RAD 152: Unit 4

Anode Heat

• electrons in the outer shell are raised to an excited or higher energy level, electrons then immediately drop back to their normal energy level and emit (heat) infrared radiation

Anode Heat

Heat & mA have what type of relationship?

• direct relationship

Heat & kVp have what type of relationship?

• direct relationship

Binding Energy

• holds an electron in its orbit

Bremsstralung Radiation

• the closer the projectile electron gets to the nucleus, the more it is influenced by the nuclear electric field

• as the projectile electron passes by the nucleus, it is slowed down and its course changes

Bremsstrahlung Radiation

“braking” of projectile electrons

Characteristic Radiation

• occurs in the inner shell electron

• characteristic photons are emitted when an outer- shell electron drops to fill an inner shell

Characterisitc Cascade

• after an outer shell electron has been dropped to fill the”hole” another electron will drop to fill the “hole” it left 7 so on until only the outer most shell is missing an electron

K-Shell photons

• binding energy of 69.5 KeV

L,M,N Shell Photons

• have energy of 12 KeV

Characteristic Radiation

Continuous Emission Spectrum

• measures any type of x-ray emission occuring

Discrete Emission Spectrum

• measuring one type of x-ray emission

• characteristic x-rays have precisely fixed energies

Efficiency & kVp

• the efficiency of x-ray production increases with increasing kVp

Efficiency & mA

• efficiency of the x-ray production is independent of the tube current

Incident (projectile) Electron

• accelerated electrons that comprise the x-ray tube current

K- Characteristic X-rays

• require tube potential of at least 70 kVp to be produced

X- Ray Emission Spectrum

• a measurement tool used to determine the approximate frequency with which each x-ray interaction occurs

Emission Spectrum Shifts to the Right

• the higher the effective energy or quality of the x-ray beam

• kVp

Emission Spectrum Shifts to the Left

• the lower the effective energy of the x-ray beam

Emission Spectrum (large under the curve)

• higher the intensity or quantity of the x-ray beam

Emission Spectrum (small under the curve)

• lower the intensity of the x-ray beam

15% Rule (Part 1)

• increasing or decreasing the kVp by 15% has the same effect as doubling or halving the mAs

15% Rule (Part 2) (Altering or adjusting image exposure)

• Increase kVp 15%, the same mAs must be utilized—→ double mAs, the same kVp must be utilized

• decrease kVp 15%, the same mAs must be used—→ ½ mAs the same kVp must be used

15% (Part 3) (Maintaining Optical Density)

• Increase kVp by 15% with a reduction in mAs by ½

• Decrease kVp by 15% with doubing the mAs

Added Filtration

• Aluminum Sheets

• decreases intensity of x-ray beam & increases average energy (HVL)

Compensating Filtration

• Provides uniform image density for parts of varing thickness

Density

• the degree of blackening on the image

Filtration

• remove low energy (soft) x-rays from beam

• Increasing Filtration:

  • increases quality of an x-ray

  • decreases the quanity of an x-ray beam

Grid

• improves image contrast by absorbing scatter radiation produced in the pt before its able to reach the IR

• As grid ratio increases, the number of photons reaching the IR decreases

Half- Value Layer

• the thickness of absorber material necessary to reduce an x- beam to half of its original intensity

• describes x-ray quality

Inherent Filtration

• Window

• Dielectric Oil

Prime Factors

• kVp

• mA

• Exposure Time

• Distance

mAs Reciprocity

• the same radiographic density will result from different mA and time selections, provided that the mAs totals are equal

Total Filtration

• the total of both inherent and added filtration

Quality

• determined by kVp

Quantity

• determined by mAs and kVp

Three Primary Anose Target Interactions

1. Anode Heat

2. Characteristic Radiation

3. Brems Radiation

What produces low energy brems?

• created the projectile electron is barely influenced by the nucleus

• at larger distances from the nucleus (very little energy is lost)

What produces high energy brems?

• occurs when projective electron loses most if not all of its kinetic energy & drifts away from the nucleus

• at closer distances more energy is lost

Emission Spectrum (added filtration)

• causes spectrum to shift to the right

• decreases amplitude

The Discrete Portion of the Spectrum changes with?

• different target materials

mAs, kVp, and added filtration affect what on the emission spectrum?

• amplitude

kVp

• potential difference applied across the tube at the time the exposure is initiated

mA

• unit measuring tube current

Time

• determines the length of time tube produces x-rays

Distance

• affects the amount of radiation reaching the patient

Factors Affecting X-ray Quantity

1. mAs (directly related)

2. kVp(directly related)

3. distance (inversely related )

4. filtration (inversely related)

Factors Affecting X-ray Quality

1. filtration (directly related)

2. kilovolt peak (directly related)

Describe X-ray Quantity

1. intensity of beam

2. number of photons in a beam

3. measured in milligray

Describe X-ray quality

1. penetrability of the beam

2. how many photons will penetrate the anatomy

3. represented by HVL

kVp Controls what?

• beam quality

• amount of scatter

Increase in kVP

• more parts are penetrated

• longer scale of contrast

Decrease kVp

• more photons are absorbed in patient

• shorter scale of contrast

As SID increases

• beam intensity decreases

As SID decreases

• beam intensity increases

Monoenergetic

• beam that contains x-rays that all have the same energy

Heterogeneous

• beams that have different energy

Why is Aluminum a good filtration choice?

1. efficiently removes low energy x-ray

2. inexpensive

3. readily available

4. easily shaped

Purpose of Grid

• improve image contrast by absorbing scatter

• as grid ratio increases, the number of photons reaching the IR decreases