignal. The time taken indicateshow deep in the tissue theultrasound wave is being reflected.

ends

kidney stones, which

Ultrasound imaging isparticularly good atdetecting cysts, whichare pockets of fluid, inthe liver, glands andovaries and breasts,and can be used toidentify gallstones and


20/40

are deposits of minerals. Large blood vessels also show upclearly.

Ultrasound is commonly used during pregnancy to check thedevelopment of the foetus. It can show the size of thefoetus which indicates how far along the pregnancy is, checkthat the heart is beating and identify problems.

It is thought to be safe as it doesnt use ionising radiation.

Computers can now g3-D ultrasound images, an4-D (3-D over time)ultrasound scans can bemade into videos forparents.

enerated

This image is processed toshow the skin. This is calledsurface rendering.



21/40

Doppler Ultrasound

The Doppler effect is the change in the frequency of asound due to the person listening moving relative to thesource of the sound. If you move towards a source (or standstill and it moves towards you) the pitch, or frequency ofthe sound, increases. Likewise, if you move away from thesource, the pitch of the sound decreases and it soundslower. This can be easily noticed in the pitch of anambulance siren as it gets closer, passes you and thenmoves away.

The Doppler effect is used in medicine to study blood flow.It can tell you if blood is moving towards or away from theprobe.

This is a Doppler ultasound probe. It

is being used to examine blood flowin the radial artery, the same onethat you would use to measure yourpulse.


There is some gel on the skin tomake sure the probe makes a goodcontact so the sound can pass easilyinto the body.

probe

gel


22/40

This is the Doppler ultrasound signal measured from ahealthy artery. When the heart beats it pushes blood at a

velocity of over 100cm/s away from the probe.

The information can be colour coded and combined withconventional ultrasound images, which is particularly usefulin diagnosing blockages in blood vessels.

This combined image showsthe blood is all flowing inthe same direction. Thisindicates that the bloodvessel is healthy.

In this image some blood is

moving away from theprobe and some bloodtowards it. This is tflow, like rapids in a river,and is caused by a blockagein the blood vessel.

urbulent



23/40

Optical methods

Endoscopy

Endoscopy is a way oflooking inside the humanbody through a narrow,flexible scope. It ismostly used to diagnose

problems in theoesophagus, stomachand intestines, iulcers, bleeding atumours. If somethingsuspicious is seen, abiopsy(a small sampleof tissue) can be takenand examined later bpathologist to see whatit is. Typically opticalfibres are used to transfer light to the end of the endoscoand a miniature video camera records the image.Theyhave a biopsy channel (along which tissue can be taken orother surgical instruments can be passed) and water pipe f

washing the field of view clear.

ncludingnd

y a

pealso

or

Laparoscopy is an extension of this technique where thescope is used to look inside the abdomen and pelvis througha small cut, or incision.



24/40


In endscopic surgery, commonly known as keyhole surgery,the endoscope is passed through an incision into the patientand the surgeon, who uses knives or lasers also passed

though the scope, watches what he is doing on a videoscreen. Keyhole surgery can be used to treat hernias andremove tumours and is often used on sportstars' injuries asthe recovery time is faster than in normal open surgery.

Endoscopes for remote robotic surgeryare currently beingtested. In 2001, doctors in New York removed the gallbladder of a woman in France using an endoscope remotely.Endoscopic pills which include a camera and transmitter arecurrently being developed. This would allow the wholedigestive tract to be examined painlessly.


25/40

Pulse Oximetry

Oxygenated and deoxygenated bloodare slightly differentcolours and so absorb different frequencies of lightdifferently. By looking at the absorption of two differentfrequencies of light, we can distinguish between bloodcarrying oxygen and blood not carrying oxygen.

This principle is the

basis of one of themost commonly usedinstruments formonitoring the body -the pulse oximeter. Apulse oximeter clipsonto a finger (or ababy's foot) and has

inside it one red lightsource, one near-

infrared light source and a detector. As the blood pulses,more blood enters the finger and the amount of lightdetected decreases. However, the decrease in the amountof red light differs from the decrease in the amount of near-infrared light. The size of this difference depends on the

amount of oxygen in the blood. At the same time, the bloodmoves through the finger in pulses, allowing the heart rateto be measured.

