Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BDS3 CLINICAL Radiology > Physics Basics > Flashcards

Physics Basics Flashcards

1
Q

What are radiographs

A

• They are images created by X-rays which have been projected through an object (usually patient’s teeth and bone) and then interacted with a receptor on the other side

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are there different shades in radiographs

A

• The different shades of grey on the image correspond to the different types of tissue and thickness of tissue involved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why are radiographs useful

A

They provide the ability to see structures within the body, particularly mineralised tissue
• It can show normal anatomy and pathology
• It aids diagnosis, treatment planning and monitoring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is electromagnetic radiation

A

• Electromagnetic radiation is the flow of energy created by simultaneously varying electrical and magnetic fields and it is schematically represented as a sine wave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the properties of electromagnetic radiation

A

○ No mass
○ No charge
○ Always travel at speed of light (671 million mph)
○ Can travel in a vacuum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is frequency

A

how many times the wave’s shape repeats per unit time
○ Measured in hertz, Hz
○ (1Hz = 1 cycle per second)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is wavelength

A

distance over which the wave’s shape repeats

○ Measured in metres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is speed

A

frequency x wavelength
○ BUT speed of all EM radiation is a constant of 3x108 ms-1
Therefore if frequency increases then wavelength must decrease and vice versa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is photon energy

A
  • EM radiation involves the movement of energy as ‘packets of energy’ known as photons
    • Energy is usually measured in electron volts, eV
    • 1 eV = energy (in joules) gained by 1 electron moving across a potential difference of 1 volt
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are X-ray photon energies

A

• X-ray photon energies - 124eV - 124keV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the types of X-rays

A

○ Hard X-rays (higher energies)
§ Able to penetrate human tissues
○ Soft X-rays (lower energies)
§ Easily absorbed but we don’t want this for radiographs because we want the x ray to pass through the body and reach the receptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the property of x rays

A

• Form of EM radiation
○ No mass, no charge, very fast, can travel in a vacuum etc
• Undetectable to human senses (unlike visible light)
• Man mad (unlike gamma rays which are produced by radioactive decay)
• Cause ionisation i.e displacement of electrons from atoms and molecules
○ This process is what causes the dangerous side effects of X-rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the basic production of X-rays

A
  • Electrons are fired at atoms at very high speed
    • On collision, the kinetic energy of these fast moving electrons is converted to electromagnetic radiation (ideally X-rays) & heat
    • The X-ray photons are aimed at a subject
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What do atoms consist of

A

central nucleus

orbiting shells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does the central nucleus consist of

A

§ Protons (positive charge)

§ Neutrons (neutral)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does the orbiting shells consist of

A

§ Electrons (negative charge)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the charge of the nucleus

A

○ Protons and neutrons have a similar mass

○ There is an overall positive charge as neutrons are neutral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the atomic number

A

(Z) = number of protons and is unique to each element

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the mass number

A

(A) = number of protons + neutrons and this can change for the same element

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the number of electrons

A

• An atom in its ‘ground state’ is neutral
○ Number of electrons = number of protons
• Ionisation = removing/adding electrons to an atom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens if you remove/add an electron

A

○ If you remove an electron becomes a positive ion (because number of positive now outweigh negative)
○ If you add an electron it becomes a negative ion

22
Q

What are the electron shells

A

• Electrons spin around the nucleus in discrete orbits/shells
○ Cannot exist between these shells
• Each shell is labelled alphabetically
○ Innermost shell is K
○ Then L, M, N, O etc
• Electros try to fill available spaces in the inner shells first

23
Q

How is the max number of electrons in a shell calculated

A

• The maximum number is 2n2 where n is the shell number (K is 1, L is 2 etc)

24
Q

How are orbiting electrons held in

A

• Orbiting electrons are held within their shells by electrostatic force - this is due to the negative charge of electrons being attracted to the overall positive charge of the nucleus

25
Q

How do you remove an electron from its shell

A

a specific amount of energy is required to overcome this attraction
The binding energy is the additional energy required to exceed electrostatic force

