LEC 1 - Radiology Principles Flashcards
What are the five main parameters for xray?
Grid Focus mAs Field size kVp
What are the two things that happen to an xray when it interacts with matter?
Absorption
– or –
Scatter
How are x-rays produced?
Conversion of kinetic energy of accelerated electrons into alectromagnetic radiation
What 3 major things happen with electrons in the x-ray tube?
Production + Acceleration + Deceleration
What is the source of the electrons?
Cathode
Where does deceleration occur?
Anode
What two forms of energy are the electrons converted into?
X-rays
– and –
Heat
What form of energy is created most in the process of producing xrays?
Heat
What is the cathode made from?
Tungsten
How are electrons focused in an x-ray?
Negatively charged metal housing
Term: mA
X-Ray tube current
Number of electrons flowing per second from filament to target
What is the problem with increasing mAs?
Increased time of exposure
= increased motion in image
= decreased quality
What technically is occurring when you increase mAs?
Number of electrons accelerated increases
What is potential difference?
kVp
What does a high potential difference lead to?
Accleration of electrons in vacuum towards anode
What happens when high speed electrons strike anode?
Radiation emitted
What are the two methods that radiation are emitted from an anode?
Characteristic radiation
– and –
Bremsstrahlung
What part of energy do you want to filter out of your xray?
low energy
What is occurring with Bremsstrahlung?
Incident electrons are deflected around nucleus
Loss of energy emitted = xray
– or –
Incident electrons hit nucleus = high energy
What happens if you increase kVp too much?
Too much exposure = xray looks black
What is occurring with characteristic radiation?
High speed electron hits electron in orbit
= x-ray photon given off
What settings (basic) do you want for lung and abdomen xrays?
increased kVp + decreased mAs
- Gray
What settings (basic) do you want for constract/bone xrays?
increased mAs + decreased kVp
- Black/white
What exactly happens when you increase kVp?
Increase electron velocity
Increase x-ray energy
Increase penetrating power
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
