Exam 1 S2 Flashcards
Photoelectric effect strikes:
inner shell electron
In photoelectric effect the x-ray photon ceases:
to exist
In Photoelectric absorption the electron absorbs all:
the x-ray’s photon’s energy
In photoelectric effect the inner shell electron ____ ups &:
speeds (excites)
leaves the atom
In photoelectric effect the energy in excess of binding energy is given to:
the inner-shell electron
photoelectric effect is _____ likely to occur when the _____ of the incident x-ray is slightly ______ than the binding energy of the orbital electron
more
energy
higher
In photoelectric effect increased kVp leads to:
decreased photoelectric absorption
(Beam is too fast/intense)
In Compton scatter the x-ray photon ceases:
to exist
In Compton scatter some of the energy excess of binding energy is given to an:
outer shell electron
In photoelectric effect increased atomic number leads to increased
photoelectric absorption (attentuation)
(because more things to interact with)
In Compton scatter the electron absorbs:
all the incident x-rays energy
In Compton scatter _________ interacts (strikes) with an:
incident x-rays
outer shell electron
In Coherent when an incident x-ray interacts with an orbital electron it is:
Thompson
In Compton scatter outer shell electron speeds up and leaves:
what is this called?
the atom (recoil electron)
(Excess energy leaves as a scatter photon)
Attenuation can be affected by?
-Tissues thickness (every 4 cm = 50% xray beam attenuation)
-tissue atomic number (more z#= more attenuation)
-tissue density (most important ex: air vs muscle vs fat) muscle most dense/ air least dense
Both the photoelectric effect and compton scatter lead to
ionization
(the removal of an electron from orbit and net positive charge to the atom)
In Compton scatter remaining energy is ______ as a new x-ray and leaves the _____ in a random direction
reemitted
atom
In coherent scatter when an incident x-ray interacts with an entire atom is it called:
Rayleigh
Attenuation is?
What different interactions result in attenuation?
Reduction in the number/intensity of x-rays reaching the IR (through scatter/absorption)
Photoelectric (absorption)
Coherent scatter (absorption)
Compton (both scatter & absorption)
Compton scatter is proportionally more likely:
at high kVp levels
(this is bc higher kVp levels have lower absorption rate but compton remains consistent at all levels)
In coherent scatter the orbital electron reaches a temporary:
state of excitation
In coherent scatter when the energy of the incident photon is ______ than the ________ no ________ occurs
less
binding energy
ionization
mA is limited by what?
Focal spot size
mAs is a measurement of what?
it is considered:
what is it not?
electron flow in a conductor
an electrical term
a unit of radiation output
In coherent scatter the incident x-ray continues:
in a new direction
In coherent scatter no _____ occurs
energy transfer
mAs math:
100 mA and .5 sec
50 mAs
mAs is the primary controller of:
intensity/quanity in the remnant beam
Attenuation is absorption & scattering as a result of:
photoelectric effect
compton scatter
coherent scatter
How do we reduce motion?
setting the shortest time while maintaining same mAs output
(Shorter time requires more mA)
For each 4cm of tissue requires:
For every 4 cm of tissue how much x-ray beam attenuation is occuring?
doubling of mAs & kVp by:
15% kVp
100% mAs
- 50% x-ray beam attenuation
To calculate the mAs we:
multiply mA x Time
Radiologic time is measured in?
seconds
.25 secs or 250 ms or 1/4 second (all the same)
mAs math:
300 mA and .2 sec
60 mAs
(300 x .2)
Maintaining density:
150 mAs to 300 mAs
72 kVp to ___ ?
61.2 (reduced 15%, cuts exposure in half)’
mAs doubled
kVp needs to come down 15% to maintain
Doubling in mAs leads to:
doubling of intensity or quantity
What does kVp control?
the quality of the x-ray beam
mAs math:
200 mA and .2 sec
40 mAs
the small increase of 15% kvp will?
double the exposure to the image receptor
Kilovoltage is the measurement of
electrical force
What is penumbra?
