X-Ray Module 6

What are the basic possible outcomes for an incident X-ray?

Absorption

Transmittance

Scatter

An X-ray image is the result of what?

Difference between x-rays absorbed and x-rays through image receptor

What percentage of incident x-rays reach the image receptor?

1

Which X-ray interactions occur in diagnostic range?

Coherent scattering

Compton effect

Photoelectric effect

What are all the X-ray interaction with matter?

Coherent scattering

Compton Effect

Photoelectric Effect

Pair production

Photodisintegration

Which X-ray interactions contribute significantly to the image?

Compton effect

Photoelectric effect

What is the alternative name for coherent scattering?

Thompson scattering

Classical scattering

What energy does coherent scattering typically occur?

Below 10 keV

What does the coherent X-ray interact with?

Atom and excites it

What are the properties of the new x-ray in coherent scattering?

Same energy and wavelength

Direction changes

What is transmittence?

Goes right through patient

What is scatter?

X-ray deviates

How does scatter affect the image?

Image noise

Reduced clarity

When causes the compton effect?

X-ray interacts with an outer-shell electron

What are the characteristics of the compton effect?

New energy (lower)

New direction

What is the probability of the compton effect?

Inversely proportional to the energy of the X-ray

Higher X-ray energy = Compton effect less likely

When will Compton effect occur?

Energy of an incident X-ray is greater than the binding energy of an electron

More likely in loosely bound, outer shell electrons

T/F: The atomic number of the absorbing tissue will have an affect the probability of the comton effect.

False

What is the result of comton effect?

Reduce image contrast

No useful information

What is the term for when a compton scattered X-ray deflects 180 degrees?

Backscatter radiation

When is photoelectric effect likely to occur?

X-rays interact with inner-shell electrons

What is the end result of the photoelectric effect?

Total absorption

Creates shadow

Becomes ionized

What is the probability that an X-ray will undergo the photoelectric effect?

Directly proportional to the 3rd power of the atomic number of the absorbing material

What is the only way a photoelectric interaction will occur?

Incident X-ray has equal or greater energy than electron binding energy

What is the probability that an X-ray will undergo a photoelectric effect?

Inversely proportional to the 3rd power of the X-ray energy

1/E³

Less likely with high energy x-rays

What does the photoelectric effect produce in the image?

Light (white) areas

What is a pair production?

Interacts with the nucleus of an atom and not electrons

What is produced during pair production?

2 electrons

One positive, one negative

What is the required energy for pair production?

1.02 MeV

What occurs if the energy is above 10MeV?

Can be absorbed directly by nucleus

Nucleus raised to excited state, emits nucleon

What is mass density?

Quantity of matter per unit volume

Kg/m³

What is the result if the mass density is doubled?

Chance of X-ray interaction is doubled

What is attenuation?

Reduction in total number of x-rays passing through

What creates the darker areas of the image?

Higher exposure

What creates the lighter areas of the image?

Lower exposure

What is optical density?

How dark the overall image is

What does more exposure affect hard copy film?

Darker image

What can be manipulated in digital systems?

Optical density

Which kind of x-rays does quantum mottle occur?

Digital

What is quantum mottle?

Random fluctuations in optical density (noise) due to lack of information

Few photons = more quantum mottle

What is dose creep?

Unnecessarily increase dose with digital imaging

What is exposer index? (EI)

Measure of amount of exposure received by image receptor

What is the exposure index dependent on?

mAs

Total detector area irradiated

Beam attenuation

What is contrast?

How many shades of grey there are

What is the result of high contrast?

Fewer shades of grey

What is the result of low contrast?

Many shades of grey

What hard copy imaging, what primarily influences contrast?

kVp

How will kVp influence contrast in digital?

Less directly

Less significantly

How will raising kVp by 15% impact the x-rays?

Double # of x-rays

(15% rule)

What will altering the kVp affect in hard copy?

Contrast

Optical density

How will kVp affect contrast?

1/kVp

Higher kVp = lower contrast

How do you maintain exposure when increasing kVp by 15%

mAs should be lowered by ½

15% = ½ , 30% = ¼ , 60% = 1/8

What will result be in increasing kVp by 15% and mAs by 1/2?

Same number of X-rays, higher average energy

Dose saving

What is the trade off for dose saving with 15% kVp and ½ mAs?

Reduced range of intensities that reach image receptor

What is latitude?

Measure of range of exposures that may be reproduced for a given imaging system

What is alternative name for latitude?

Dynamic range of a system

What is Source to Image-Receptor Distance? (SID)

Distance from anode to image receptor

What results in increasing SID?

Increase in quantum mottle in digital