Physics: X-Ray Production 2 (Huda)

Front 1

What is bremsstrahlung radiation

Back 1

Bremsstrahlung (braking) x-rays are produced when incident electrons interact with
nuclear electric fields, which slow them down (brake) and change their direction.

Front 2

What does bremsstralung radiation look like

Back 2

Front 3

Schematic of a bremstruhlung radiation

Back 3

Front 4

What does the bremsstrahlung spectrum look like

Back 4

Front 5

How is the energy of an xray determined from the bremsstrahlung radiation

Back 5

The closer the electron passes to the nucleus, the greater the interaction of the inci-
dent electron with the nucleus, and the higher the energy of the resulting x-ray.

Front 6

How does the realease of X-rays from characteristic X-ray work

Back 6

Front 7

FIG. 2.3. Characteristic radiation is produced when an incoming electron (1) interacts with an
inner-shell electron (2) and both are ejected (3). When one of the outer-shell electrons moves
to fill the inner-shell vacancy, the excess energy is emitted as characteristic radiation (4).
Sometimes the excess energy is emitted as an Auger electron (5) rather than as characteristic
radiation.

Back 7

FIG. 2.3. Characteristic radiation is produced when an incoming electron (1) interacts with an
inner-shell electron (2) and both are ejected (3). When one of the outer-shell electrons moves
to fill the inner-shell vacancy, the excess energy is emitted as characteristic radiation (4).
Sometimes the excess energy is emitted as an Auger electron (5) rather than as characteristic
radiation.

Front 8

What are characteristic X-rays

Back 8

Front 9

What does x-ray intensity refer to

Back 9

Intensity refers to the quantity or number of x-ray photons produced.

Front 10

Name 3 factors that affect x-ray intensity

Back 10

-Intensity is affected by the generator type, beam filtration, and distance from the
beam (inverse square law).

Front 11

What percent of X-ray intensity is from characteristic radiation

Back 11

10%

Front 12

What is X-ray output proportional to

Back 12

X-ray output is directly proportional to the current (mA), and to exposure time (sec-onds).

Front 13

What is tube current and exposure time known as

Back 13

Th e product of the tube current (mA) and exposure time (seconds) is known as the
mAs, and the x-ray tube output is proportional to the mAs.

Front 14

What are 2 ways of doubling the mAs

Back 14

-Doubling the current at constant exposure time has the same effect as doubling the
exposure time at constant tube current.

Front 15

How does doubling the mAs effect the energy spectrum

Back 15

Doubling the mAs doubles the number of x-rays emitted but does not change the
energy spectrum

Front 16

What happens to the quantity of x-rays produced when the kVp is increased

Back 16

The quantity of x-rays produced can also be increased by increasing the kVp, but this also changes the quality or shape of the x-ray spectrum

Front 17

Does increasing kVp increase the quantity

Back 17

yes and will increase the energy

Front 18

What is intensity synonomous with

Back 18

quantity

Front 19

What is increased by increasing the kVp

Back 19

intensity (quantity) of x-rays
energy (increased quality)

Front 20

What is increased with increasing mAs

Back 20

quantity (intensity)

Front 21

What are 2 ways to increase the quantity (intensity)

Back 21

increase mAs or kVp

Front 22

Whe n the mA is increased and the
peak voltage and exposure time are constant, the intensity of the x-rays increases but the en-ergy distribution stays the same

Back 22

Front 23

Whe n peak voltage is increased and the milliamperes and
exposure time are constant, the intensity, peak, and mean energy of the x-rays increase

Back 23

Front 24

What is the tube potential proportional to

Back 24

Th e quantity (intensity) of x-ray production is approximately proportional to the
square of the tube potential.

Front 25

What is meant by polychromatic X-rays

Back 25

X-ray beams in diagnostic radiology are polychromatic and consist of a range of
photon energies

Front 26

What does the term quality X-rays mean

Back 26

Quality refers to effective photon energy of the x-rays produced, and relates to their
ability to penetrate the patient.

Front 27

How is the quality of an X-ray beam obtained

Back 27

Th e quality of an x-ray beam is obtained from the effective x-ray energy of the x-ray spectrum

Front 28

What is the range of effective photon energy

Back 28

Th e effective photon energy is taken to be between one third and one half of the
maximum photon energy.

Front 29

What does increasing the kVp do

Back 29

Increasing the peak voltage (kVp) increases the x-ray tube output, peak energy,
and mean energy of the beam.

Front 30

What is kVp

Back 30

peak voltage

Front 31

What does increasing beam quality do to penetrating power

Back 31

-Increasing beam quality increases x-ray beam penetrating power because the av-erage photon energy is higher.

Front 32

What are the relative effects on film density between kVp and mAs

Back 32

A rule of thumb is that increasing the peak voltage by 15% has the same effect on
film density as that of doubling the mAs.

