Topic 2 - X-rays and ECGs

Question 1

What is thermionic emission

Answer 1

releasing electrons from a surface

Question 2

how do you produce x-rays

Answer 2

a filament acts as a cathode and is heated which gives more energy to its electrons, Once they have enough energy, they escape, this is called thermionic emission. The electrons are then accelerated towards the anode by a potential difference between the cathode and the anode. Electron beams can be used to produce x-rays when the electrons collide with a metal target (the anode) some of their kinetic energy is converted into x-rays. This is done in a glass tube that contains a vacuum

Question 3

Why is producing x-rays done in a vacuum with lead casting.

Answer 3

Vacuum- to stop electrons colliding with air particles that would knock them off target and decrease their energy Lead casing - to absorb some of the x-rays so they’re only aimed at the thing in question

Question 4

How can x-rays harm the body

Answer 4

They have a very high frequency and so high energy. They have enough energy to be able to ionise molecules in living cells.

Question 5

What happens when something is ionised

Answer 5

removing electrons from atoms, leaving them as positively charged ions. Ionisation means that cells might be damaged or destroyed which can lead to tissue damage or cancer.

Question 6

What does the intensity of radiation depend on?

Answer 6

The distance from the source because the same amount of radiation is hitting a smaller area.

Question 7

What is inverse square relationship?

Answer 7

If you move twice as far from the source the same radiation is being spread over 4 times the area so you only receive 1/2² of the intensity.

Question 8

How does the type of material affect the amount of x-ray absorption

Answer 8

The more dense/thicker a material the more radiation it absorbs.

Question 9

Which materials are mainly used to reduce peoples exposure to x-rays

Answer 9

lead and concrete

Question 10

What are fluoroscopes

Answer 10

Moving images of the inside of a patients body

Question 11

How do fluoroscopes work?

Answer 11

Place a patient between an x-ray source and a fluorescent screen. Different amounts of x-rays are absorbed as they pass through the patients body. Intensity depends on what they’ve been passed through. X-rays hit a fluorescent screen which absorbs the x-rays and fluoresces (give off light) to show a live image on the screen. The higher the intensity of x-rays the brighter the screen.

Question 12

How is modern fluoroscopy better?

Answer 12

An image intensifier is used to increase the brightness of the image so a lower dose of x-rays can be given to a patient. the screen is attached to a computer so the images can be recorded.

Question 13

What is fluoroscopy used for?

Answer 13

Used to diagnose problems in the way organs are functioning.

Question 14

What is a contrast medium

Answer 14

because x-rays pass through soft tissues easily the patient is given a contrast medium (by injection or ingestion). This is a substance which improves the contrast of the image seen by enhancing the soft tissue, making it more visible

Question 15

What are CAT scans

Answer 15

Computerised axial tomography. 2d image of slice through the body

Question 16

How do CAT scans work

Answer 16

An x-ray beam rotates around the body and is picked up by thousands of detectors. A computer works out how many of the x-rays are absorbed and produces a high quality image which is useful for diagnosing less obvious problems

Question 17

How can CAT scans be used to make 3d image

Answer 17

Stack the individual slices

Question 18

What are CAT scans used to check for

Answer 18

tumours and cancer

Question 19

What are the benefits of x-rays

Answer 19

Better to diagnose someone properly rather than give wrong treatment.

Hospitals limit x-ray exposure and reduce risk to patient as much as possible

Non invasive procedure/quick

Question 20

What part of the body can generate potential difference

Answer 20

muscle cells. There is a potential difference between the inside of a muscle cell and the outside. When its at rest its called resting potential

Question 21

How is resting potential measured

Answer 21

with small needle electrodes

Question 22

What is the normal resting potential

Answer 22

-70 mV (millivolts)

Question 23

What happens to the potential difference when a muscle cell is stimulated

Answer 23

It changes to +40 mV. The increased potential is called action potential, it passes down the length of the cell making the muscle cell contract

Question 24

What is an electrocardiograph

Answer 24

records the action potentials of the heart using electrodes stuck onto the chest, arms, and legs. For accurate readings patient should lie still and relax

Question 25

What happens to the heart when it beats in terms of potential difference

Answer 25

An action potential passes through the atria making them contract. A fraction of a second later another action potential passes through the ventricles making them contract. Once the action potential has passed the muscle relaxes

Question 26

What is an ECG

Answer 26

a graph of the results from electrocardiograph. Electrocardiogram

Question 27

Describe it

Answer 27

The horizontal line is the resting potential The ‘blip’ at P shows contraction of atria The QRS blip shows the contraction of ventricles, weird shape because of relaxation of atria as well. T is relaxation of ventricles

Question 28

How do you convert from Hz to bpm

Answer 28

Hz x 60

Question 29

What is a pacemaker?

Answer 29

Device used to regulate heart rate

Question 30

Why do some people need pacemakers?

Answer 30

heart rate isnt fast enough

Pulses irregularly

Problems with electrical signals being sent

Question 31

How do artificial pacemakers work

Answer 31

produces small electric impulses to stimulate the heart to beat. Impulses sent via electrodes (thin wires attatched to the heart)

Question 32

What are the problems with pacemakers?

Answer 32

Involves surgery (but only minor)

Powered by batteries so will need replacing when it loses power

Question 33

What are the advantages of modern pacemakers?

Answer 33

Can be programmed externally so settings can be changed without surgery

Some can monitor things such as breathing and temperature and then adjust heart rate accordingly.

Question 34

What is a pulse oximeter

Answer 34

Check % oxygen in blood

Question 35

How do pulse oximeters work?

Answer 35

Haemoglobin changes colour depending on the amount of oxygen in the blood. When theres lots of oxygen its bright red (oxyhaemoglobin), when it has given up its oxygen to cells its purple (reduced haemoglobin).

Pulse oximeter has a transmitter which emits two beams of red light and a photo detector to measure light. It is placed on thing part of body (finger/ear lobe). Beams of light pass through tissue and some light is absorbed by blood reducing the amount of light detected. The amount of light absorbed depends on the colour of the blood so the oxyhaemoglobin content.

Question 36

What % oxyhaemoglobin do healthy people have in arteries?

Answer 36

at least 95%

Question 37

What is reflection pulse oximetry?

Answer 37

reflects light off red blood cells instead of shining light through part of the body