P3.2 X-rays and ECGs

Question 1

What does ionising radiation do?

Answer 1

Turn atoms into ions by removing some of their outer electrons

Question 2

What happens when the energy of an X-ray increases?

Answer 2

It becomes more ionising

Question 3

How do you increase the energy of an X-Ray?

Answer 3

You increase its frequency and voltage

Question 4

What is a negative electrode called?

Answer 4

A cathode

Question 5

What is a positive electrode called?

Answer 5

An anode

Question 6

What happens when you heat the cathode in an X-ray machine?

Answer 6

It becomes an electron gun

Question 7

What is the process of an electron gun emitting electrons called?

Answer 7

Thermionic emission

Question 8

What happens when there is a large potential difference between the anode and the cathode?

Answer 8

The electrons accelerate towards the anode

Question 9

Why does an X-ray machine have an evacuated tube?

Answer 9

So that the electrons don’t collide with other particles as they cross the tube

Question 10

What is an evacuated tube?

Answer 10

A tube from which the air has been removed so that there is a vacuum

Question 11

What happens to the kinetic energy of electrons when they hit the anode?

Answer 11

Most of it is transferred to thermal energy, but some are transformed into X-rays

Question 12

How do you increase the amount of X-rays?

Answer 12

You make the coil hotter (cathode) so that more electrons are emitted from the electron gun

Question 13

What is another name for an X-ray machine?

Answer 13

X-ray tube

Question 14

Why does the anode in an X-ray machine spin?

Answer 14

• to reduce wear

- to prevent it from overheating

Question 15

At what angle are X-rays emitted to the electron beam?

Answer 15

90 degrees

Question 16

What is current?

Answer 16

The rate of flow of electrons

Question 17

How do you find current?

Answer 17

I = N x q
Current = number of particles flowing each second x charge on each particle

Question 18

How do you find the kinetic energy of an electron?

Answer 18

E = 1/2mv^2 or E =eV

Question 19

What does m stand for in the formula used for finding kinetic energy?

Answer 19

Mass of an electron in kg

Question 20

What does v stand for in the formula used for finding kinetic energy?

Answer 20

Velocity of the electron in m/s

Question 21

What is kinetic energy measured in?

Answer 21

Joules or kgm^2/s^2

Question 22

What does V stand for in the formula for finding kinetic energy?

Answer 22

Potential difference in volts

Question 23

What does e stand for in the formula for finding kinetic energy?

Answer 23

Charge of an electron

Question 24

What is the charge of an electron?

Answer 24

1.6 x 10^-19 C

Question 25

When you double the distance away from a radioactive source, what happens to its strength?

Answer 25

It decreases to a quarter

Question 26

How do you find out how the strength of a radioactive source changes in relation to distance?

Answer 26

By using the inverse square law

Question 27

What does the inverse square law state?

Answer 27

The strength of a wave is inversely proportional to the square of the distance from the source

Question 28

When the density of a material increases, what happens to the amount of X-rays it absorbs?

Answer 28

It increases

Question 29

Why does bone show up lighter on an X-ray than organs or tissues?

Answer 29

- Bone is denser than organs or tissues so it absorbs more X-rays - on X-rays dark areas are where a lot of X-rays have been detected - because the bone has absorbed a lot of X-rays not many are detected by the scanner - this means it shows up as white because of negative imaging

Question 30

How does a computer build up a 3D image from a CAT scanner?

Answer 30

It builds up many cross-sectional views of the body gotten from the scanner

Question 31

What do unusual areas of brightness or darkness indicate on a CAT scan picture?

Answer 31

Tumours or small areas of tissue that have died because their blood supply has been obstructed

Question 32

What do fluoroscopes do?

Answer 32

Show a patient's organs working

Question 33

What can fluoroscopes be used for?

Answer 33

Detecting blocked blood vessels

Question 34

How does a fluoroscopy get a moving image of the inside of the body?

Answer 34

It uses an X-ray detector attached to a digital video camera. The patient is put between this and the source

Question 35

What are the benefits of CAT scans and fluoroscopes?

Answer 35

- painless for the patient - non-invasive - no biopsy

Question 36

How is the risk of damaging other tissues minimised when treating cancer with X-rays?

Answer 36

They're fired from several different directions so that only the tumour receives a high dose

Question 37

What is an action potential?

Answer 37

An electrical signal that is sent to each muscle cell to tell it when to contract

Question 38

Why does the human body conduct electricity?

Answer 38

It contains a high proportion of water with dissolved salt in it

Question 39

What does ECG stand for?

Answer 39

Electrocardiogram

Question 40

What is an ECG?

Answer 40

A picture of the heart's electrical signals

Question 41

What does an ECG show?

Answer 41

- how fast the heart is beating | - which part of the heart might not be working properly

Question 42

How much time is one large square on an ECG equal to?

Answer 42

0.2 seconds

Question 43

How do you find out the frequency of a heart beat in beats per second?

Answer 43

``` f = 1/t frequency = 1 / time period in seconds ```

Question 44

How do you find the time period of a heart beat?

Answer 44

You work out the average length of one heartbeat

Question 45

How does one action potential spread across the heart?

Answer 45

- the sino-ventricular node contracts - the action potential spreads across both atria - the atrio-ventricular node contracts - the action potential spreads up the ventricle walls - a contraction spreads up from the base of the ventricles

Question 46

What is the frequency of a heart beat usually given as?

Answer 46

bpm, beats per minute

Question 47

What is pulse oximetry used for?

Answer 47

- measuring the pulse rate of a person | - seeing how much oxygen their blood is carrying

Question 48

What does a pulse oximeter consist of?

Answer 48

- a LED emitting red light - a LED emitting infrared - a detector

Question 49

What does LED stand for?

Answer 49

Light emitting diode

Question 50

What does oxygenated blood absorb more of in comparison to deoxygenated blood in a pulse oximeter?

Answer 50

Infrared

Question 51

What does deoxygenated blood absorb more of in comparison to oxygenated blood in a pulse oximeter?

Answer 51

Red light

Question 52

How does a pulse oximeter work out a pulse?

Answer 52

Each beat of the heart causes a surge of oxygenated blood, so the oximeter looks at the peaks of infrared absorbance

Question 53

How does a pulse oximeter work out how much oxygen the blood is carrying?

Answer 53

By comparing the absorbance between the red light and infrared LEDs

Question 54

How is the amount of oxygen the blood is carrying expressed in an oximeter?

Answer 54

As a percentage of its maximum

Question 55

What does a pacemaker do?

Answer 55

Detect, amplify and transmit action potentials to other parts of the heart so that its chambers contract correctly

Question 56

What can be used when someone's heart doesn't beat properly?

Answer 56

A pacemaker

Question 57

Where do you put a pulse oximeter?

Answer 57

A finger or a toe