RADT 334 UNIT 4

Electrons emitted by the filament and directed to the target (traveling from the cathode to the anode)

projectile electrons

The strength of attachment of electrons to the nucleus

binding energy

X-rays produced by transitions of orbital electrons from outer to inner shells

characteristic x-rays

X-rays produced by interaction of a projectile electron with the nuclear force field of a target nucleus

bremsstrahlung x-rays

X-ray intensity, measured in milliroentgens (mR) or air KERMA (mGy)

x-ray quantity

Effective energy of the x-ray beam; penetrating ability

x-ray quality

The monoenergetic equivalent of an x-ray beam

effective energy

Section of metal added to the x-ray tube housing. Overall result is an increase in the effective energy of the x-ray beam (higher quality) and an accompanying reduction in x-ray quantity. Results in reduced patient radiation dose.

added filtration

The measure of x-ray energy of all x-rays, a graphical representation of the relative quantities of photons of each type of energy in the x-ray beam

emission spectrum

The x-ray tube target material principally used for mammography

molybdenum

Calculate the energy of the characteristic x-ray produced when a K-shell electron is replaced by an M-shell electron in tungsten

66 keV

At what fraction of the velocity of light do 90 keV electrons travel?

60%

What does the discrete x-ray spectrum represent?

characteristic x-rays

when an x-ray imaging system is operated at 80 kVp, its emission spectrum represents an output intensity of 3.5 mR/mAs. What will be the output intensity if the voltage is increased to 90 kVp?

4.42 mR/mAs

How will the emission spectrum change if going from 80 kVp to 90 kVp?

higher amplitude and shifts to right

What will happen to the x-ray emission spectrum if you change your imaging system from single phase to three phase?

higher amplitude and shift to right

How will the x-ray emission spectrum be changed if you add filtration to the x-ray tube?

lower amplitude and shift to right

How is the kinetic energy of the projectile electrons streaming across the x-ray tube increased?

increase kVp

Why is the x-ray tube considered an inefficient device?

only 1% of projectile electrons are converted into x-rays

What is the importance of K-characteristic x-rays in forming a diagnostic radiograph

Significantly helpful when the kVp is about 70 kVp(the K shell binding energy for tungsten)

What is the range of energies of bremsstrahlung x-rays?

From near zero to an energy in keV equal to the kVp

Name the factors that affect the shape of the x-ray emission spectrum.

Voltage, rectification, filtration, tube current

What is the 15% rule?

A 15% increase in kVp is equivalent to doubling the mAs

What is the diagnostic range of x-rays?

20-150 kVp

The filtration provided by the window and oil bath of the x-ray tube

inherent filtration

The unit of x-ray quantity

Milliroentgen (mR) or milligray (mGy)

Addition of a filter shifts the x-ray emission spectrum to the high-energy side, resulting in an x-ray beam with higher effective energy, greater penetrability, and higher quality, but less intensity

filtered x-ray spectrum

A kVp change equal to twice the mAs

15%

three filter materials used with diagnostic x-ray beams

Aluminum, molybdenum, rhodium

The thickness of filter or other absorbing material that will reduce intensity to half its original value

HVL

A compensating filter designed to shape the useful x-ray beam to the anatomic structure under examination so that the exposure of the image receptor will be more uniform

wedge filter

Identified numerically by half-value layer; also influenced by kVp and the added filtration in the useful beam

unit of x-ray quality

The approximate HVL of your x-ray imaging system

Usually totals 2-3 mm of aluminum equivalent

Another term for x-ray quantity, measured in mR or mGy

x-ray intensity

An abdominal radiograph taken at 84 kVp, 150 mAs results in patient radiation exposure of 650 mR. The image is too light and is repeated at 84 kVp, 250 mAs. What is the exposure?

1083 mR

An image of the lateral skull taken at 68 kVp, 20 mAs has sufficient optical density but too much contrast. If the kVp is increased to 78 kVp, what should be the mAs?