The pulse oximeter is often used to monitor the well beingof patients in intensive care and anaesthetised patient.



26/40


Laser Surgery

Lasers produce light that has only one wavelength, ratherthan a range of wavelengths like most other light sources.They are very useful in surgery as they can be focussed to asmall point, enabling them to vaporise, seal or cut tissue.

Eye surgeryLaser eye surgery can be used to correct long or short sight,

and astigmatism (distorted vision). A surgeon cuts a thinlayer of the cornea off to create a flap. A laser is then usedto cut and reshape the cornea behind the flap. The flap isthen closed and grows back naturally.

Hair removalWhen laser light is shone onto the surface of the skin it isabsorbed by melanin, the pigment that gives hair and skintheir colour, and is converted into heat. If enough energy isabsorbed, the part of the hair follicle that causes hairgrowth is destroyed, and the hair cannot grow back.As the skin contains melanin as well, it also heats up andcan be damaged.

Two things allow laser hair removal to be done safely:

1) the hair follicle contains more melanin than the skin2) the surface area of skin is larger so it cools down

faster than the hair follicle

Laser hair removal therefore works best on people with paleskin and dark hair. A tan is caused by extra melanin beingproduced, so you should wait for a tan to fade before havinglaser treatment.


27/40

Mole RemovalMole removal works in a similar way to hair removal.Thepigment in the mole absorbs the energy from the laser

light and is broken up. It is then carried away by the bodyand when the skin heals its colour is the same as thesurrounding skin.

Port Wine StainsBlood vessels canwiden (dilate) to

allow more bloodthrough, so whenyou exercise andyour body needs toget rid of heat, theblood vessels in yourskin dilate and youlook red.


A port wine stain is an areaof red or purple skin. Theyare caused by blood vessels always being dilated, so theskin always looks red as it permanently contains a lot ofblood. About 3 in 1000 babies are born with a port winestain.

www.lumenis.com

Lasers can be used to destroy the tiny, dilated bloodvessels, without harming the surrounding skin. Treatmentworks better on children than on adults.


28/40

Magnetic Resonance Imaging (MRI)

MRI is a way of looking inside the body and is especiallygood at producing images of soft tissues such as muscle,fat, cartilage and the brain. It does this by producing a mapwhich depends on the density ofhydrogen in the body.

MRI uses a very strong superconducting magnet with amagnetic field strength of around 40 000 times that of theEarth. The nucleus of a hydrogen atom is a single proton,

and is like a little bar magnet.

When a personis lying in themagnetic fieldof the MRIscanner thenuclei of thehydrogenatoms in theirbody line up,like compassneedles in theEarth'smagnetic f

either pointinin thedirection ofthe field oropposite to it.

Magnetic Field

ield,

g



29/40

The hydrogen nuclei (protons) dont stay stillthough, but move like a spinning top around

the direction of the magnetic field.

A radiofrequency field, an alternating magnetic field thathas the same frequency as radio waves, is then applied. Thisflips some of the protons round and makes them all moveround together. This produces a changing magnetic field at

right angles to the large magnetic field, which can induce avoltage in a coil of wire. This signal can be used to producean image which, which depends on the number of protonsand how tightly they are held by surrounding molecules.

A third magnetic field has a gradient so it is stronger at oneend than the other. This allows the scanner to select a sliceof the body to look at, by selecting the required field

strength. The gradient fields change rapidly and make thescanner very noisy.

MRI is used for diagnosing manyproblems. It can be used toidentify tumours, diagnosemultiple sclerosis (MS) and isoften used on sportspeople tosee problems with ligamentsinside joints like the knee andankle. It can also be used toshow the anatomy of the brainand how it works.

MRI scan of a knee, courtesyof GE healthcare Ltd.



30/40

MRI doesn't use radiation, andmagnetic fields are thought to be

safe. However, MRI scanners arevery big and expensive. Also,because of the strong magneticfields, all metal objects have tobe kept out of the room or theywould get pulled into the scanner.People with pacemakers or other

implanted devices can't have MRIscans as the magnetic field wouldstop them working. An MRI scancan take up to 20 minutes to

complete and you have to be still the whole time as anymovement would blur the image. The changing magneticfields also produce a lot of noise, which can be scary, and asyou are inside the scanner during the scan, people with

claustrophobia can find the process upsetting.

