Radiography

Question 1

Where does x-ray production occur?

Answer 1

X-ray tube head

Question 2

How does the cathode differ between sophisticated and portable x-ray machines

Answer 2

Sophisticated machine - much higher current (mA) which causes more heating of the filament and releases more x-rays.
Portable machine - low mA so the filament is heated to a lower temperature and less electrons are released.

Question 3

Briefly explain Potential Difference

Answer 3

A high voltage is applied to the anode side so that there is a voltage differential between the cathode and anode

Question 4

The positive side of the tube head is the?

Answer 4

Anode

Question 5

The negative side of the tube head is the?

Answer 5

Cathode

Question 6

What does kV control?

Answer 6

Voltage

Question 7

What does increasing kV do to the electrons?

Answer 7

Increases voltage - increases speed of electrons - increases energy of the x-rays - increases the penetrating power of the beam

Question 8

Which type of rectification is preferable?

Answer 8

3 phase (electrons are hitting the anode continuously rather than in bursts) - reduced kV fluctuation

Question 9

What is rectification?

Answer 9

How often during the exposure time the voltage is applied to the anode and therefore how often electrodes are flowing.

Question 10

In what way is a rotating anode beneficial?

Answer 10

Gives a larger surface area for heat to dissipate

Question 11

Which effect allows us to see different shades of gray in x-rays and why?

Answer 11

The photoelectric effect - differential absorption

Question 12

What is the effect of Compton Scattering?

Answer 12

X-rays scatter away from the primary source to other people in the room or may fog the x-ray film.

Question 13

What will increase scatter?

Answer 13

Higher kV, increased thickness, increased density, decreased collimation

Question 14

What does mA affect?

Answer 14

current to the cathode - electron cloud - the number of x-rays

Question 15

What does the seconds control affect?

Answer 15

How long the electrons flow

Question 16

What does increase in kV do to the x-ray?

Answer 16

Increased penetration, decreased contrast, increased scatter

Question 17

Define radiographic density and list which factors contribute to it

Answer 17

The blackness of the film - determined by the number of photons reaching the plate - all factors (kV, mA, s) contribute

Question 18

Describe the contrast of an image with few shades of grey

Answer 18

High contrast

Question 19

Describe the contrast of an image with many shades of grey

Answer 19

Low contrast

Question 20

Which exposure factor controls contrast?

Answer 20

kV

Question 21

What are the main things to assess a radiograph for in practice?

Answer 21

positioning, density, detail and distortion

Question 22

What factors affect contrast?

Answer 22

kV, object thickness and density, scattered radiation, film processing

Question 23

What is radiographic detail?

Answer 23

the degree of definition or clarity

Question 24

What factors affecat radiographic detail?

Answer 24

focus to film distance, object to film distance, movement blur, focal spot size, film screen combination, scatter

Question 25

How can you control the area exposed?

Answer 25

Collimation

Question 26

What is a grid?

Answer 26

a device placed between the patient and the film to absorb scatter

Question 27

What are the 3 functions of a cassette?

Answer 27

light proof box, ensures intimate contact between the film and screens, transforms x-rays to light

Question 28

Where are intensifying screens found and what are they made up of?

Answer 28

inside the cassette, made of layers of phosphor crystals that adsorb x-ray energy and convert it to visible light