X-Ray Production, Target Interactions, & Xray Beam

Flashcards covering x-ray production steps, tube components, target interactions (Bremsstrahlung and characteristic), and fundamental properties of the x-ray beam.

What material is used for the anode target?

Tungsten anode

Which component of the rotating anode assembly is made of Molybdenum?

The neck and base

What are the four components required for x-ray production?

a. source of free electrons (e.g., thermionic emission), b. acceleration of electrons, c. focusing of electrons, d. deceleration of electrons

Which side of the x-ray tube is the cathode located on, and what is its charge?

Negative side of tube

What are the primary components that consist of the cathode?

Filament, focusing cup, and related wiring

What is the first function of the cathode?

Produce a thermionic cloud

How does the cathode interact with voltage?

Conduct the high voltage to the gap between the cathode and anode

What is the third function of the cathode during x-ray production?

Focus electron stream as it heads for the anode

What effect does increasing kVp have on the electrons in the x-ray tube?

Causes an increase in speed and energy of the electrons applied across the x-ray tube striking the anode

How does increasing kVp affect the quality and quantity of the x-ray beam?

Results in x-ray photons with greater energy (quality) and more interactions at the target (quantity)

What is the relationship between kilovoltage and the Half Value Layer (HVL)?

Direct relationship; as kilovoltage increases, HVL increases

What component is located between the incoming line and the exposure switch?

Autotransformer

During exposure, electrons are driven toward the anode target at what speed?

Half the speed of light

Approximately how far do electrons travel between the cathode and anode?

$$2\,cm$$

Why do electrons tend to diverge as they cross the tube?

Because they all have the same negative charge ($$-$)

What two factors help to focus the electron beam?

Low negative potential and geometry of the focusing cup

What is the space charge effect?

As more and more electrons build up, they begin to oppose the emission of any additional electrons

The space charge effect limits x-ray tubes to what maximum mA ranges?

$1,000$ to $1,200$

What is the charge of the anode side of the tube?

Positive

What are the common rotation speeds for an anode?

$3,000$ or $10,000\,rpms$

What are the three functions of the anode?

1. target surface and source of x-ray photons, 2. conducts high voltage back to circuitry, 3. primary thermal conductor

What are the two specific types of target interactions in the x-ray tube?

a. bremsstrahlung, b. characteristic

What percentage of the kinetic energy of incident electrons is converted to heat?

Over $99.8\%$

What items determine the type of interaction that will occur at the target?

Electron kinetic energy and the binding energy of the electron shells of the atom

List four common materials used for the x-ray target.

Tungsten, Rhenium, Molybdenum, Graphite

How is binding energy defined?

The energy required to remove an orbital electron from its shell

Which shell’s electrons possess the highest binding energy in any given atom?

K-shell electrons

How does atomic number affect K-shell binding energy?

Elements with a higher atomic number will have a higher K-shell binding energy

What is the relationship between electron distance from the nucleus and total energy?

Electrons further from the nucleus require less energy to remove (lower binding energy) and possess a greater total energy

If a term mentions an "incident electron," what process is being described?

X-ray tube interactions (Brems and Characteristic)

If a term mentions an "incident x-ray photon," what process is being described?

Interactions with tissue (Photoelectric absorption and Compton scatter)

What does the term Bremsstrahlung mean?

Braking or slowing

When does a Bremsstrahlung interaction occur?

When the incident electron interacts with the force field of the nucleus

What is emitted as an x-ray photon in a Brems interaction?

Lost energy from the electron slowing and changing direction

How is the energy of a Bremsstrahlung emission calculated?

It is equal to the difference between the entering and exiting kinetic energy of the electron

What range of energy can Bremsstrahlung photons have?

Total value of the incident electron (as high as peak kVp) down to unmeasurable amounts

What percentage of the x-ray beam is typically Bremsstrahlung?

$$70-90\%$$

When does a characteristic interaction occur?