100 mAs

A chest radiograph taken at 180 cm SID results in an exposure of 12 mR. What would the exposure be if the same radiographic factors were used at 100 cm SID?

38.9 mR

Old technique: 60 kVp, 10 mAs= 28 mR New technique: 55 kVp, 10 mAs = what new intensity?

23.5 mR

The kVp is reduced from 78 to 68 kVp. what should be done to the mAs to maintain the same exposure of the the image receptor?

double the mAs

What is the relationship between x-ray quantity and mAs?

directly proportional

List two ways x-ray beam can be shifted to a higher average energy?

Increase kVp or added filtration

Why is aluminum used for x-ray beam filtration?

Because it is efficient at removing low-energy x-rays, and because it is readily available, inexpensive, and easily shaped into filters

Describe the use of a wedge filter during a foot x-ray

The thicker part of the wedge should be positioned toward the toes in order to equalize optical density.

Does adding filtration to the x-ray beam affect the quantity of x-rays reaching the image receptor?

Yes

Effect of increasing mAs on x-ray quality?

none

Effect of increasing mAs on x-ray quantity?

increase

Effect of increasing kVp on x-ray quality

increase

Effect of increasing kVp on x-ray quantity

Increase

Effect of increasing distance on x-ray quality

none

Effect of increasing distance on x-ray quantity

decrease

effect of increasing filtration on x-ray quality

increase

Effect of increasing filtration on x-ray quantity

decrease

The relationship among transmitted x-rays, photoelectrically absorbed x-ray, and Compton scattered x-rays resulting in the x-ray image

differential absorption

Scattering of very low energy x-rays with no loss of energy; also called coherent or Thompson scattering

classical scattering

The quantity of matter per unit volume, usually specified in kilograms per cubic meter (kg/m3) Sometimes reported in grams per cubic centimeter (gm/cm3)

mass density

The threshold energy required by a photon to undergo pair production

1.02 MeV

A high atomic number material (for example, iodine and barium), or a low density, low atomic number material (air) administered in liquid or gas form to improve the contrast resolution of an x-ray examination

contrast agent

X-ray ionization resulting in x-ray scattering

Compton effect

The reduction in x-ray beam intensity as a result of photoelectric absorption and Compton scattering

attenuation

having a single energy. Characteristic x-rays are monoenergetic, and the effective x-ray energy of an x-ray beam is the monoenergetic equivalent of the actual beam

monoenergetic

Electrons released in ionization as the result of photoelectric interaction and Compton scattering

secondary electron

An x-ray absorption interaction in which the x-ray is not scattered but totally absorbed. A photoelectron is is then released from the atom.

photoelectric effect

What are the two factors of importance to differential absorption?

KeV and atomic number of absorber

1000 x-rays with energy of 140 keV are incident on bone and soft tissue of equal thickness. If 87 are scattered in soft tissue, approximately how many are scattered in bone?

87

why are iodinated compounds such excellent agents for vascular contrast examinations?

high atomic number and high mass density

Compton scattered x-rays leave the scattering object in the approximate direction of the incident x-ray beam.

backscatter radiation

Which 3 of the 5 basic mechanisms of x-ray interaction with matter are not important in diagnostic radiology?

Classical, photodisintegration, pair production

Why are there 3 mechanisms of x-ray interaction with matter that are not important in diagnostic radiology?

the x-ray energies involved are outside of the diagnostic energy range

Does the probability of the Compton effect depend on the atomic number of the target atom?

No

When kVp is increased, is Compton scattering increased or reduced?

increased

How much more likely is it that an x-ray will interact with bone than with muscle?

(13.8/7.4)3=6.5

What is the relationship between atomic number and differential absorption?

Differential absorption resulting from photoelectric effect is proportional to the third power of the atomic number. Compton effect is unrelated to atomic number.

What is the relationship between mass density and differential absorption>

The probability of interaction is proportional to mass density, and therefore, so is differential absorption.

What kVp is used to penetrate barium in a contrast examination?

90 kVp