Is it good or bad?
blurry or unsharp edges of the shadow or image
bad
when the kvp increases 15% patient exposure increases by:
1/3
kVp math:
increase kVp 15% of 70 kvp:
decrease kVp 15% of 100 kVp:
80.5 (70 x 1.15)
85 (100 x .85)
kVp means?
kilo voltage peak (the highest value in electrical generator)
What is remnant radiation?
the part of the x-ray beam that has passed through the patient
(Leftovers from the primary beam)
OID stands for?
object image distance (patient distance from IR)
What is preferred, optimal kVp or minimal kvp?
what is higher in kVp out of the 2?
optimal kVp
What does a higher kVp do?
increase the x-ray’s ability to penetrate through a particular tissue
SOD stands for?
Source to object distance (x-ray tube to patient)
SID stands for?
source to image distance (x-ray tube to IR)
What is umbra?
is the ‘‘pure” shadow or image of uniform darkness
(crisp shadow line)
What is elongation?
the object appears to be longer than its actual size
How much of the primary beam becomes remnant radiation?
less than 1%
What is shape distortion?
the difference between the actual shape of the object and the shape of its projected image
(Difference between actual object shapes
& the image shape)
What is distortion?
misrepresentation of the size or shape of an object
As a radiographer do we want pneumbra?
no, we want to minimize this
what is foreshortening?
the object appears to be shorter than its actual size
What is the relationship with SID and pneumbra & spatial resolution?
the greater the SID the smaller the pneumbra & higher the spatial resolution
What affects contrast?
kVp (low kvp = high contrast)
image receptor (grids)
computer algorithms (AEC)
patient factors (tissue density)
How do we calculate the mag factor?
dividing SID/SOD
How can we reduce shape distortion?
properly aligning the:
tube
(Object) part
Image receptor
How can size distortion (magnification) be reduced?
decreasing OID or
increasing SID
What is size distortion?
What is it also called?
misrepresentation of the size of the object
aka magnification
Mag Factor math:
An object that measures 6 cm is radiographed using SID of 48 and OID of 4. How many centimeters will the object measure on the completed radiograph?
6.54cm
(48 (SID) - 4 (OID) = 44 SOD
48 (SID) / 44 (SOD)= 1.09
1.09 x 6 cm= 6.54cm
What is spatial resolution?
What is also referred to as?
the sharpness of the structural edges around the image
AKA detail, sharpness, or decreased pneumbra (OR LOW BLUR)
Mag Factor math:
SID= 72
SOD=66
1.09 mag factor
How is resolution (spatial resolution) measured?
using a line-pair test tool
(measured in line-pairs per millimeter or LP/mm)
what affects spatial resolution?
motion
focal spot size
distance (SID, SOD, OID)
patient factors (OID or motion)
angulation (elongation/foreshortening)
What can contrast be referred to as?
which is?
gray scale
the number of different brightness levels in a x-ray
What is contrast?
the difference between 2 adjacent brightness levels
What can be used to increase subject (patient) contrast?
barium & iodine
Low contrast =
high contrast =
long scale (many greys)
short scale (black & white)
What is SNR?
What should it always be greater than?
Signal to noise ratio
one
What is noise?
undesirable image input that interferes with ability to visualize the x-ray
What is quantum mottle?
What is the opposite?
insufficient number of x-rays reaching the image receptor
scatter is too much x-rays reaching the image receptor
What causes quantum mottle?
What is usually the cause?
low mAs
low kVp
or difficult anatomy to penetrate
usually low technique, especially mAs
What is postprocessing?
adjustment of the image by a rad tech or rad at a workstation
More kvp = ____ scatter
more volume = _____ scatter more volume
more
more
(why collimation is key, and optimal kVp)
Low contrast =
High contrast=
Long scale & low kvp
Short scale & high kVp
What is window level?
What is window width?
post-processing of image brightness
post-processing if image contrast
For digital systems, what is preferred quantum mottle or scatter?
Scatter
(the digital systems are very good at filtering out too much information)
Low contrast =
High contrast=
Long scale & low kvp
Short scale & high kVp
What is the rule regarding tissues thickness?
for every 4cm of tissue thickness 50% of x-ray beam is attenuated
What does higher tissue density mean for attenuation?
more attenuation
(implants most, then bone, then muscle, then fat, and least dense is air)
more dense objects show up more dominantly on the x-ray
What does high tissue atomic number mean for attenuation?
means more attenuation due to more interactions
(more electrons higher chance for photelectric absorption)
Who sets the standards for optimal contrast/brightness settings?
the radiologists
