image production 4.2 110420 Flashcards
Receptor exposure may be defined as
Dose area product
The primary controlling factors of receptor exposure
mAs and SID
mAs controls electron flowing thru XR tube and striking anode
Receptor exposure was formerly called
density
The radiograph image is formed by
exit rays striking the image receptor
The number of electrons boiled off the cathode and consequently the number of XRs produced are controlled by
mAs
mAs directly control
The quantity of XRs produced at anode
Visible differences in adjacent structures on a radiographic image describe
contrast resolution
The primary controlling factor of contrast is
KVP and bit depth
KVP controls wavelength and penetrating ability of beam.
In digital imaging window width can be used to manipulate contrast
Which of the following describes the relationship between mAs and receptor exposure
receptor exposure is directly proportional to mAs
The relationship between KVP and receptor exposure may be described as
Direct, although not proportional
It is governed by 15% rule
The active portion of a CR IP is
PSP
The role of KVP in radiographic image production
- As KVP is increased, penetrating ability of the XRs increase
- As KVP is increased, more XRs exit the pt to strike the IR
- As KVP increases, receptor exposure increases
Which of the following governs the relationship between SID and receptor exposure
Inverse square law
If SID is doubled, what may be said about receptor exposure
RE is reduced to 1/4
If SID is reduced by one half, what must be done mAs to maintain a constant receptor exposure
Reduce mAs to 1/4 it
Grey tones (high KVP)
long scale, low contrast
Black and white
short scale, high contrast
lower spatial reso
wide pixel pitch
The variation of XR intensity along the longitudinal axis of the XR beam describes
anode heel effect
XR tube angle
affects receptor exposure
What kind of interactions contribute to differential absorption
Photoelectric interaction
Influenced by atomic number not atomic mass of anatomical structures
What effect does beam restriction have on contrast
increases contrast bc of reduction in the number of Compton interactions that occur
Compton interactions produce scatter which causes contrast to decrease
The adjustment in technical factors reqd when using beam restriction is
increase mAs to compensate for the number of rays removed from the primary beam
What effect does the use of radiographic grids have on contrast
increases contrast by absorbing scatter radiation
As the amount of beam filteration is increased
contrast decreases
Overall wavelength of beam is shorter resulting in lower contrast
spatial resolution is
geometric representation of the part being radiographed
Controlled by SID, OID, focal spot size, ptixel pitch
what SID, OID, focal spot size be for higher spatial reso
long SID, short OID, small focal spot
Optimal spatial reso may be created usng which of the following factors
narrow pixel pitch
Improper use of grids may result in an image artifcact known as
moire pattern
Distortion may be described as
misrepresentation of an anatomic structure on the image
Elongation and foreshortening are examples of
shape distortion
single phase full wave rectification produce
100% ripple and pulsating DC with 120 pulse per sec
3 phase 6 pulse full wave rectification produces
13% ripple DC
3 phase 12 pulse full wave rectification produces
4% ripple DC
The increase in average photon energy with 3 phase 6 pulse equipment compared to single phase
is 35% higher energy than single phase
KVP X MAS X 1.35= heat calculations
The increase in average photon energy with 3 phase 12 pulse equipment compared to single phase
is 41% higher energy than single phase
KVP X MAS X 1.41= heat calculations
single phase equipment average photon energy is
kvp x mas= heat calculations
to get more black and white on image what kind of kvp do you use
lower kvp
= higher contrast = short scale
to get more shades of grey what kind of kvp do you use
high kvp
= low contrast = long scale
different types of interactions with incident e
characteristic or brem
different types of interactions with patient
compton or photoelectric