MRI produces images that are2-D slices through the body andthey have excellent spatialresolution (i.e. you can see very

small details in the images),making it an important tool fordoctors.



31/40

ECG (Electrocardiogram)

If a patient complains of chest pains or shortness of breathit is important to check that their heart is working properly.The heart is a muscle made up of four chambers whichcontract to push blood and around the body. The messagesthat tell the muscle to contract are electrical signals, andby measuring these signals we can see if there is anythingwrong with the heart. This is done using an ECG.

To take an ECG, three electrodes are placed on the surfaceof the skin: one on the right arm, one on the left arm, andone on the left leg. These contacts are connected to amachine called an electrocardiograph. This draws lines ongraph paper showing the electric potential between eachelectrode over time.

Each voltagespike is due to anelectrical signalin the heart andis represented bya letter. A healthy heart should give a trace that lookssomething like this.

Changes to this pattern could indicate a problem such asmissed beats, no P-wave (the atria not contracting) or veryhigh spikes (the ventricles working too hard due to highblood pressure).



32/40

Bioengineering

Pacemakers

The muscles of the heart contract in a regular rhythm andwith a steady pace of about 70 beats per minute forsomeone at rest, and higher for someone who is exercising.The electrical signals that tell the heart muscles to contractcan stop working properly, causing the heart to beat to

irregularly or not at all. A pacemaker is an electronic devicethat makes the heart muscles contract at a regular rate.

There are two parts to a pacemaker; the generator and theleads.

The generator is about the size of a matchbox, and containsthe battery and a mini computer that processes informationabout the electrical signals in the heart and sends out itsown signals to tell the heart to beat. It is implanted justunder the skin by the left shoulder. The batteries last for upto ten years, and are checked regularly.

The leads are passed into the heart though a vein coming

from the left shoulder, and are implanted in the muscle ofthe wall of the right atrium and ventricle. When thewww.teachingmedicalphysics.org.uk 32


33/40

generator sends out an electrical signal, the leads pass it onto the heart and the muscle contracts, causing blood to bepushed through and out of the heart.

Medical Engineering

Medical Engineering is the design and manufacture of all

health related products. These include tools (includingrobotics) for surgery, scanners and hospital equipment,prosthetics or products that help people with health anddisability problems live more normal, comfortable lives.

A baby carrier for a parent in a wheelchair



34/40

Some new products include a mugthat only releases one sip at a time so

people with motor neurone diseasecan drink more easily, portable raisedtoiletseats to allow people withdisabilities to use public toilets, bikesfor children with growth problems sothey can play like other children and a'Smart House' to allow people with

dementia to live safely in their ownhome with as few noticeable changesas possible.

The Smart House gives verbal warnings if taps are leftrunning, it will reduce water flow in the taps if the bath

gets too full andautomatically turn off thecooker if a pan boils dry ogets too hot. There arealso verbal warnings bythe doors saying thingssuch as 'don't forget your

keys' and sensors underthe bed to automaticallyturn on the light if theperson gets out of bedduring the night.

r



35/40

Cochlear Implants

Cochlear implants are devices used to stimulate hearing in

people with severe to profound hearing loss.

They work using amicrophone, processorand transmitter outsidethe ear (left), and areciever and electrodesinside the head (right).

Sound waves cause the eardrum to vibrate, which sets thebones in the inner ear inmotion, which in turncauses the fluid in theinner ear to move.The cochlea in a healthy

ear contains hair cells.The motion of the fluidcauses the hair cells tovibrate. Nerve cells

detect this vibration and send a signal to the brain. Highpitched sounds which have high frequencies can only travela short distance along the membrane; low pitched soundscan travel further. In this way the brain can tell thedifference between high notes and low notes. Louder soundsdon't affect the distance along the membrane they cantravel, though they make the hairs vibrate more.

Damage to these hair cells, due to genetic muations, illness,chemical reactions or excessively loud noises, can lead tohearing loss.