Only when the incident electron interacts with an inner-shell electron (K-shell electron)

What threshold must an incident electron meet for a characteristic interaction to happen?

Must have enough energy to remove the inner-shell electron

What is the characteristic cascade?

When an electron from an outer shell drops into the hole created in the shell of an unstable atom

What produces the energy of a characteristic x-ray photon?

The energy difference between the inner and outer shell electron

What percentage of the x-ray beam is made up of characteristic interactions?

$$10-30\%$$

Below what energy level will characteristic interactions not happen in an atom of Tungsten?

Below $69.5\,kVp$

Is the quality of characteristic radiation dependent on the kVp selection?

No, it is dependent upon the binding energies of the target material

In what form do x-rays/electromagnetic radiation travel?

Sine waves

Identify the four characteristics of a sine wave.

1. Frequency, 2. Wavelength, 3. Velocity (speed), 4. Amplitude

How is frequency defined?

The number of wavelengths passing a point per second or the number of cycles per second

What is the unit of measurement for frequency?

Hertz ($Hz$)

What is the relationship between energy and frequency?

Direct relationship; Increase in energy = Increase in frequency

How is wavelength defined?

Distance from one crest to another, one valley to another, or distance between two successive points on the sine wave

What symbols and units are used to represent/measure wavelength?

Represented by lambda ($\lambda$) and measured in Angstroms ($\text{\AA}$) or meters

What is the relationship between wavelength and energy?

Inversely proportional; Increase in wavelength = decrease in energy

What is the velocity of all electromagnetic energies (the speed of light)?

$3.0 \times 10^8\,meters\,per\,second$ or $186,000\,miles\,per\,second$

What happens to frequency when wavelength is increased at a given velocity?

Frequency decreases

State the Electromagnetic Wave Equation.

$$c = f \lambda$$

What is the definition of x-ray quality?

A measurement of the penetrating ability of the x-ray beam

What numerical value is used to represent x-ray quality?

HVL (Half Value Layer)

What two factors directly affect x-ray quality?

kVp and filtration

Does mAs have an effect on x-ray quality?

No effect; mAs only affects quantity

How does filtration affect x-ray quality?

Increases quality by filtering out "soft" photons to create a beam with higher average energy

What is the definition of x-ray quantity?

A measure of the number of x-ray photons in the useful beam (primary beam)

What are three other terms used to describe x-ray quantity?

X-ray output, intensity, or exposure

What is the unit of measurement for x-ray quantity?

Roentgen ($R$)

Which factor is the primary controller of x-ray quantity?

mAs

How does increasing distance affect x-ray quantity?

Decreases quantity because x-ray photons spread out or diverge

How does filtration affect x-ray quantity?

Decreases quantity because it removes a portion of the useful beam

What is the primary or useful beam?

The beam that exits the tube

What is the remnant or exit beam?

The specific portion of the primary beam that remains after attenuation, exits the patient, and interacts with the IR

Most of the remnant radiation consists of what?

Scattered radiation

State the definition of the Inverse Square Law.

Radiation is inversely related to the square of the distance from the source

What is the formula for the Inverse Square Law?

$$\frac{I_1}{I_2} = \frac{D_2^2}{D_1^2}$$

Which factor has the greatest effect on patient dose?

SID (Source to Image Distance)

True or False: X-rays are electrically neutral.

True (not affected by electric or magnetic fields)

What terms describe the wide variety of energies and wavelengths in an x-ray beam?

Polyenergetic and heterogeneous

What path do x-rays take when traveling?

Straight lines

What is the effect of x-rays on certain crystals?

Cause fluorescence (emission of light)

Can x-rays be focused by a lens?

No

How do x-rays produce chemical and biological changes in matter?

Through ionization and excitation

What radiation is produced as a byproduct when x-rays pass through matter?

Secondary and scatter radiation

According to the transcript, x-rays travel at what speed in a vacuum?

$$3.0 \times 10^8\,meters\,per\,second$$