Front 33

What does reducing the voltage waveform ripple do to the average photon energy

Back 33

Reducing the voltage waveform ripple increases average photon energy and thus x-ray beam quality

Front 34

What is ripple

Back 34

A constant high voltage is desired across the x-ray tube for x-ray production, but in
practice, there is some variation in the voltage, which is called ripple.

Front 35

What does voltage ripple look like

Back 35

Front 36

What does a X-ray tube look like

Back 36

Front 37

What is this image demonstrating

Back 37

The magnified view of the target illustrates the line focus principle, whereby
the focal spot size (F) is smaller than the electron beam (L) because of the anode angle.

Front 38

What is the electron source of the x-ray tube

Back 38

X-ray tubes contain a negatively charged cathode containing the filament that
serves as an electron source.

Front 39

Where are the X-rays produced in the X-ray tube

Back 39

Th e anode is positively charged and includes the target where x-rays are produced.

Front 40

Why is the x-ray tube in an evacuated envelope

Back 40

Th e anode and cathode are contained in an evacuated envelope to prevent the elec-trons from colliding with gas molecules.

Front 41

What is the function of the X-ray tube housing

Back 41

Th e envelope is contained in a tube housing that protects and insulates the tube and
provides shielding to prevent leakage radiation.

Front 42

What part of the tube housing helps in cooling

Back 42

Th e housing contains an oil bath to provide electrical insulation and help cool the
tube.

Front 43

What are anodes made of

Back 43

tungsten

Front 44

Do some anodes have 2 focal spot sizes

Back 44

yes

Front 45

What is a focusing cap

Back 45

A focusing cup or cathode block surrounds the filament and helps direct the elec-trons toward the target.

Front 46

What does a focusing cap look like

Back 46

Front 47

What does expulsion of electrons from the cathode look like

Back 47

Front 48

What causes electrons to be released by the cathode filament

Back 48

Electrons that flow through electrical circuits cannot generally escape from the conductor material and move into free space. They can, however, if they are given sufficient energy. In a process known as thermionic emission, thermal energy (or heat) is used to expel the electrons from the cathode. The filament of the cathode is heated in the same way as a light bulb filament by passing a current through it. This heating current is not the same as the current flowing through the x-ray tube (the MA) that produces the x-radiation. During tube operation, the cathode is heated to a glowing temperature, and the heat energy expels some of the electrons from the cathode.

Front 49

What causes the temperature to increase in the cathode

Back 49

Th e high resistance in the filament causes temperature to rise (>2200°C), resulting
in the thermionic emission of electrons.

Front 50

What is the negative cloud surrounding the cathode called

Back 50

Electrons emitted from a heated filament form a negative cloud around the filament
called a space charge, which prevents further emission of electrons.

Front 51

What is the tube current

Back 51

Electrons emitted from a heated filament form a negative cloud around the filament
called a space charge, which prevents further emission of electrons.

Front 52

What is the range of tube current

Back 52

Tub e current is in the range of 1 to 1,000 mA.

Front 53

What occurs to the cathode at low peak voltage

Back 53

A t low peak voltage, the potential is insufficient to cause all the electrons to be pulled
away from the filament, and a residual space charge remains (space charge limited
operation).

Front 54

What occurs a saturation voltage

Back 54

A t the saturation voltage, all electrons are immediately pulled away from the fil-ament, and the tube current is maximized.

Front 55

What is the high voltage created by the generator used for

Back 55

to accelarate the electrons as they move from the cathode to the anode

Front 56

What is the typical voltage across the cathode filament itself (different then previous)

Back 56

Typical voltages across the x-ray tube filament are 10 V, and currents through
the cathode filament are 4 A.

Front 57

How much power is dissipated by the cathode filament

Back 57

Th e power dissipated from the filament (I x V) is typically 40 W

Front 58

What does the x-ray tube and generator working in tandem look like

Back 58

Front 59

What do characteristic lines look like on an X-ray spectra

Back 59

Front 60

If the kVp is low do we see characteristic lines

Back 60

no

Front 61

If the kVp is low do we see characteristic lines

Back 61

no

Front 62

What is the voltage waveform chart

Back 62

Front 63

How is peak voltage demonstrated

Back 63

not that more x-rays are produced at peak voltage

Front 64

In an X-ray tube how is Voltage and kVp and keV related

Back 64

In the x-ray tube, electrons are generated at the filament end of the x-ray tube by thermionic emission (boiling of electrons from the filament). They are then given kinetic energy by applying a high voltage between the filament and the target. If a voltage of 100,000 volts (100 kVp) is applied to the x-ray tube, the electrons will strike the target producing x-rays with energies from 0 to 100 keV. Note: kVp is the voltage applied to the x-ray tube and keV is the energy of the x-ray. The low energy x-rays can not get out of the x-ray tube so the actual spectrum of x-rays range from about 10 keV to 100 keV. The higher the x-ray energy, the higher its ability to penetrate tissue. As the kVp increase so does the intensity of the x-ray beam, i.e. more x-rays of all energies are generated. (ignore picture)