36/40

When hearing using a cochlear implant:1) A microphone turns thesound into an electrical signal


2) A processor sorts the signalinto groups of frequencies.3) A transmitter sends thisinformation to the receiverinside the head usingradiowaves and the receiversends the required electrical

currents to the correct electrodes.4)Electrodes, which are implanted inside the cochlea,stimulate the nerve cells.5) The auditory nerve sends a message to the brain.

These devices, though they have been show to work well,are controversial.People who use signlanguage to communicate often see

themselves as part of a community.Some people object to implants as theyfeel they are destroying this cCochlear imp

ommunity.lants work best when

ren

Supporters of cochlear implants believe that people are

hat do you think?

Ltd.

implanted into young children. However, at this age childare too young to make the decision for themselves, andtheir parents must make the choice for them.

meant to be able to hear and an implant is therefore nodifferent to giving a child glasses to help them see.

W

Images courtesy ofCochlear Europe


37/40


The Future

Medical physics continues to play a valuable role inhealthcare. More and more hospitals are buying MRI and PETscanners and more people with disabilities are receivingincreasingly sophisticated devices.

Medical physicists are at the forefront of developments inhealthcare. In the NHS, medical physicists plan radiotherapytreatments and ensure that the equipment is safe. Theydevelop new methods using MRI and ultrasound, and assistpeople with disabilities. Medical physicists also work in bothuniversities and industry, where they lead research intoimproving existing techniques and developing completelynew ones.

For more details about jobs in medical physics, seewww.ipem.ac.uk,www.nhscareers.nhs.uk/nhs-knowledge_base/data/4847.html andwww.connexions-direct.com/jobs4u/jobfamily/healthcare/medicalphysicist.cfm?fd=1252.

For more on medical physics in general, seewww.teachingmedicalphysics.org.ukwww.ipem.ac.ukwww.cochlear.com/europewww.gehealthcare.com

And for some medical physics games, trywww.insidestory.iop.org


38/40


Glossary

Biopsy obtaining and examining a sample ofcells or tissue from the body.

Cyclotron a machine used to accelerate chargedparticles. For PET, protons areaccelerated, then smashed into atomswhich then become radioactive,emitting positrons.

Cyst pocket of tissue filled with fluid.

Diagnosis finding out what is wrong with a patient.

Endoscopy examining the body using a narrow tube.

Half-life the time taken for the activity of aradioisotope to drop by half.

Hearing loss people with profound hearing lossmostly rely on lip reading or signlanguage. People with severe hearingloss get help from powerful hearing aids,though may also rely on lip reading.

Ionising radiation An alpha or beta particle, or a highenergy electromagnetic wave, which hasenough energy to completely remove anelectron from an atom.

Mutation a change to genetic material (DNA).


39/40


Near infrared electromagnetic waves that are in theinfrared region of the spectrum, buthave frequencies near those of visible

red light (around 800 nm).

Oesophagus part of the digestive system (foodpipe/gullet).

Palliative a treatment intended to ease pain andsuffering rather than cure the patient.

Prosthetic something which artificially replaces apart of the body.

Radioisotope an isotope that is unstable and willdecay, emitting radiation.

Superconducting A magnet made by a current flowing in

magnet a coil of superconducting wire, which isso cold it no longer has any resistance.

Therapy treating the patient.


40/40

Acronyms

CAT - Computed Axial TomographyCT - Computed TomographyECG - ElectrocardiogramMRI - Magnetic Resonance ImagingmSv - millisievert, a unit of radiation exposurePET - Positron Emission TomographyRF- Radiofrequency2-D - Two dimensional3-D - Three dimensional4-D - Four dimensional (3 spatial dimensions and time)

Acknowledgements

This booklet was written by Emily Cook and Adam Gibson.

Many thanks to all those who contributed:Nicola Hannam.Jeff Jones.Dr David Sang.Prof. Angela Newing.Lucy Gibson.Dr Michael Hillman, Bath Institute of Medical

Engineering.Dr S E Jones, Gloucestershire Royal Hospital.The Charlotte Observer Collection, Public Library ofCharlotte & Mecklenburg County.Cochlear Europe Ltd.TMGE Healthcare Ltd.Lumenis Ltd.

Textbook a5

Documents

Transcript of Textbook a5