Lecture 6

Question 1

What is the difference between radiography and radiology?

Answer 1

• Radiography = the use of X-rays to create a formed image - Radiology = the interpretation of normal and abnormal findings

Question 2

What are the basic steps that are involved in the process of radiography? (7 steps)

Answer 2

1. X-ray production 2. Beam attenuation to the patient 3. Image formation (receptors, film screen and digital) 4. Image processing (analogue and digital) 5. Quality assessment and controls 6. Radiation safety 7. Image geometry and patient factors

Question 3

_________ is the energy that is needed to eject an electron from its shell. It ______ as we go further to the base level of electrons.

Answer 3

1. Binding energy 2. Increases

Question 4

What does an atom become when it looses electrons ___. How does the net charge becomes more ________.

Answer 4

1. ion 2. positive

Question 5

What is the formula for velocity of an electromagnetic wave?

Answer 5

Velocity = frequency times wavelength

Question 6

As wavelength decrease. Total energy _____

Answer 6

1. increases

Question 7

What are the units that are used to measure wavelength, energy and frequency?

Answer 7

1. wavelength unit = meters/nanometers/angstroms 2. Energy unit = eV (electron volts) 3. Frequency = hertz (Hz)

Question 8

What are the properties of X-rays?

Answer 8

1. Electromagnetic waves – refraction, reflection, propagation & scatter radiation 2. Discrete Energy Bundles – Photoelectric effect (PE), absorption, fluorescence 3. Travel in straight lines 4. Produce small amount of heat passing through the tissue 5. Cannot be focused by a lens – we can only focus the electrons not the beam itself 6. Not affected by electric or magnetic fields 7. Penetrating- high energy, form image meaning potential for safety issues 8. Produce fluorescence 9. Affect film and imaging plates to form an image 10. Ionising- elimination of electrons from energy cells are responsible for the biological effects 11. Biological effects means cell destruction, carcinogenesis and genetic effects

Question 9

Name A, Z and X

Answer 9

A = mass number

Z = atomic number

X = chemical element/symbol

Question 10

What are the components that are found on the control panel of an X-ray machine?

Answer 10

1. Kilovoltage (kV or KVp- meaning maximum kilovolts)
2. mA control (millamperage) sometime the seconds control is combined in with this
3. Time control (either by itself or combined with mA)
4. Line Voltage control (actual voltage in real time)
5. Exposure button
6. Pre-exposure button

Question 11

i) What are the components of a cathode tube?
ii) Is it postive or negative electrode?
iii) High voltage or a low voltage circuit?

Answer 11

i) Coiled filament wire, a focusing cup and small and large focal wires
ii) negative electrode
iii) Low voltage circuit

Question 12

i) What are the components of an anode?
ii) Is it high/low voltage circuit?
iii) Is it a postive or a negative electrode?

Answer 12

i) Target and a focal spot
ii) High voltage circuit
iii) postive electrode

Question 13

What setting controls the size of the electron cloud?

Answer 13

mA setting controls the size of the electron cloud

Question 14

What is a problem with continually pressing the pre-exposure button?

Answer 14

Results in cathode damage

Question 15

What does the exposure button do?

Answer 15

Creates a potential difference across the tube

Question 16

What is the result on the kinetic energy of increasing the kV controls?

Answer 16

Increases kinetic energy on collision

Question 17

What is the charge of the focusing cup around the cathode and what is it’s function?

Answer 17

The charge of the focusing cup is negative and the function of it is to focus the electron stream

Question 18

What percentage of energy of anode collisons result in radiation being produced?

Answer 18

Only about 1% of collision will result in radiation being produced

Question 19

What are the two different types of radiation that make up the primary X-ray beam, what is the relative percentage of them and what causes them?

Answer 19

1. Bremsstralung radiation (BR) -75 to 90% - collisons with nucleus
2. Characteristic radiation (CR)- 10 to 25%- inner shell electrons

Question 20

What two factors influence the energy of the Bremsstrahlung radiation and when does the maximum ray beam occur?

Answer 20

Energy of BR formed: initial energy of incomming e- and angle of deviation at nucleus. The maximum energy loss occurs with a nucleus collision.

Question 21

What is the effect of changing mAs on the beam?

Answer 21

1. Increases the mAs (increasing size of e- beam and time crossing tube)
2. Increases collisions at target
3. Increase number of BR formed
4. Increasing intensity of the beam (number of BR per area)

Question 22

What is the effect of changing the mAs of the beam on the radiograph?

Answer 22

Increases the radiographic density only it has no effect on the energy. It will only increase the film blakcness if the energy of the bremstrunng radiation is high enough energy.

Question 23

What is the effect of increasing the kV value of the primary beam?

Answer 23

• High kV means higher kinetic energy of electron at target
• Increased BR Max E
• Increased BR Average E
• Increased number of BR

Question 24

What is the effect of increasing the kV on the radiograph?

Answer 24

Increased energy of the beam: means increased penetration, decreased contrast and increased radiographic density

Increased intensity of the beam: increased radiographic density of the beam

Question 25

What is the caused of the peaks on a primary beam BR spectrum and what causes them?

Answer 25

Caused by characteristic radiation and they are equal to the difference in binding energy between shells of electrons

Question 26

What is meant by the heel effect and how can it be used to your advantage?

Answer 26

The result of uneven beam density means that the beam has a higher intensity on the cathode side. It can be utilised with thicker body parts

Question 27

What factors influence the maximum exposure times for X-rays?

Answer 27

1. The focal spot size 2. The heat capacity of the target 3. Circuits and power supply

Question 28

What is the difference between effective focal spot and the actual focal spot size?

Answer 28

- The actual focal spot is the size of the focal spot whereas the effective focal spot is actual sized viewed from the window

Question 29

Describe one benefit of a large focal spot and one benefit of a smaller focal spot:

Answer 29

- Large focal spot allows for greater heat dissipation and greater overall exposures - Smaller focal spots allow increased detail and edge sharpeness

Question 30

What is the benefit of a rotating anode?

Answer 30

Rotates during exposures allowing heat to be spread over a much wider area.

Question 31

What is the problem with the use of combined circuits?

Answer 31

1. Combined circuits means lower mA values 2. kV and mA are no longer independant 3. Only way to increase it is to increase the time