Exposures II- IR Exposure and Contrast

exposure refers to the:

# of photons striking the IR

conversion factor for nongrid

1

A radiograph that demonstrates a large difference between gray levels would be considered: 1- Short Scale 2- Low Contrast 3- Increased contrast

1 and 3

2 factors that cause exposure to the IR to increase when kVp is increased

1. higher kVp= higher energy electrons have a greater chance of interactions occurring, more photons produced 2. higher energy photons produced have greater penetrability power

why does higher kVp result in lower contrast?

1. photons produced have a wide range of energies, each different energy level produces its own shade of gray = lots of shades of gray 2. more Compton scatter interactions occur

lgm range

1.9 - 2.5

conversion factor for 5:1 grid

2

conversion factor for 6:1 grid

3

If a satisfactory exposure is obtained using 20 mAs, 70 kVp and an 8:1 grid, what mAs is required to maintain exposure to the IR with a 16:1 grid?

30 mAs

conversion factor for 8:1 grid

4

conversion factor for 10:1/12:1 grid

5

conversion factor for 16:1 grid

6

If a satisfactory exposure is obtained using 20 mAs at 40" SID, what mAs would be required to maintain exposure to the IR at 72" SID?

64.8 mAs

If one goes from a technique of 25 mAs and 75 kVp to a 25 mAs and 50 kVp, which of the following will be affected? - exposure to the IR - contrast - distortion - exposure to the IR AND contrast

Exposure to the IR and contrast

T or F. Going from a single-phase generator to a high frequency generator without changing technical factors will decrease exposure to the image receptor.

False

Which of the following will NOT contribute to the underexposure of a radiograph? - mA set too low - kVp set too low - SID set too high - focal spot size is too large

Focal spot size is too large

Which of the following has an inverse relationship with exposure to the IR? - mAs - kVp - film/screen speed - SID

SID

Which of the following may be the cause of an overexposed radiograph? - developer temperature too low - OID too high - SID too low - grid ratio too high

SID too low

T or F. Decreasing grid ratio while keeping all other factors equal, will increase exposure to the IR.

True

T or F. Increasing receptor speed while keeping all other factors equal, will increase radiographic exposure to the image receptor.

True

T or F. Utilizing an increased OID will decrease the exposure to the image receptor.

True

intensity of the beam is less towards the _____ side

anode

Decreasing field size will cause a ______ in exposure to the IR

decrease

If one changes from a 6:1 grid ratio to a 12:1 ratio, how will this affect the exposure to the IR?

decrease

If one goes from using a 10x12 field size to a 14x17 field size, how will this affect the contrast on the radiograph?

decrease

Increasing atomic # will cause a ______ in exposure to the IR

decrease

Increasing tissue thickness will cause a ______ in exposure to the IR

decrease

as OID increases, exposure to the IR will ________

decrease

as SID increases, exposure to the IR will _______

decrease

as filtration increases, exposure to the IR will _____

decrease

as grid ratio increases, exposure to the IR will _____

decrease

decreasing grid ratio will _____ contrast

decrease

increasing atomic part density/ atomic number will _____ the exposure to the IR

decrease

increasing kVp will _____ contrast

decrease

increasing part thickness will _____ exposure to the IR

decrease

increasing tissue thickness will _____ contrast

decrease

increasing window width=

decreased contrast

as field size increases, contrast ______

decreases

as filtration increases, contrast _____

decreases

as part thickness increases, contrast ______

decreases

Which changes would double the exposure to the image receptor?

doubling the mAs; increasing kVp by 15%

lgm

exposure indicator number

when there are large differences between atomic number/tissue density of adjacent structures, the ______ the contrast will be

higher

contrast resolution

how close 2 shades of gray can be and be able to distinguish between them

If one changes from a 5:1 grid ratio to a 6:1 grid ratio, how will this affect the contrast on a radiograph?

increase

Increasing kVp will cause a ______ in exposure to the IR

increase

as IR speed increases, exposure to the IR will ______

increase

as field size increases, exposure to the IR will ______

increase

decreasing field size will ______ contrast

increase

if a grid is added, contrast will _____

increase

if grid ratio is increased, contrast will _____

increase

increasing kVp will _____ exposure to the IR

increase

increasing mAs will _______ exposure to the IR

increase

increasing the generator frequency will ______ exposure to the IR

increase

If you take an original radiograph and want to decrease the contrast along with doubling the exposure, what would be the best choice to accomplish this when repeating your image?

increase the kVp by 15%

as OID increases, contrast _____

increases

Which of the following would decrease exposure to the image receptor with all other factors remaining the same? - increasing mAs - increasing kVp - increasing field size - increasing grid ratio

increasing the grid ratio

Which of the following would increase the contrast on an image? - increasing field size - increasing grid ratio - increasing kVp - increasing part thickness

increasing the grid ratio

additive pathologies

less exposure to the IR

increasing SID and more collimation with make the anode heel effect

less prominent

other terms for low contrast

long scale, lots of shades of gray, wide window width

A radiograph that demonstrates very little difference between gray levels would be considered:

low contrast

higher kVp = ______ contrast

lower

What is our controlling factor of exposure?

mAs

single phase to high frequency

mAs x 0.5

single phase to 3 phase, 6 pulse

mAs x 0.6

3 phase, 6 pulse to single phase

mAs x 1.6

high frequency to single phase

mAs x 2

a higher lgm number means

more exposure (higher mAs); image will be darker

destructive pathologies

more exposure to the IR

underexposed images will appear

more grainy/mottled

the smaller the anode angle, the _______ the anode heel effect

more prominent

Decreasing focal spot size will cause a ______ in exposure to the IR

no change

adjusting the focal spot size will ______ exposure to the IR

not affect

changing IR speed will _____ contrast

not affect

changing SID will ____contrast

not affect

changing from a small focal spot to a large focal spot will ______ contrast

not affect

changing mAs will _____ contrast

not affect

focal spot size will ______ contrast

not affect

the anode heel effect will ______ contrast

not affect

formula for IR speed

old mAs / new mAs = new speed / old speed

grid conversion formula

old mAs / new mAs = old GCF / new GCF

window width

post processing technique with digital systems to adjust contrast

window width manipulations are

post processing techniques

processing that adjusts contrast automatically based on certain anatomy selected

pre-processing (re-scaling)

dynamic range

range of gray levels capable of being represented in an image

what is the purpose of filtration?

remove lower energy photons from the beam

other terms for high contrast

short scale, more black and white, few shades of gray, narrow window width

grid ratio refers to

the amount of lead in the grid

focal spot size affects

the sharpness/detail of an image

purpose of a grid

to absorb scatter photons before they hit the IR

overexposed images will appear

very dark if extremely overexposed; if only a little overexposed a good image will still be produced, just exposes the pt more

Focal spot blooming occurs when

very high technical factors are used