LEC 1 - Radiology Principles Flashcards by Raegan Chambers

What are the five main parameters for xray?

Grid 
Focus 
mAs 
Field size 
kVp

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What are the two things that happen to an xray when it interacts with matter?

Absorption
– or –
Scatter

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How are x-rays produced?

Conversion of kinetic energy of accelerated electrons into alectromagnetic radiation

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What 3 major things happen with electrons in the x-ray tube?

Production + Acceleration + Deceleration

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What is the source of the electrons?

Cathode

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Where does deceleration occur?

Anode

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What two forms of energy are the electrons converted into?

X-rays
– and –
Heat

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What form of energy is created most in the process of producing xrays?

Heat

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What is the cathode made from?

Tungsten

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How are electrons focused in an x-ray?

Negatively charged metal housing

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Term: mA

X-Ray tube current

Number of electrons flowing per second from filament to target

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What is the problem with increasing mAs?

Increased time of exposure
= increased motion in image
= decreased quality

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What technically is occurring when you increase mAs?

Number of electrons accelerated increases

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What is potential difference?

kVp

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What does a high potential difference lead to?

Accleration of electrons in vacuum towards anode

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What happens when high speed electrons strike anode?

Radiation emitted

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What are the two methods that radiation are emitted from an anode?

Characteristic radiation
– and –
Bremsstrahlung

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What part of energy do you want to filter out of your xray?

low energy

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What is occurring with Bremsstrahlung?

Incident electrons are deflected around nucleus
Loss of energy emitted = xray

– or –
Incident electrons hit nucleus = high energy

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What happens if you increase kVp too much?

Too much exposure = xray looks black

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What is occurring with characteristic radiation?

High speed electron hits electron in orbit

= x-ray photon given off

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What settings (basic) do you want for lung and abdomen xrays?

increased kVp + decreased mAs

- Gray

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What settings (basic) do you want for constract/bone xrays?

increased mAs + decreased kVp

- Black/white

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What exactly happens when you increase kVp?

Increase electron velocity
Increase x-ray energy
Increase penetrating power

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What are the two stages of an xray?

Rotation -- and -- Exposure

What are the characteristics of a small filament?

Small electron beam + focal spot | Fine detail, concentrates heat

What are the characteristics of a large filament?

Larger electron beam + focal spot | Reduced detail, but higher exposure (mAs)

What does the angle of the anode cause?

Heel effect

What is the heel effect?

What % of intesity changes as it moves away from the central ray

Where is the % of intensity the highest?

Near the cathode

Why is the anode side of the x-ray weak?

It has to travel through part of the machine before it reaches the patient

Where do you want the cathode anatomically when taking xrays?

Proximal

Term: Attenuation

Decrease in intensity of x-ray beam as it passes through matter

Term: Absorption

Photon removed from beam

Term: Scatter

Photon changes direction

Term: Transmission

X-ray passes through matter without interaction

Term: Shadowgram

attenuation through different tissues in patient changes intensity producing a picture on the xray

Term: Quality of a Beam

Penetrating power | Proportional to x-ray enerygy

Term: Intensity of a Beam

Amount of energy in beam | Proportional to number of photons

What are the types of scatter that can occur in an x-ray?

Coherent + Photoelectric effect + Compton

What is the most important scattering effect that occurs with x-rays?

Photoelectric effect

What does coherent scattering cause on the film?

Film fog

What does the photoelectric effect cause on the film?

Contrast

What does compton scattering cause on the film?

Film fog + Increase in hazards

What is coherent scattering?

Photon interacts with object + changes direction

Term: Film fog

Decrease in radiographic quality

Wha tis the photoelectric effect?

Complete absorption of the x-ray photon | Photoelectron removed from shell = IONIZATION

What are the factors that determine the probability of PE occurring?

Atomic number -- and-- Inversely proportional to x-ray energy cubed

What scenario is PE most likely to occur?

Low energy photon + High atomic number

What does PE do?

Magnifies the differences in the tissues | = increased contrast

What is the compton effect?

Incoming photon ejects free outer shell electron | Photon scatter = lower energy but can produce ionization

What are the factors that determine the probability that the Compton effect will occurr?

Energy of photon -- and -- Electron density (NOT ATOMIC NUMBER)

What is the major result of the Compton effect?

Almost all scatter reaches the film

What kind of contrast is seen with low kVp

High contrast

What are the four factors that determine the degree of x-ray absorption?

Atomic number of tissue Density of tissue Thickness Photon energy

What are the components of radioopacity?

Effective Z -- and -- Density

What are the five radiopacities? (in order)

``` (lucent) Air Fat Soft tissue bone Metal (Opaque) ```

Term: Scatter radiation

Radiation from sources other than primary x-ray beam

What scatter effect produces scatter radiation?

Compton

What are the three causes of scatter radiation?

Thick tissues Table Cassette

What are the three factors that influence scatter?

kVp Field size Tissue thickness

How is scatter production reduced?

Collimation via low kVp + tissue compression

How is the effect of scatter on film reduced?

Grids + Air gap

What are the tissues that tend to be the most responsive to xrays?

Bone marrow Epithelial GI

What effects do xrays have on gonadal cells?

Amplified damage due to genetic alterations

What effects do xrays have on fetal cells?

Death Congenital malformations Growth defects

What is the stochastic effect?

Probabilty of damage occurring increases with dose

What effect do xrays have during the first trimester?

Fetal death

What is the effect of xrays during the second trimester?

Developmental anomalies

What is the effect of xrays during the third trimester?

Delayed growth

At what point can you take pregnancy xrays of cats?

39 days

At what point can you take pregnancy xrays of dogs?

42 days

What is the inverse square law?

Distance from primary source is doubled | Intensity will decrease by a factor of four

What is the added filtration in an xray?

Aluminium

What is the inherent filtration in an xray?

Glass envelope Insulating oil Plastic tube window

Where do monitors for xrays need to be worn?

At collar level over apron -- and -- At waist level under apron