26
Q

What is binding energy

A
  • The closer to the nucleus, the greater the electrostatic force and therefore binding energy
    • K shell electrons have the highest binding energies, then L, M, etc
    • The more positively charged the nucleus (i.e higher Z) the greater the electrostatic force
27
Q

What is the amount of energy required to move from one shell to another

A
  • The specific amount of energy required to move an electron to a more outer shell equals the difference in the binding energies of the 2 shells
    • Conversely if an electron drops to a more inner shell then this specific amount of energy is released possibly in the form of X-ray photons (if sufficient energy)
28
Q

What is the energy required to move an electron from K shell to L shell in a tungsten atom

A

○ Binding energy of K shell - binding energy of L shell

29
Q

What does the dental x ray unit consist of

A 
○ Tube head 
		○ Collimator
		○ Positioning arm
		○ Control panel 
		○ Circuitry
30
Q

What are the electricity fundamentals

A

○ Current
○ Voltage
○ Transformers

31
Q

What is current

A

• Flow of electric charge, usually by the movement of electrons

32
Q

What is the unit for current

A

• SI unit: amp (or ampere), A, is a measure of how much charge flows past a point per second

33
Q

What are the different directions of current

A

direct current

alternating current

34
Q

What is direct current

A

constant unidirectional flow e.g batteries

35
Q

What is alternating current

A

flow repeatedly reverses direction
§ Flow periodically reverses direction
§ The number of complete cycles (reverse + reverse-back per unit time is the frequency)

36
Q

What is the unit for alternating current

A

hertz, Hz (cycles per second)

37
Q

What is the mains electricity

A

mains electricity is 50Hz in the UK - this means the current reverses and reverses back in 50 times a second

38
Q

What is rectification of current

A
  • X-ray production requires a unidirectional current but X-ray units are powered by mains electricity (AC)
    • X-ray units have generators which modify the AC so that it mimics a constant DC in a process known as rectification
39
Q

What is voltage

A
  • Difference in electrical potential between 2 points (a negative and positively charged point) in an electrical field
    • Related to how forcefully a charge will be pushed through an electrical field (through these 2 points)
40
Q

What is the unit of voltage

A

SI unit: volt, V

41
Q

What is the electrical supply in the mains supply in the uk

A

○ Alternating current (<13 amps)

○ 220-240 volts

42
Q

What is the dental x ray unit

A

○ Required direct current which is solved by rectification
○ Requires 2 different voltages
§ One as high as 10s of thousands of volts
§ One as low as around 10 volts

43
Q

What are transformers

A

• Transformers alter the voltage (& current) from one circuit to another

44
Q

What are the transformers required for X-ray unit

A

step up transformer

step down transformer

45
Q

What is a step up transformer

A

One takes the main supply and changes it so its appropriate for the X-ray tube (cathode-anode)
§ Increases potential difference across the X-ray tube in the unit
§ Usually 60,000-70,000 volts (60-70kV)
§ Current reduced to milliamps (mA)

46
Q

What is a step down transformer

A

one takes the main supply and changes it so it is appropriate for the filament
§ Decreases the potential difference across the filament
§ 10 volts
§ 10 amps

47
Q

What is an X-ray beam

A
  • Made up of millions of X-ray photons directed in the same general direction
    • Photons effectively travel in straight lines but diverge from the X-ray source (do not travel in parallel)
48
Q

What is the x-ray beam intensity

A
  • The strength of the X-ray beam is known as intensity
    • It is measured as the quantity of photon energy passing through a cross-sectional area of the beam per unit time
    • The greater the number and/or energy of photons = greater intensity
    • It is proportional to current in the filament (mA) and the potential difference across the X-ray tube (kV)
49
Q

Why should we be far away from the beam

A

its divergent
• Dose decreases with distance from X-ray source
• Ensure staff stand a sufficient distance from patient and not in the direction of the primary X-ray beam

50
Q

What is the inverse square law

A
  • Intensity of X-ray beam is inversely proportional to the square of the distance between the X-ray source and the point of measurement
    • Intensity = 1/distance2
    • Therefore, doubling the distance will quarter the dose

BDS3 CLINICAL Radiology (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions