2: Medical uses of endoscopes

medical

physics

A risk in using an endoscope is that the part of the endoscope inside the body

can tear tissues while it is being moved about. Endoscopic examination of the

bowel presents a particular risk, because the bowel contains bacteria, which, if they

enter the bloodstream, can produce a fatal infection. However, the risk in using

an endoscope is much less than the risk encountered if the abdomen had to

be opened up in conventional surgery. The fact that a patient usually has to be

sedated or anaesthetised presents another minor risk to the patient, although this

type of risk is the lesser problem when weighed against the alternative of an

undiagnosed or untreated problem.

Endoscopes that have been modified with surgical instruments can be used

to remove tissue samples for testing. This process is called a biopsy, and this is

one of the most common endoscopic procedures.

A common example of a biopsy is the removal of polyps or other growths from

the intestine for further examination and testing. Endoscopy reduces this risk because

the incisions and amount of cutting is minimised. Figure 18.2.1 shows a biopsy

being performed within the abdomen. The sample of tissue cut off can then be placed

or sucked into a tube attached to the endoscope and withdrawn from the body.

Minimally invasive surgery is conducted using optical fibre instruments that

are often an integral part of the endoscope. Surgery that is commonly carried out

with the aid of an endoscope includes removal of the gall bladder and the prostate,

and repairs to damaged tissues in joints. A common joint operation is the repair

of the anterior cruciate ligament in the knee (Figure 18.2.2). This part of the

anatomy is frequently torn in sports such as netball and football, which involve

vigorous twisting forces on the knees. People once condemned to months off the

sporting field by knee injuries are now returning to their sport within weeks,

because of endoscope-aided surgery.



Explain how an endoscope is

used in:

• observing internal organs

• obtaining tissue samples of

internal organs for further

testing.



Figure 18.2.1



A biopsy from within

the abdomen



Figure 18.2.2



External view of surgery to

repair an anterior cruciate

ligament



Developments in endoscopy



A



n endoscopic capsule (Figure

18.2.3) is an endoscope with

no optical fibres! This small

capsule can be swallowed by the

patient and contains a wireless

camera that can pass through the

intestinal system and report via

video link what is observed.

This will improve endoscopic

observation of the digestive tract.



optical dome

lens holder

illuminating LEDs

lens

battery



antenna



Figure 18.2.3



An endoscopic capsule



Checkpoint 18.2

1

2



List the advantages and disadvantages of endoscopy.

Outline how a biopsy is done.

337



18



Imaging

with light



PRACTICAL EXPERIENCES

CHAPTER 18



This is a starting point to get you thinking about the mandatory practical

experiences outlined in the syllabus. For detailed instructions and advice, use

in2 Physics @ HSC Activity Manual.



Perform a first-hand

investigation to demonstrate

the transfer of light by optical

fibres.

Gather secondary information

to observe internal organs

from images produced

by an endoscope.



Activity 18.1: Optical fibres

Many light shops sell products known generally as ‘optical fibre lights’, which

consists of numerous fibre optic tubes through which coloured light is passed via

some colour-changing mechanism. Obtain one of these tubes and use a LED or

laser light to shine light through the tube. Change the direction of the illumination

by moving the end of the tube in different directions.

Equipment: optical fibre (e.g. from an optical fibre lamp), light source (LED),

power supply.

Discussion questions

1 Identify what optical fibres are made of and explain how something

so brittle can be made so flexible.

2 Explain how light is transferred down an optical fibre.

3 Explain how optical fibres are used in an endoscope to transfer images

from inside the body.



Figure 18.3.1



338



An optical fibre lamp



Chapter summary

•

•

•

•

•



An endoscope is an optical instrument that allows

real-time observation of internal organs.

Light is transmitted through optical fibres by total

internal reflection.

Cheaper non-coherent bundles of fibres carry the light

into the body.

More expensive coherent bundles carry the image out

of the body.

Advantages of endoscopy

– The tissues and organs are seen in real colour.

– Imaging is in real time, enabling the doctor to

respond to what is seen.



•



medical

physics



– It allows minimally invasive tissue sampling and

minor surgery that is safer and cheaper, with quicker

recovery than open surgery.

– The process uses non-ionising radiation, namely

light, an advantage over X-rays.

Disadvantages of endoscopy

– It is more time consuming than ultrasound and

X-rays.

– It presents minor risks to the patient, especially if

an anaesthetic is required. Operations on the bowel

involve a risk of infection.

– Only the surface of tissues is visible.



Review questions

Physically Speaking



5 Explain how an endoscope is used to obtain tissue



Use some of the chapter key words to complete

the following paragraph.



6 Recall an investigation that you carried out to



The medical technique known as ________________ allows

minimally invasive procedures such as ________________

to be performed via a body opening or a small incision.



samples from the stomach of a patient.

demonstrate the transfer of light by optical fibres.



7 Assess the advances in medical techniques as the

result of the use of endoscopes.



8 Explain why endoscopic surgery is often referred to

as ‘keyhole surgery’.



The ________________ allows a surgeon to view internal tissues

through the ________________ while it is illuminated via the

________________. An ________________ works because light is



Solving problems



confined to the ________________ enclosed by the



9 Determine the angle of refraction of light that passes



________________ of a fibre by ________________.



Reviewing

1 Explain the importance of total internal reflection to

the operation of an endoscope.



2 Compare the structure of coherent and non-coherent

fibre bundles.



