Medical X-rays

Question 1

What is electric charge measured in?

Answer 1

Coulombs (C)

Question 2

1 Coulomb is the magnitude of..

Answer 2

the electrical charge in 6.24 x10^18 electrons

Question 3

Electricity is a form of energy related to..

Answer 3

the flow of electric charges

Question 4

Voltage equation =

Answer 4

Work done (or potential energy change) divided by charge

Question 5

Current equation =

Answer 5

charge passing through area divided by time

Question 6

Unit for current

Answer 6

coulomb per second or ampere (A) - shortened to amps

Question 7

Power =

Answer 7

the rate of consumption of electrical energy

Question 8

power unit

Answer 8

watt (W)

Question 9

Watt equation =

Answer 9

V x A

Question 10

Resistance of a material

Answer 10

the opposition to the passage of electric charge

Question 11

Ohm’s law equation

Answer 11

A = V / R

Question 12

Resistors

Answer 12

devices that resist the free flow of electric current through them

Question 13

Transistors

Answer 13

Devices whose functions inc switching, voltage/current regulation, and amplification

Question 14

Capacitors

Answer 14

devices which store electric charge

Question 15

Diodes

Answer 15

Devices with low resistance to current flow in one direction, and high resistance in the other

Question 16

Current direction

Answer 16

electrons flow from negative to positive

Question 17

To produce x-rays

Answer 17

Inside the x-ray tube the electrons are jumping from one section to another without a wire. within the x-ray tube that x-rays are produced and emitted.

Question 18

What’s the x-ray tube

Answer 18

essentially a massive valve, or switch, completing an electric circuit, and consists of a cathode and an anode enclosed in a vacuum.

Question 19

Cathode

Answer 19

Negatively charged side of the x-ray tube (next to focusing cup)

Question 20

Filament

Answer 20

Very tightly wound coil of wire (usually made of tungsten)

Question 21

When an electric current is passed through, it heats up to such an extent that…

Answer 21

some of the electrons have enough energy to break free (thermionic emission)

Question 22

number of electrons emitted from the filament is directly proportional to..

Answer 22

the amount of electrons flowing inside it

Question 23

as negative electrons repel each other, the electrons that have been emitted have a tendency to..

Answer 23

spread out in different directions

Question 24

what is a focusing cup?

Answer 24

a negatively charged housing that directs the electrons to stay together

Question 25

the force is overpowered by the repulsive force of the focusing cup and the electrons...

Answer 25

tend to converge rather than diverge

Question 26

anode

Answer 26

positively charged (so it attracts electrons)

Question 27

the anode consists of

Answer 27

a flat circular disc that acts as the target for the stream of electrons that are emitted from the cathode

Question 28

what happens when the electrons hit the anode

Answer 28

they slow down very fast and lose lots of energy very quickly

Question 29

99% of energy lost is in the form of

Answer 29

heat

Question 30

1% of energy loss is in the form of

Answer 30

X-rays through the bremsstrahlung process

Question 31

what is the bremsstrahlung process?

Answer 31

radiation produced by the deceleration of an electron passing through a nucleus

Question 32

what happens if electrons are fired through a space containing any gas?

Answer 32

electrons interact by colliding with gas molecules and producing lower secondary electrons

Question 33

why are lower secondary electrons not desirable in an x ray tube

Answer 33

as they make the quantity and quality of x-rays produced very difficult to control

Question 34

because of lower secondary electrons, x-ray tube requires...

Answer 34

a vacuum environment, maintained by an airtight glass enclosure

Question 35

what does oil do in the vacuum environment

Answer 35

cools the apparatus

Question 36

what is in the tube housing

Answer 36

oil, tube, electrical connections and a small window at the bottom

Question 37

what does the small window at the bottom of the tube housing do?

Answer 37

allows x-rays to leave

Question 38

what is tube housing lined with

Answer 38

lead

Question 39

what does the lead around the tube housing do?

Answer 39

prevent stray x-rays from escaping

Question 40

what happens when you increase the current flowing through an x-ray tube?

Answer 40

increases the number of electrons which are flowing around the circuit, so the number of x-rays generated would increase

Question 41

what happens when you increase the voltage?

Answer 41

the photons which make the x-rays will have more energy and the x-rays will be more penetrating

Question 42

whats the target area

Answer 42

the area where the x-rays hit after leaving the x-ray tube through the window

Question 43

what are the x-rays generated by

Answer 43

the anode

Question 44

where do the x-rays leave

Answer 44

a point directly above the window of the tube housing

Question 45

variable amounts of the x-ray beam that passes through body tissue depends on...

Answer 45

the composition and thickness of the tissues and the strength of the beam

Question 46

magnitude of this variation in intensity mechanism

Answer 46

x-ray beam emanating from the patient produces diagnostic info

Question 47

the info content of this x-ray image must be transformed into..

Answer 47

a visible image with minimal info loss

Question 48

the higher the kV in the x-ray tube the...

Answer 48

the more penetrating the x-rays are, although the amount of scattering increases

Question 49

the lower the kV the...

Answer 49

the less penetrating the x-rays are, although there is less scattering and thus more contrast between bone and soft tissue

Question 50

for thick body sections like the abdomen, it's necessary to use

Answer 50

a high number of kV to allow significant radiation to pass through the patient's body and register on the x-ray image

Question 51

for bony structures with finer detail like a and radiograph, you need

Answer 51

low kV

Question 52

what happens if you use an incorrect number of kV

Answer 52

poor quality image is produced

Question 53

amount of darkening of an x-ray image is quantified by...

Answer 53

the optical density D

Question 54

optical density equation

Answer 54

D = log i0/it

Question 55

i0 =

Answer 55

the intensity of light before it passes through the image (incident radiation)

Question 56

it =

Answer 56

the intensity of light that has passed through the image (transmitted radiation)

Question 57

a good radiograph should have optical density between

Answer 57

2 and 4

Question 58

if D < 2 then...

Answer 58

the image is too bright

Question 59

if D > 4

Answer 59

the image is too dark