3 Compare the function of coherent and non-coherent



from water (n = 1.33) to glass (n = 1.48) at an

incident angle of 30º.



10 Determine the critical angle for a material with

refractive index of 1.4 that is immersed in:

a glass (n = 1.48)

b water (n = 1.33)



11 A critical angle of 48.75° is measured at the

boundary between air (n = 1) and another medium.

Calculate the refractive index of the medium.

Can you identify the probable medium?



fibre bundles in an endoscope.



4 Explain how an endoscope is used to observe



Re



iew



Q uesti o



n



s



v



internal organs.



339



19

radioactive decay, radiation,

radioactive, radioisotopes, nucleons,

atomic number, mass number, isotopes,

alpha decay, alpha particle, beta decay,

beta particle, positron decay, antiparticle,

positron emission tomography (PET),

gamma decay, half-life,

radiopharmaceuticals, nuclear reactor,

cyclotron, gamma camera, bone scan,

collimator, scintillator, single-photon

emission computed tomography (SPECT)



Imaging with

gamma rays

Radioactivity can be good!

Images made using ultrasound, X-rays and visible light can show

anatomical structures rather well. They all involve sending various

forms of energy into the body. A rather different approach is to

introduce radioactive elements into a person’s body and study the

radiation that emerges. Images can be made of the bones as well

as soft tissues including the brain, heart, liver and thyroid. Rather

remarkably, this approach allows the production of images from

outside the body that show how a person’s organs are functioning.

Here we consider two of these minimally invasive but powerful

diagnostic tools: bone scans using radioactive tracers

and positron emission tomography.



19.1 Isotopes and radioactive decay

Outline properties of

radioactive isotopes and their

half-lives that are used to

obtain scans of organs.



340



For the 30 or so lightest elements, the number of protons is roughly the same

as the number of neutrons in the nucleus in most of their naturally occurring

isotopes. These isotopes are stable. However, many elements have isotopes whose

nuclei have too few or too many neutrons. These isotopes are unstable and

undergo radioactive decay in which they change and emit radiation. The type

of radiation that is emitted depends on the nature of the decay (see in2 Physics

@ Preliminary section 15.5).

There are 82 elements that have at least one stable isotope. The stability

depends on the ratio of protons to neutrons. As the atomic number increases,

the ratio of neutrons to protons needed for stability also increases.

Many elements have naturally occurring unstable isotopes. These are

called radioactive isotopes or radioisotopes. The nucleus of a radioisotope

(the parent nucleus) usually transforms itself into another nucleus (the daughter

nucleus) by emitting particles and energy. It will decay repeatedly until it forms

a daughter nucleus that is stable.



medical

physics



increasing

distance



Isotopes



A



maximum

shielding



reducing time of exposure



Figure 19.1.1



Reducing the danger from radiation involves increasing distance,

maximising shielding and reducing the time of exposure.



Alpha decay

Some unstable nuclei decay by emitting a particle that

contains two protons and two neutrons in a process known as

alpha decay. The remaining nucleus has a mass number that is

reduced by 4 and an atomic number that is reduced by 2. This

particle emitted from the nucleus is called an alpha particle

(α-particle). Alpha particles are helium nuclei ( 42 He ) and they

rapidly become helium atoms, as they gain electrons from the

surroundings. Such reactions are the source of most of the

helium on Earth.

For example, radioactive uranium-238 undergoes alpha decay

to produce thorium-234. The daughter nucleus has 2 protons

less than the parent nucleus and so it is a different element. In

a nuclear reaction, both mass number and charge are conserved,

and the decay process can be described by an equation:

238

92 U



→



234

90Th



n atomic nucleus consists of nucleons—

 

protons and neutrons. The number of

protons in the nucleus is called the atomic number,

while the total number of nucleons is called the

mass number. Atoms of the same element with

different numbers of neutrons are called isotopes of

that element. Many isotopes occur naturally, but

some are made artificially.

  In section 15.4 of in2 Physics @ Preliminary

we represented this information in a compact form.

For example, an important isotope of fluorine is:

Mass number

18

Atomic number

9



It is called fluorine-18, with 18 being the mass

number. Other isotopes that are important in

medicine include carbon-14, iodine-131,

phosphorus-31 and technetium-99. Hydrogen is the

only element that has special names for its three

isotopes: hydrogen, deuterium and tritium.



electron

proton



Beta decay

When a radioactive nucleus undergoes beta decay, a

neutron changes into a proton, releasing a high-energy electron

in the process. The electron is ejected from the nucleus with such

a high velocity that it totally escapes the atom. An electron

(represented as e– or −10e) emitted from the nucleus in this way is

called a beta particle (β-particle). An electron has only 1/1836



1

1H hydrogen



neutron

2 neutrons



+ 42 He



or illustrated by a diagram (see Figure 19.1.3).

An alpha particle can only travel a few centimetres in air

before it loses its kinetic energy and gains electrons to become a

helium atom. In living tissue the range is about 50 µm, about

half the width of a human hair. Due to their relatively large mass,

alpha particles carry a lot of energy and have a high ability to

ionise the surrounding medium, making them very dangerous

to living cells. They are not used very much in medicine.



F



proton

electron



Figure 19.1.2



proton

3

1H tritium



electron

2

1H deuterium



Isotopes of hydrogen—each with one proton

and one accompanying electron



daughter nucleus

Th-234

parent nucleus

U-238



Figure 19.1.3



4

2He



alpha particle

(helium nucleus)



Uranium-238 undergoes alpha decay



341